Manufacturing Engineering - II Pune University MCQs
Manufacturing Engineering - II Pune University MCQs
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Gear Hobbing”.
1. Hobbing process is also used for which of the following application?
a) Punching
b) Metal bending
c) Rust removal
d) Sprocket cutting
Answer: d
Explanation: Hobbing is a machining process widely used for cutting gears, splines and sprockets. The tool used for cutting is called as a hob.
2. Hobbing is a special type of which of the following?
a) Casting
b) Grinding
c) Drilling
d) Milling
Answer: d
Explanation: Hobbing is a special type of milling in which teeth are cut by a series of cuts made by a tool known as a hob.
3. In the process of gear cutting by hobbing, the angle between the hob’s spindle axis and the workpiece’s spindle axis is fixed.
a) True
b) False
Answer: b
Explanation: The angle between the hob’s spindle axis and the worpiece’s spindle axis varies depending upon the type of product being manufactured.
4. For spur gear manufacturing, angle between the hob’s spindle axis and the workpiece’s spindle axis should be equal to____
a) /2
b) 2*
c)
d) 2
Answer: c
Explanation: As hob has helical threads, it has to be oriented making some angle with the workpiece as per the requirement and then it is fed into the workpiece. For spur gears, that angle should be equal to the helix angle of the hob.
5. For helical gears, the angle between hob’s spindle axis and workpiece’s spindle axis must be _____ as the helix angle of the helical gear.
a) increased by the same amount
b) increased by the half amount
c) decreased by the same amount
d) decreased by the half amount
Answer: a
Explanation: For manufacturing the helical gear, one has to consider helix angle of the gear. While hobbing the helical gear, angle between hob spindle axis and workpiece spindle axis should be increased by an angle equal to helix angle of the gear.
6. Hobbing machines are characterised by _____
a) production rate
b) largest module or PCD it can generate
c) accuracy of the machine
d) size of the machine
Answer: b
Explanation: Hobbing machines are characterised by the largest module or pitch diameter it can generate as they can produce anything from tiny instrument gears to 10ft diameter marine gears.
7. 5in capacity machine can generate gears upto_____ pitch diameter.
a) 5in
b) 10in
c) 15in
d) 20in
Answer: a
Explanation: The number signifies the maximum pitch diameter of a gear that can be produced by that machine. Therefore 5in capacity means the largest gear manufactured by that machine will have pitch diameter equal to 5in.
8. The gear hob is a formed tooth milling cutter with helical teeth.
a) True
b) False
Answer: a
Explanation: The gear hob is a formed tooth milling cutter with helical teeth arranged like the thread on a screw. These teeth are fluted to produce required cutting edges.
9. As the number of threads on the hob increases, it’s accuracy_____
a) increases
b) decreases
c) remains same
d) can’t say
Answer: b
Explanation: More number of threads means more difficulties to manufacture them. Therefore, accuracy varies inversely with a number of hob threads.
10. As the number of threads on the hob increases, production rate______
a) increases
b) decreases
c) with each thread, increases by 25%
d) can’t say
Answer: a
Explanation: Production rate increases with an increase in the number of threads on the hob as more number of threads means less machining time. Directly it cannot be said that production rate will increase by 25% per thread.
11. Ideally how many gear threads should be there or each hob thread?
a) 20
b) 30
c) 45
d) 10 times the number of hob threads
Answer: b
Explanation: For best results, there should be about 30 gear threads for each hob thread. Therefore four-thread hob should not be used to cut fewer than 120 gear teeth.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Bevel Gear Cutting”.
1. Which of the following methods delivers the better rolling performance and higher strength of the manufactured bevel gear?
a) Face milling completing and hard finishing by grinding
b) Face hobbing and hard finishing by lapping
c) Face milling with five-cut and hard finishing by lapping
d) Face milling completing and hard finishing by lapping
Answer: a
Explanation: Bevel gear grinding improves all important properties such as strength, noise characteristics and efficiency. It also requires less investment and follows simple working principle. Lapping typically improves the wear properties of gear tooth, and corrects minute errors in involute profile, helix angle, tooth spacing and concentricity created in the forming, cutting or in the heat treatment of the gears. But the main disadvantage of lapping is that, it is a mating process; two gears that have been matched by lapping should be operated as a set and also replaced as a set, rather than singly.
2. Face milled gear sets are manufactured in_____
a) Single-indexing—one slot at a time
b) Single-indexing¬—two slots at a time
c) Double-indexing—two slots at a time
d) All the slots at a time
Answer: a
Explanation: The milling machine can cut only one tooth/slot at a time. After cutting one tooth, indexing crank is rotated by calculated amount thus taking the workpiece to the proper position for cutting the next tooth.
3. A certain tooth depth taper is applied in all face milled completing bevel gears.
a) True
b) False
Answer: a
Explanation: If a pointed topland occurs on the toe, the teeth of the one member will not fit and roll in slots of the other members if both members are manufactured in a completing process. It is calculated in such a way that it generates a slot width taper that splits the difference in circumference between toe and heel in an equal slot width and tooth thickness taper.
4. What causes an un-proportionally thin and high tooth in the toe region, and a short and thick tooth at the heel?
a) Difference in PCDs of the generating gears
b) Error in indexing while manufacturing
c) Difference in outer and inner circumference of the generating gear
d) Difference in feed rates
Answer: c
Explanation: The difference in outer and inner circumference of the generating gear causes an extreme tooth thickness taper that leads to uneven tooth profile.
5. Face hobbed gear sets are manufactured as continues indexing.
a) True
b) False
Answer: a
Explanation: Face hobbed gears are manufactured using continuous indexing, while the outside blade and the following inside blade of one blade group cut one slot, the following blade group will enter the next slot.
6. Which of the following is a result of the constant relative indexing motion between cutter and workpiece?
a) Un-equal tooth thickness taper
b) Un-equal slot width taper
c) Equal slot width taper and un-equal tooth thickness taper
d) Natural sloth width taper and equal tooth thickness taper
Answer: d
Explanation: The constant relative indexing motion results in an equal split of the inner and outer circumference on the toe and heel as well as an equal split between toe and heel along the entire face width. This leads to a natural slot width taper and equal tooth thickness taper.
7. It is possible to grind face hobbed gears.
a) True
b) False
Answer: b
Explanation: Face milled gears have no slot width taper but a large thickness taper, on the other hand, face hobbed gears have an equal slot width and tooth thickness taper. Therefore, it is impossible to grind face hobbed gears using a cup-shaped grinding wheel.
8. Face hobbed bevel gear sets tend to have their involute point location_____
a) on the flank centre
b) on the addendum circle
c) between addendum and dedendum circle
d) between flank centre and the heel
Answer: d
Explanation: Face hobbed bevel gear sets tend to have their involute point location between the flan centre and the heel, which gives them the reputation of being forgiving with respect to gearbox and gear set deflections.
9. How many indexing methods are there for cutting a gear?
a) 2
b) 4
c) 6
d) 8
Answer: b
Explanation: There are total four indexing methods as listed below—
1) Direct indexing 2) Simple indexing 3) Compound indexing 4) Differential indexing.
10. What will be the indexing to cut 30 teeth on a gear using simple indexing method?
a) Rotate indexing crank by 5 holes in 15 holes circle
b) Rotate indexing crank by 10 holes in 15 holes circle
c) Rotate indexing crank by one complete turn and 7 holes in 21 holes circle
d) Rotate indexing crank by one complete turn and 10 holes in 15 holes circle
Answer: c
Explanation: Crank movement = 40/N
= 40 ⁄ 30
=1 10 ⁄ 30
=1 1 ⁄ 3
Case 1: Multiplying both numerator and denominator by 5
We will get,
Crank movement = 1 5 ⁄ 15
Denominator becomes ‘15’, therefore select 15 hole circle plate.
This means that after each operation rotates indexing crank by one complete turn and 5 holes in 15 holes circle.
Case 2: Multiplying both numerator and denominator by 7
We will get,
Crank movement = 1 7 ⁄ 21
Denominator becomes ‘21’, therefore select 21 hole circle plate.
This means that after each operation rotates indexing crank by one complete turn and 7 holes in 21 holes circle.
Similarly, we can multiply and divide by other numbers too, provided that the index plate with required holes is available.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Broaching”.
1. What is broaching?
a) A machining process used for increasing the size of the existing hole
b) A machining process used for grinding hardened steel
c) A machining process used for making intricate holes accurately
d) A machining process for removal of a layer of material of desired width and depth
Answer: d
Explanation: Broaching is a machining process for removal of a layer of material of desired width and depth usually in one stroke by a slander rod or bar type cutter called as, having a series of cutting edges with a gradually increased protrusion.
2. What is the main advantage of broaching over shaping process?
a) Use of single point cutting tool which are inexpensive and can be grounded to any shape
b) Thin or fragile jobs can be conveniently machined because of lower cutting forces
c) Surfaces with obstruction can also be machined
d) Removal of the whole material in one stroke
Answer: d
Explanation: In shaping, attaining full depth requires a number of strokes to remove the material in thin layers step-by-step by gradually infeeding the single point tool. Whereas, broaching enables remove the whole material in just a single stroke by gradually rising teeth of the cutter called broach. Some are the advantages of shaping process and surfaces with obstruction cannot be machined by broaching.
3. For which of the following operations, broaching can be used?
a) Threading
b) Grinding
c) Spline cutting
d) Increasing the size of the existing hole for a certain length
Answer: c
Explanation: Machining by broaching is preferably used for making straight through holes of various forms and sizes of section, internal and external through straight or helical slots or grooves, external surfaces of different shapes, teeth of external and internal splines and small spur gears.
4. Why push type broaches are made shorter in length?
a) To reduce machining time
b) To increase the efficiency
c) For easy handling of the tool
d) To avoid buckling
Answer: d
Explanation: Both pull and push type broaches are made in the form of slander rod or bar of varying section having along its length one or more rows of cutting teeth with increasing height. Also very high forces are generated during the machining. Therefore, push type broaches are made shorter in length to avoid buckling as they are subjected to compressive load.
5. Why chip breakers are provided on the broach?
a) To reduce machining time.
b) To increase the cutting force by breaking the chips
c) To reduce the friction between tool surface and the workpiece by breaking the chips
d) To break up the wide curling chips
Answer: d
Explanation: Small in-built chip breakers are alternately provided on the roughing teeth of the broaching to break up the wide curling chips and thus preventing them from clogging and increasing force and tool wear. Ductile materials need wider and frequent chip breakers.
6. Why neck section provided in the pull type broaches are made shorter in diameter?
a) To provide better surface finish
b) To remove chips easily
c) To allow failure in case of overloading
d) For holding purpose
Answer: c
Explanation: Neck is one of the essential elements of the broach. Smaller diameter means higher stress concentration. Therefore, in case of overloading neck section will fail first and while keeping the workpiece safe.
7. In broaching, generally the broach remains fixed and the workpiece travels providing cutting velocity.
a) True
b) False
Answer: b
Explanation: In broaching, the workpiece remains stationary throughout the process and the broach travels with the cutting velocity. The broach is also provided with small chip breakers to break up the chips.
8. How many types of broaches are there?
a) 3
b) 5
c) 8
d) 9
Answer: d
Explanation: Various types of broaches have been developed and are used for a wide range of applications. Types of broaches are as follows,
Pull type Push type Ordinary cut type Progressive cut type
Solid type Sectional type Modular type Profile sharpened type
Form relieved type.
9. Which of the following broaches are re-sharpened by grinding at rake faces?
a) Form relieved type
b) Modular type
c) Profile sharpened type
d) Sectional type
Answer: a
Explanation: Form relieved type broaches are sharpened and re-sharpened by grinding at their rake faces. These broaches have more complex cutting edge geometry and varies point-to-point along the cutting edges. Here the product is the replica of the tool form.
10. Which of the following type of broaches are sharpened or re-sharpened by grinding at the flank surfaces?
a) Profile sharpened type
b) Sectional type
c) Segmented type
d) Ordinary cut type
Answer: a
Explanation: Profile sharpened type broaches are sharpened or re-sharpened by grinding at the flank surfaces. These cutters have simple geometry with same rake and clearance angles all over the cutting edge. These broaches are generally designed and used for machining flat surfaces or circular holes.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Shaping”.
1. What is a shaping process?
a) A type of casting process
b) A type of grinding process
c) A metal removal process in which reciprocating workpiece is fed against a stationary tool
d) A process in which metal is removed by a reciprocating tool fed against a stationary workpiece
Answer: d
Explanation: It is a process in which cutting motion provided by linear-forward motion of the reciprocating tool and the intermittent feed motion provided by the slow transverse motion of the workpiece resulting in a flat surface by gradual removal of excess material layer by layer.
2. Which of the following is the advantage of shaping process?
a) Large objects can be machined easily
b) Thin or fragile workpiece can also be machined
c) Lower machining time
d) Higher tool life
Answer: b
Explanation: In shaping process very less cutting forces are generated. Therefore thin or fragile jobs can be conveniently machined. Large objects cannot be machined by shaping, for that purpose planning process is used.
3. What is the purpose of the RAM in shaping machine?
a) To hold the tool
b) To hold the tool head
c) To hold the saddle
d) To hold workpiece
Answer: b
Explanation: Ram supports tool head on its front. It reciprocates on accurately horizontal machined guide ways on top of the column.
4. What is the use of clapper block in the shaper?
a) To hold the tool post
b) To hold the feed handle
c) To house the down feed screw
d) To operate the angular graduation scale
Answer: a
Explanation: Tool post is mounted upon the clapper block to prevent the interface between the tools and workpiece on the return stroke.
5. Clapper block is connected to the clapper box by means of hinge pin.
a) True
b) False
Answer: a
Explanation: The clapper box house the clapper block which is connected to it by means of hinge pin. It prevents the tool cutting edge from dragging and wear. The work surface is also prevented from any damage due to dragging.
6. How many types of shapers are there?
a) 5
b) 8
c) 10
d) 11
Answer: c
Explanation: Shapers are classified as follows:
As per the type of motion.
• Crank type
• Geared type
• Hydraulic type
As per the position and travel of ram.
• Horizontal type
• Vertical type
• Travelling head type
As per the design of the table
• Standard shaper
• Universal shaper
As per the cutting stroke
• Push type
• Draw type.
7. In draw type shaper, the metal is removed when the ram moves towards the machine.
a) True
b) False
Answer: a
Explanation: In this type of the shaper, metal is removed when the ram and thus tool moves towards the column of the machine, i.e. draw the workpiece towards the machine. The ram is generally supported by an overhead arm which ensures rigidity and eliminates deflection of the tool.
8. In travelling head type shaper, ram can move only in vertical direction.
a) True
b) False
Answer: b
Explanation: In travelling head shaper, the ram carrying the tool can move crosswise while it reciprocates to give the required feed. Heavy jobs which are difficult to handle are held static on the basement of the machine while the ram reciprocates and supplies the feeding movement.
9. Which of the following is true about push type shapers?
a) The workpiece moves away from the column machining
b) The ram moves away from the machine column while cutting the metal
c) The ram moves towards the machine column while cutting the metal
d) The ram moves away and the workpiece moves towards the machine column
Answer: b
Explanation: It is the most general type of shaper used in common practice. In this type, the metal is removed when the ram moves away from the column, i.e. it pushes the workpiece. As in shaping process workpiece remains stationary.
10. What will be the cutting time for machining the workpiece of width 1000 mm when the bull wheel is rotating at 150 rpm with the feed of 2 mm per stroke?
a) 90 sec
b) 120 sec
c) 200 sec
d) 500 sec
Answer: c
Explanation: Cutting time is calculated by formula,
CT = W/ (N s *F c ) where, W is width of the work piece
N s is the bull wheel rpm
F c is the feed rate
Therefore,
CT = 1000/
= 3.34 min = 200 sec.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Roll Forming – 1”.
1. Which word best describes the roll forming?
a) Die forming
b) Coining
c) Progressive
d) Profiling
Answer: c
Explanation: Roll forming is a continuous process for forming sheet, strip or coiled metal stock into long shapes of essentially uniform cross-section. The material is fed through pairs of contoured forming rolls, which progressively shape the metal until the desired cross-section is produced.
2. Which of the following are the most desirable materials used in roll forming?
a) Spring steel
b) Chromium-molybdenum steel
c) Non-metals
d) Mild steels and aluminium
Answer: d
Explanation: Both ferrous and non-ferrous metals as well as some non-metallic material can be roll formed. Mild steel and aluminium are the most common materials used in the process. Additionally, polished, painted, coated and plated materials can also be roll formed.
3. The most common cutting method of roll forming is ____________
a) sawing
b) pre-cutting
c) parting
d) post-cutting
Answer: d
Explanation: The stock to be roll formed may be either pre-cut to a pre-determined length before roll forming, or post-cut afterward to a specified dimension. But the latter one is the most common. By incorporating auxiliary equipment such as pre-notching, punching, embossing, etc. the post-cut method can be a complete net-shape process, fully automated.
4. Pre-cut roll forming production speed are ______________
a) 600 to 800 feet per minute
b) up to 1000 feet per minute
c) 50 to 250 feet per minute
d) 100 to 300 feet per minute
Answer: c
Explanation: In the pre-cut method, material passes through the rolls at fixed speeds of 50 to 250 feet per minute or 15 to 76 meters per minute. Pre-cut roll forming is commonly used for low production when nothing is required that cannot be easily done using post-cut lines, or when multiple profile widths require expensive and or time consuming tool changeover.
5. Post-cut roll forming production speeds are ______________
a) 100 to 180 feet per minute
b) 650 to 780 feet per minute
c) 800 to 900 feet per minute
d) up to 100 feet per minute
Answer: a
Explanation: The post-cut method typically involves a stock uncoiler, a roll forming machine, and a runout table. Production speeds average 100 to 180 feet, or 30 to 55 meters per minute, but can be as high as 600 feet or 185 meters per minute.
6. Camber refers to deviation from a straight line the____
a) side edge before roll forming
b) vertical plane
c) horizontal plane
d) side edge after roll forming
Answer: a
Explanation: Depending on the length, roll forming length tolerance of plus or minus 0.020 to 0.093 of an inch, or 0.51 to 0.236 of a millimetre are possible. To determine the straightness few terms are used and camber being one of them. Camber means the deviation a side edge from a straight line measured prior to roll forming.
7. When does springback occur?
a) When the material does not stress beyond its elastic limit
b) When the material is stressed beyond its elastic limit
c) When the material is too hard
d) When the material is too soft
Answer: a
Explanation: Elastic limit is the point beyond which material deforms permanently under stress. Springback is the tendency to regain the initial shape. Therefore, it occurs when the material does not stress beyond its elastic limit during forming. Spring is often compensated by overforming the material and then allowing it to ‘spring back’ to the required profile.
8. The flower design is____
a) the total number of formed bends
b) a station-by-station overlay of progressive part contours
c) the part’s finished profile
d) the finished profile divided into component bends and straight sections
Answer: b
Explanation: The design of forming rollers is dependent on several factors such as number of forming passes, material width, roll material, flower design, etc. Flower design is a station-by station overlay of the progressive part contours starting with the flat strip width before forming and ending with the final desired section profile.
9. Which of the following is the most common material used to produce forming rolls?
a) Aluminium
b) Carbide
c) Chrome steels
d) Oil hardened tool steels
Answer: d
Explanation: Several types of materials are used in the manufacture of the forming rolls and oil hardened tool steel being the most common. For extended tool life, hardened high-carbon, high-chromium too steels are used. On extremely tough forming applications involving high temperatures and or abrasive materials, aluminium/bronze or carbide rolls are required.
10. Why spacers are used in roll forming machines?
a) To prevent the springback of the material
b) To fix the rolls in exact position
c) To accommodate specific material thickness by adjusting the height
d) To support the shaft
Answer: b
Explanation: Spacers are used to fix the rolls in the exact position on the spindles. Vertical adjustment of the top shaft fine tunes the machine to accommodate specific rolls and material thickness.
This set of Manufacturing Processes Interview Questions and Answers focuses on “Roll Forming – 2”.
1. EP 2 grease, high-temperature grease and chain and open-gear grease are used in roll forming equipment.
a) True
b) False
Answer: a
Explanation: EP 2 grease is used lubricating gears. This gear can handle heavy, suddenly applied loads in bearing application. High-temperature grease is used in weld boxes and other equipment that is subjected to a temperature above 200°F. Chain and open-gear grease are used on chain couplings, chain-driven components and open gear drives.
2. Which of the following oils is used in roll forming equipment?
a) SAE 140
b) SAE 30
c) Linseed oil
d) SAE 5W-30
Answer: a
Explanation: ISO grade 460 Gear oil is used in sealed gearboxes. Gear oil has extreme pressure additives that strengthen the non-detergent oils to withstand heavy loads found in gears and gear drive systems.
3. In how many types roll forming lubricants are categorised?
a) 3
b) 5
c) 6
d) 4
Answer: b
Explanation: The different types of roll forming lubricants are listed below:
1. Evaporator compounds or vanishing oils
2. Chemical solutions
3. Micro-emulsions
4. Macro-emulsions
5. Petroleum based lubricants.
4. Chemical solutions ideal for coated steel.
a) True
b) False
Answer: a
Explanation: Chemical solutions are one of the fastest growing roll forming lubricant family. They are economical, environmentally safe, easy to handle, and are ideal for use on coated, galvanised, cold roll steel, aluminium, and in some instances, stainless steel.
5. Which of the following is used for lubrication in heavy-duty roll forming?
a) Extreme pressure-type solutions
b) Soap-type solutions
c) Non-ionic type solutions
d) Micro-emulsions
Answer: b
Explanation: The soap-type solutions are used for heavy-duty roll forming. Non-ionic type solutions are excellent for roll forming aluminium and coated components and extreme pressure-type are used for high strength alloys.
6. For which of the following materials evaporative lubricants are used?
a) Hot rolled steel
b) Stainless steel
c) Ferrous and non-ferrous materials
d) Aluminium
Answer: c
Explanation: Evaporative lubricants are used for roll forming of painted, coated, and vinyl surfaces as well as ferrous and non-ferrous materials. They are applied using the proper type of airless spray system.
7. Which of the following is ideal for lubrication in roll forming of hot rolled and cold rolled steel?
a) Micro-emulsion
b) Macro-emulsion
c) SAE 120
d) SAE 20W 40
Answer: a
Explanation: micro-emulsions provide some film strength from the combination of emulsifiers, water-soluble corrosion inhibitors, wetting agents, organic and inorganic salts, and sometimes extreme pressure agents.
8. Macro-emulsions are also called as soluble oils.
a) True
b) False
Answer: a
Explanation: Macro-emulsions contain an oil-based lubricant, such as a mineral or compounded oil in the form of suspended droplets, which have been dispersed with emulsifiers due to which they become milky white appearance. Therefore, they are sometimes misleadingly called soluble oils.
9. Why additives are mixed with lubricating oil?
a) To reduce the friction
b) To increase the heat transfer
c) To change the colour
d) To improve the lubricant properties
Answer: d
Explanation: Additives are mixed to adjust the lubricants and make the suitable for a specific application. Additives improve lubricant’s properties, protect metal surfaces as well as perform many other functions.
Examples of additives: Rust and corrosion additives, EP additives, etc.
10. Pick the odd one out.
a) Sulphur compounds
b) Nitrates
c) Phosphorous compounds
d) Chlorine compounds
Answer: b
Explanation: Nitrates are usually used as rust or corrosion inhibitors; whereas compounds of sulphur, chlorine and phosphor are extreme pressure additives.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Roll Forming – 3”.
1. During roll forming, a flat strip is passed number of times through the rollers.
a) True
b) False
Answer: a
Explanation: In roll forming, a flat strip is gradually formed to the finished shape. The forming is almost exclusively accomplished by rotating contoured rolls while the material passes through the mill.
2. Which of following is necessary in order to have a good set of rolls?
a) Short horizontal distances
b) Small lead-in flanges
c) A smooth flow of material
d) Less number of forming passes
Answer: c
Explanation: The probability of having a good set of rolls is to follow few rules:
Envision a smooth flow of material,
Do not be skimpy with the number of forming passes,
Avoid too short horizontal distances and too small lead-in flanges.
3. Which of the following is true in case of “too quick” forming ?
a) It makes the tooling and the process uneconomical
b) It makes process easier
c) It distorts the product
d) Eliminate the need of a skilled operator
Answer: c
Explanation: “Too quick” forming will distort the product because of the unacceptable level of stresses generated in the metal. On the other hand, too many passes will make the tooling and the process uneconomical.
4. What is “leg length” or “leg height”?
a) The maximum vertical dimension of the profile
b) Total length of the product
c) Excess length of the product
d) Maximum width of the section
Answer: a
Explanation: The depth of the section, also called as “leg length” or “leg height”, is the maximum vertical dimension of the profile as it exits from the last pass. Sometimes it called as “depth of corrugation”.
5. In case of “U” channel/ section, the length of travel of the edge of the strip ‘s’, travelling in a helical pattern having initial length ‘l’ is given by_____
a) l 2 = s 2 + c 2
b) c 2 = l 2 + s 2
c) s 2 = l 2 + c 2
d) s = l 2 + c 2
Answer: c
Explanation: As we know, edge of the strip to be bend travels in a helical path, the length of the strip after bending is given by formula:
s 2 = l 2 + c 2 , where, s = final length &
l = initial length.
6. What will be the elongation if a 1in high section is formed in four passes in a mill having a horizontal distance of 14in?
a) 0.04%
b) 0.16%
c) 0.63%
d) 0.50%
Answer: a
Explanation: Here, h = 1in; number of passes = 4 and each of length = 14in
Therefore, l = 4 * 14 = 56.
manufacturing-technology-problems-q6
Therefore,
Elongation, e = / 56
= 0.0004 = 0.04%.
7. During roll forming, the strain of the outside edge fiber of the strip must remain below the uniform engineering strain .
a) True
b) False
Answer: a
Explanation: If the strain exceeds the elastic limit, then the edge of the finished product will become permanently strained. Due to which the finished product will be wavy or the product will have a bow, camber or twist.
8. What is camber in roll forming?
a) Deviation of the strip edge from a straight line in horizontal plane
b) Deviation of the strip edge from a straight line in vertical plane
c) Difference in theoretical and actual elongation of the strip
d) Waviness of the strip
Answer: a
Explanation: Camber is the deviation of the strip edge from a straight line in the horizontal plane. The inside concave edge of the strip is shorter than the outside convex edge. The shorter edge will be under tension and the longer edge will be compressed.
9. When an asymmetrical section is roll formed, the finished product will have _____
a) Camber
b) Cross-bow
c) A twist
d) Waviness
Answer: c
Explanation: When an asymmetrical section is a roll formed, the finished product will have a twist after leaving the last pass, even if the starting material is flat.
10. When forming “Z” sections, the product is twisted in the opposite direction to compensate the machine generated twist.
a) True
b) False
Answer: a
Explanation: A common method used to compensate for the anticipated twist is to twist the product in the opposite direction in the mill, from pass to pass. This principle is used when forming “Z” sections. In other cases, the counter-twisting is accomplished just in the last one or two passes.
This set of Manufacturing Processes Questions and Answers for Freshers focuses on “Roll Forming – 4”.
1. The minimum bend radius for bending material in roll forming is one stock thickness.
a) True
b) False
Answer: a
Explanation: The minimum radius used is one stock thickness; however 2 times stock thickness is preferable. Bending radius smaller than one stock thickness is possible to use but the life of rolls reduces significantly.
2. The parts shorter than_____ the centreline spacing of rolls of the machine employed will not feed or form satisfactorily.
a) 2 times
b) 3 times
c) 4 times
d) 5 times
Answer: b
Explanation: It is preferred to produce the stock in longer lengths and cut the desired length after forming. This operation needs to carry out in a continuous automatic manner. A thumb rule on this is that, the parts shorter than 3 times the centreline spacing of rolls of the machine employed will not feed or form satisfactorily.
3. Depth of roll formed section should be kept as small as possible.
a) True
b) False
Answer: b
Explanation: Smaller depth helps to simplify tooling, reduce tooling wear and preserve the stock finish. The maximum form depth that has been established for average-size forming machines is 100 mm.
4. The waviness can be seen in the formed product if unformed areas are less than _____ wide.
a) 100 mm
b) 120 mm
c) 125 mm
d) 150 mm
Answer: c
Explanation: Wide parts show some kind of waviness unless unformed areas are less than 125 mm wide. Waviness or other type of irregularity in wide areas can be avoided with the help of longitudinal stiffening ribs.
5. Waviness at the edges can be avoided by_____
a) longitudinal stiffening ribs
b) incorporating a flange
c) using roller support at the edges
d) waviness can never be avoided
Answer: b
Explanation: Waviness or unevenness at the edges can be avoided by incorporating a flange, hem, or rib near or at the edge. Longitudinal stiffening ribs are used to minimize irregularity in the areas of the product.
6. In roll forming, exact vertical side walls are avoided.
a) True
b) False
Answer: a
Explanation: In roll forming, exact vertical side walls are avoided to reduce excessive roll wear and scoring. A draft angle equal to 0.5° or more is preferred.
7. Why blind corners and radii should be avoided while roll forming?
a) It needs an additional setup
b) It is time consuming
c) Skilled labour is a need for that
d) Less accuracy
Answer: d
Explanation: Blind corners and radii are feasible but should be avoided. Because they are less accurate than the corners formed with rollers in contact with both sides of the stock.
8. Forming of any metal, however, must be achieved with stresses above the yield stress.
a) True
b) False
Answer: a
Explanation: If the material is stressed below yield point, it would spring back to its original shape. Therefore, material should be stressed beyond the yield point. But bear in mind that stress should not exceed the maximum tensile stress; otherwise the product will crack or tear during forming.
9. It is difficult to form materials with high yield and ultimate tensile strength. Why?
a) High ductility
b) High fatigue strength
c) Lower creep resistance
d) Lower elongation
Answer: d
Explanation: The larger the difference between yield and ultimate tensile strength, larger is the elongation, thus, better the chance to form the metal. It is very difficult to form metals with extremely high yield and ultimate strength and having a near zero elongation. These materials will crack at the sharp bends because the elongation in the outside fibres would be larger than maximum elongation.
10. What will be the theoretical elongation of outside fibre in ratio to the neutral axis, if inside bend radius is equal to the material thickness and the bending factor is equal to 0.33?
a) 14.5%
b) 25.3%
c) 40%
d) 50.3%
Answer: d
Explanation:
Given: 1) r = t
2) k = 0.33
Solution: Let, bend angle = α
Length of the outside fibre= l o =*α
Length of the neutral axis = l n = * α
Therefore, theoretical elongation = ( l o – l n )/ l n
= [*α – * α]/ * α
As, r=t and k=0.33,
Elongation= 0.503 = 50.3%.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electromagnetic Forming”.
1. Which of the following is not used in electromagnetic forming process?
a) A capacitor bank
b) A forming coil
c) A foeld shaper
d) Stiffening ribs
Answer: d
Explanation: The EMF process uses a capacitor bank, a forming coil, a field shaper, and an electrically conductive workpiece to create intense magnetic fields that are used to do the useful work.
2. Which of the following is true about EMF process?
a) Intense electric field is produced using capacitors and coils
b) Heavy current is made to flow through the workpiece
c) Intense magnetic field is produced for few microseconds
d) Principle of electromagnetic induction is used to pre-heat the workpiece
Answer: c
Explanation: In EMF process, very intense magnetic field is produced by the discharge of capacitor bank into a forming coil, which lasts for only a few microseconds.
3. In EMF process, eddy currents are induced in a conductive workpiece.
a) True
b) False
Answer: a
Explanation: In EMF process, eddy currents are induced in the workpiece which is placed close to the coil. When these eddy currents interact with the magnetic field, cause mutual repulsion between the workpiece and the forming coil due to which workpiece is stressed beyond its yield strength, resulting in permanent deformation.
4. In EMF process, forming pulse rate is kept as high as possible
a) True
b) False
Answer: b
Explanation: As the workpiece surface moves inward under the influence of the pressure generated by the repulsive force, it absorbs energy from the magnetic field. To apply most of this available energy to forming, and to reduce energy loss due to permeation of the workpiece material, the forming pulse is kept short. In most forming aplications, pulses have a duration between 10 to 100 seconds.
5. For EMF process, resistivity of the workpiece material should be _____________
a) greater than 10 micro-ohm-cm
b) less than 8 micro-ohm-cm
c) less than 15 micro-ohm-cm
d) in the range 10-20 micro-ohm-cm
Answer: c
Explanation: The efficiency of the magnetic pulse forming depends upon the resistivity of the metal being formed. For good results, the resistivity of the material should be less than 15 micro-ohm-cm.
6. Which of the following is not true about EMF?
a) Leaves tool marks
b) Does not require lubrication
c) Does not require any cleanup
d) It is primarily applied in the forming of good conducting materials
Answer: a
Explanation: In EMF pressure is applied by a magnetic field, unlike other mechanical processes in which a tool contacts a workpiece. Therefore, it requires no lubrication, leaves no tool marks and requires no cleanup after forming.
7. Springback effect of the workpiece material is eliminated in EMF process.
a) True
b) False
Answer: a
Explanation: In EMF, the material is loaded into its plastic region, resulting in permanent deformation, so that the springback associated with mechanical processes is vertually eliminated because there is no mechanical contact.
8. The maximum pressure applied by the compression coil is approximately _______________
a) 300 MPa
b) 340 MPa
c) 375 MPa
d) 400 MPa
Answer: b
Explanation: The maximum pressure that can be applied by standard compression coils is approximately 340 MPa, thus process is restricted to a relatively thin-wall tube or sheet products.
9. Electromagnetic forming is rarely used to form tubular shapes.
a) True
b) False
Answer: b
Explanation: Electromagnetic forming is chiefly used to expand, compress, or form tubular shapes. It is occasionally used to form flat sheet, and it is often used to combine several forming and assembly operations into a single step.
10. The die used in electromagnetic process should be made of material with _________________
a) high electrical conductivity
b) low electical conductivity
c) low ductility
d) high creep resistance
Answer: b
Explanation: The die used in the electromagnetic process should be made of low electrical conductivity to minimize the magnetic cushion effect. Dies are generally made of steel or epoxy resin.
11. The EMF process allows increased ductility for______________ alloys.
a) Chromium – molybdenum
b) aluminium
c) nickel
d) chromium – mangnese
Answer: b
Explanation: The EMF process allows increased ductility for certain aluminium alloys because of the lack of mechanical stress and friction normally encountered with mechanical processes.
12. Tooling for EMF process is relatively inexpensive.
a) True
b) False
Answer: a
Explanation: The machine and the work coils required in EMF process can be viewed as general-purpose tooling. Therefore it can be said that the tooling for this process is inexpensive.
13. EMF is primarily used for which of the following material?
a) Silver
b) High carbon steel
c) Chromium alloys
d) Martensitic steel
Answer: a
Explanation: This process is primarily applied in the forming of good conducting materials such as copper, aluminium, silver and low carbon steel. It can also be used to form a poor conductor like stainless steel.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Grinding”.
1. In electro-chemical grinding, grinding wheel is used as a cathode.
a) True
b) False
Answer: a
Explanation: ECG is similar to electro-chemical machining, only difference is the abrasive grinding wheel is used as a cathode instead of a tool shaped like the contour to be machined.
2. ECG is suitable for which of the following materials?
a) Tungsten carbide
b) Polymers
c) Iron
d) Nickel
Answer: a
Explanation: ECG is used primarily to machine difficult to cut alloys such as stainless steel, hastelloy, inconel, monel, waspally and tungsten carbide, heat treated workpieces, fragile or therm-sensitive parts, or parts for which stress-free and burr free results are required.
3. In ECG, grinding action removes ____________
a) workpiece material from the surface
b) corroded surface layer making workpiece ready for electro-chemical process
c) oxide film formed on the surface
d) particles removed from surface after chemical action
Answer: c
Explanation: ECG removes metal by combination of electro-chemical and grinding actions. The grinding action removes the buildup of oxide film on the surface of the workpiece.
4. As compared to electrochemical machining , ECG consumes less power.
a) True
b) False
Answer: a
Explanation: Power required for ECG is less than for ECM since the machining area is smaller and the abrasive grinding wheel removes the oxide film, thus preventing the excess use of chemical/electrolyte.
5. Nozzles are used to _____________
a) spray coolant on the wheel
b) ensure proper wetting of the wheel
c) spray chemical directly on the work piece
d) nozzles are not used in ECG
Answer: b
Explanation: Nozzles are used to ensure proper wetting action of the wheel. Nozzle creates a partial vacuum and causes the electrolyte to be sucked up, filling the cavities around the grit. The rotation of the wheel carries the electrolyte into the area of contact.
6. In ECG, rate of formation of oxide film is faster than that in ECM.
a) True
b) False
Answer: a
Explanation: The electrolyte used in ECG is designed to enable faster formation of oxide films on the workpiece, whereas in ECM, the oxide film must dissolve at once in the electrolyte.
7. Electrolyte in ECG should provide _____________
a) lower chemical activity
b) allowance to stray currents
c) high stock removal efficiency
d) higher corrosion tendency
Answer: c
Explanation: Desirable electrolyte should provide: high conductivity, high stock removal efficiency, passivation to limit stray currents, good surface finishes and corrosion inhibition.
8. Which of the following is true for ECG?
a) Higher the grinding wheel rpm, higher is the MRR
b) Higher the current density, faster the removal rate
c) Stronger the electrolyte, poor surface finish
d) Higher the hardness of the workpiece, lower the current density required
Answer: b
Explanation: The removal rate for ECG is governed by the current density, just as in ECM: as with ECM, the higher the current density, the faster the removal rate and better the resulting surface finish.
9. Feed rates in ECG vary with a grinding method.
a) True
b) False
Answer: a
Explanation: In ECG. Feed rates vary with different parameters, depending on the grinding method: if the feed rate is running too slowly for the application, a large overcut will be produced that will result in poor surface finishes and tolerances and if the feed rate is too fast, the abrasive particles will be prematurely forced in too the workpiece, resulting in excessive wheel wear.
10. Which of the following is true about ECG?
a) Lower MRRs when grinding hard, heat sensitive materials
b) Machining of soft metals like aluminium can be easily done
c) Difficult to machine materials with high hardness like tungsten carbide
d) Burr-free sharpening of needles
Answer: d
Explanation: Applications of ECG are as follows;
Single largest use for ECG is in the manufacturing and remanufacturing of turbine blades and vanes for aircraft turbine engines
Grinding of tungsten carbide tool inserts
Re-profiling worn locomotive traction motor gears
Burr-free sharpening of hypodermic needles
Grinding of surgical needles, other thin wall tubes, and fragile parts
Machining of fragile or very hard and tough material – honey comb, thin walled tubes and skins
High MRR’s when grinding hard, tough, stringy, work-hardenable or heat sensitive materials.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electro-Chemical Machining – 1”.
1. Electro-chemical machining is opposite of electrochemical coating.
a) True
b) False
Answer: a
Explanation: In electrochemical or galvanic coating, some another material is coated on the workpiece metal; whereas in Electro-chemical machining, material is removed from the workpiece.
2. ECM can also be called as un-controlled anodic dissolution.
a) True
b) False
Answer: b
Explanation: ECM can be thought of a controlled anodic dissolution at atomic level of the workpiece that is electrically conductive by a shaped tool due to flow of high current at relatively low potential difference through an electrolyte which is quite often water based neutral salt solution.
3. For ECM of steel which is used as the electrolyte?
a) Kerosene
b) NaCl
c) Deionised water
d) HNO 3
Answer: b
Explanation: During ECM, there will be reactions occurring at the electrodes i.e. at the anode or workpiece and at the cathode or the tool along with within the electrolyte. For electrochemical machining of steel, generally a neutral salt solution of sodium chloride is taken as the electrolyte.
4. MRR is ECM depends on _____________
a) hardness of work material
b) atomic weight of work material
c) thermal conductivity of work material
d) ductility of work material
Answer: b
Explanation: In ECM, material removal takes place due to an atomic dissolution of work material. Electrochemical dissolution is governed by Faraday’s laws. Also, for ECM, MRR= IA/, where I= current, ρ= density of the material, A= atomic weight, v= valency, F= faraday’s constant.
5. For which of the following ECM cannot be undertaken?
a) Steel
b) Nickel based superalloy
c) Aluminium oxide
d) Titanium alloy
Answer: c
Explanation: ECM can machine any electrically conductive work material irrespective of their hardness, strength or even thermal properties. In ECM, material is removed from the workpiece by oxidizing it. Aluminium oxide cannot be oxidized further; therefore it cannot be machined by ECM.
6. Commercial ECM is carried out at a combination of ___________
a) low voltage high current
b) low current low voltage
c) high current high voltage
d) high voltage only
Answer: a
Explanation: As we know, in ECM, MRR= IA/, where I= current. Therefore, the amount of electrochemical dissolution or deposition is proportional to the amount of charge passed through the electrochemical cell, i.e.
m∝Q, where m = mass of material dissolved or deposited
Q = amount of charge passed.
7. In ECM of pure iron a material removal rate of 600 mm3/min is required. What will be the current requirement?
a) 157A
b) 183.6A
c) 247.8A
d) 268.8A
Answer: d
Explanation: MRR= IA/
MRR = 600 mm 3 /min = 600/60 mm 3 /s = 10 mm 3 /s = 10×10 -3 cc/s
A= 56,
v= 2,
F= 96500 coulomb, and
ρ = 7.8 gm/cc
Therefore, I= (96500*10*10 -3 *7.8*2)/56
I= 268.8A.
8. In ECM operation of pure iron an equilibrium gap of 2 mm is to be kept. What will be the supply voltage , if the total overvoltage is 2.5 Volts. The resistivity of the electrolyte is 50 Ω-mm and the set feed rate is 0.25 mm/min.
a) 5v
b) 7.8v
c) 11.3v
d) 13.2v
Answer: d
Explanation: h= c/f
Where, c= *A/
Therefore, c= *56/(96500*7.8*10 -3 *50*2)
c= /1344.1
Now, h= c/f
2= [/1344.1]/[0.25/60] Therefore, v= 13.2 volts.
9. In ECM, workpiece acts as a cathode.
a) True
b) False
Answer: a
Explanation: In ECM, material is depleted from anode workpiece and transported to a cathode tool in an electrolyte bath. Electrolyte flows rapidly between two poles to carry off depleted material, so it does not plate onto tool.
10. Electrolyte used in ECM should have _____________
a) high specific heat
b) lower resistance to film formation on the workpiece
c) higher viscosity
d) corrosive nature
Answer: a
Explanation: Desirable properties of the electrolytes are as follows:
• High electrical conductivity – for easy ionization
• Low viscosity – for easy flow
• High specific heat – to carry more heat
• Chemical stability – to be chemically neutral or
does not disintegrate during the reaction
• Resistance to formation of passivating film on
the workpiece surface
• Non corrosiveness and non-toxicity
• Inexpensiveness and easy availability.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electro-Chemical Machining – 2”.
1. Which of the following holds true about electro-chemical machining?
a) Material is removed from the cathode and deposited on the anode
b) Material is removed from the anode and carried away by the electrolyte
c) Major drawback is that the finished product has residual stresses
d) It can also be used for all non-metals
Answer: a
Explanation: In ECM, material is depleted from anode workpiece and transported to a cathode tool in an electrolyte bath, but instead of depositing it on cathode, it is carried away by the electrolyte which flows rapidly between two poles.
2. ECM process is based on which of the following laws?
a) Coulomb’s law
b) Faraday’s law
c) Law of definite proportions
d) Law of chemical combination
Answer: b
Explanation: that if two electrodes are placed in a bath containing a conducting liquid and a DC potential is applied across them, then metal can be depleted from the anode and plated on the cathode – process universally used in electroplating by making the workpiece the cathode. In ECM, the material is removed and hence the workpiece is made the anode.
3. Which of the following conditions are desirable for ECM?
a) High value DC and low value electric potential
b) Low value DC and high value electric potential
c) High value DC and high value electric potential
d) Low value DC and low value electric potential
Answer: a
Explanation: In ECM, high value DC and a low value of electric potential across the IEG is desirable.
4. In ECM, material removal rate does not depend on chemical properties of the anode material.
a) True
b) False
Answer: b
Explanation: Only electrically conductive workpieces can be machined by ECM process. In this process workpiece material work as an anode, therefore the chemical properties of the anode material largely govern the MRR.
5. Which of the following materials can be used for making work holding devices?
a) Steel
b) Rubber
c) Graphite fibres
d) Wood
Answer: c
Explanation: Work holding devices are made of electrically non-conductive materials having good thermal stability, and low moisture absorption properties. For example, graphite fibres-reinforced plastics, plastics, perspex, etc.
6. In ECM, shape of the cathode does not affect the shape of the machined product.
a) True
b) False
Answer: b
Explanation: In ECM, workpiece is used as an anode and cathode is made up of some conducting materials like aluminium, copper, brass, titanium, etc. In this process, product gets the shape which is inverse as that of the tool .
7. Which of the following is true about ECM process?
a) Unable to machine high strength materials
b) Excessive tool wear
c) It gives burr free surface
d) Surface hardness of the workpiece gets reduced
Answer: c
Explanation: Following are the advantages of ECM process;
• Can be used to machine complex cavities in high strength material
• Applications in aerospace industry, jet engines parts and nozzles
• ECM process gives a burr free surface
• No thermal damage
• Lack of tool forces prevents distortion of the part
• No tool wear.
8. Tool used in ECM should have higher rigidity.
a) True
b) False
Answer: a
Explanation: In ECM, rigidity of the tool construction and material is important because the high pressure can cause deflection of the tool. Therefore, materials like copper-tungsten, titanium, cupro-nickel, stainless steel, etc. are used for making tools.
9. The tool in ECM should have which of the following properties?
a) High machinability
b) Lower corrosion rate
c) High softness
d) High conductive resistance
Answer: a
Explanation: Tool material should have the following properties:
• High electrical and thermal conductivity
• Good stiffness
• High machinability- particularly important if complex shaped tools are required
• High corrosion resistance- to protect itself from corrosive electrolytes
• High rigidity.
10. For ECM, tool dimensions are different from the actual mirror dimensions of the part to be machined.
a) True
b) False
Answer: a
Explanation: In ECN, tool dimensions must be slightly different from the nominal mirror dimensions of the completed part to allow for ECM overcut. Designer must also determine the nature and the extent of the required deviation or gap allowances from the mirror image configuration while providing a uniform and sufficiently high flow rate of electrolyte in the gap to allow a practical MRR.
This set of Manufacturing Processes Interview Questions and Answers for freshers focuses on “Electro-Chemical Machining – 3”.
1. In ECM, one needs to understand fluid flow while designing the tool for machining complex shapes.
a) True
b) False
Answer: a
Explanation: Because of the interaction of working-tip shape and dimensions, location of insulation, current density and feed rate, the design of tools for machining complex shapes requires understanding of fluid flow, electrical and electrochemical principles as well as experience and ingenuity.
2. Which of the following does not hold true about ECM?
a) ECM cell must avoid flutter and arcing
b) Part and the cathode must have adequate current-carrying capacity
c) Tool must have shape exactly same as that of the mirror image of the part
d) It gives burr free surface
Answer: c
Explanation: Tool dimensions must be slightly different from the nominal mirror dimensions of the completed part to allow for ECM overcut. ECM cell must have strength and rigidity to avoid flutter and arcing.
3. For which of the following ECM cannot be used?
a) Tapering a predrilled hole in iron block
b) To make stepped hole is a nickel alloy
c) To generate ribs on metal surface
d) To machine Al 2 O 3
Answer: d
Explanation: Open-flow cathode is used to generate the outside diameter wall and leave an embossment. Stepped tool is used for sinking a stepped through-hole. Cone shaped tool is to generate taper in a predrilled hole. Al 2 O 3 cannot be machined by ECM as it is ceramic.
4. Electrolyte should carry away the heat generated and products of the reaction.
a) True
b) False
Answer: a
Explanation: Electrolyte used in ECM should-
• Complete the electrical circuit between the tool and the workpiece
• Allow the desirable machining reactions to take place
• Carry away the heat generated during the operation
• Carry away products of reaction from the zone of machining.
5. Which of the following is not a desirable electrolyte property?
a) Low viscosity
b) High specific heat
c) Lower resistance to film formation on the workpiece
d) Non-corrosiveness
Answer: c
Explanation: Desirable electrolyte properties are as follows-
• High electrical conductivity – ease in ionisation
• Low viscosity – for easy flow
• High specific heat – to carry more heat
• Chemical stability – to be chemically neutral or does not disintegrate during the reaction
• High resistance to formation of passivating film on the workpiece surface
• Non corrosiveness and non-toxicity
• Inexpensiveness and easy availability.
6. Electrolyte flow plays an important role in ECM.
a) True
b) False
Answer: a
Explanation: Need for sufficient electrolyte flow between the tool and the workpiece-
• To carry away the heat and the products of machining
• To assist the machining process at the required feed rate, producing a satisfactory surface finish, cavitation, stagnation and vortex formation should be avoided since these lead to bad surface finish
• There should be no sharp corners in the flow path. All corners in the flow path should have a radius.
7. Which of the following is a sludging type electrolyte?
a) NaOH solution
b) KOH solution
c) NaCl solution
d) CuSO 4 solution
Answer: c
Explanation: There are two types of electrolytes-
Sludging type: These are solutions of salts which forms precipitate after reaction with metals. For example: solutions of typical salts like NaCl.
Non-sludging type: These are solutions of salts which do not form heavy precipitate or form soluble compounds after reacting with metals. For example: strong alkali solutions.
CuSO 4 does not form any solution.
8. Tool with an electrolyte supply slot leaves small ridge on the work.
a) True
b) False
Answer: a
Explanation: Tool with an electrolyte supply slot is simple to manufacture, but such a slot leaves small ridges on the work. However, the ridges can be made very small by making the slot sufficiently narrow. The flow from a slot takes place in a direction perpendicular to the slot and the flow at the end is poor – therefore the slot is terminated near the corners of the workpiece surface.
9. The insulation in ECM should have_____
a) adhesion to the tool
b) roughness
c) high water absorption tendency
d) chemically active
Answer: a
Explanation: Desirable qualities of insulation are as follows-
• Adhesion to the tool: preformed insulation can be held to the tool by shrink fitting, adhesives or fasteners
• Sealing without pores or leaks that could cause stray machining by current leakage
• Adequate thickness
• Smoothness to avoid disturbing the flow of electrolyte
• Resistance to heat for continuous service at 200°C without breakdown
• Durability to resist wear in guides and fixtures
• Chemical resistance to the electrolyte
• High electrical resistivity
• Uniform application to minimize disturbance of the flow of electrolyte and to prevent interference
• Low water absorption.
10. Spraying or dipping method is used for applying insulation.
a) True
b) False
Answer: a
Explanation: Generally the simplest method of applying insulation is by spraying or dipping. Teflon, urethane, phenolic, epoxy, powder coating and other materials are commonly used for insulation. Sprayed or dipped coatings of epoxy resins are among the most effective insulating materials. For optimum effectiveness, these coatings should be used with a protective lip on the tool to protect the edge of the insulation from the flow force of the electrolyte.
11. Which of the following does not hold true about ECM?
a) Lower current density leads to poor surface finish
b) Small gap between tool and the workpiece can cause short circuit
c) Gap between the tool and the workpiece doesn’t affect the process parameters
d) MRR is dependent on feed rate and electrolyte composition
Answer: c
Explanation: Current density is not only controlled by the amount of current that the power supply is delivering, but also by the size of the gap. A small gap results in the highest current density. However, when it’s very small, there is a danger of sludge particles bridging the gap and causing a short circuit. When the gap is too large, current density is reduced, resulting in a poor surface finish and decreased MRR.
12. Pick the incorrect one from the following options.
a) Voltage across the cutting gap influences the current and the MRR
b) Higher voltage decreases the equilibrium machining gap
c) Increased current leads to electrolyte heating
d) ECM can be used for facing and turning complex 3D surfaces
Answer: b
Explanation: Low voltage decreases the equilibrium machining gap and results in a better surface finish and finer tolerance control. Voltage across the cutting gap influences the current and the MRR and is controlled in most ECM operations. Increased current leads to electrolyte heating – low temperature of the electrolyte is conducive for a better surface finish and tolerances.
13. Which of the following largely affects the MRR?
a) ECM cell size
b) Tool shape
c) Feed rate
d) Complexity of the product
Answer: c
Explanation: Feed rate determines the current passed between the tool and the work. High feed rate results in higher MRR. High feed rates also decrease the equilibrium machining gap resulting in improvements of the surface finish and tolerance control. At slower feed rates, the MRR decreases as the gap increases resulting in the rise of resistance and drop in the current.
14. Conductivity of the solution can be increased by_____
a) increasing the gap between the tool and the workpiece
b) increasing the temperature of the solution
c) increasing the concentration of the solution
d) using conductive workpiece
Answer: c
Explanation: Electrolyte conductivity can be increased in following ways-
• Increasing the concentration will cause conductivity to rise
• Temperature increases of the electrolyte also increases conductivity
Low concentration and low temperature will results in lower MRR. Electrolyte conductivity affects the resistance across the gap, but the gap doesn’t affect the conductivity of the electrolyte.
15. The velocity and the electrolyte flow through the gap is also an important parameter affecting the surface finish and MRR.
a) True
b) False
Answer: a
Explanation: If the velocity is too low, the heat and by-products of the reaction build in the gap causing non-uniform material removal. A velocity that is too high will cause cavitation, also uneven material removal.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electro-Chemical Machining – 4”.
1. What does faraday’s second law electrolysis state?
a) W∝Q, where W= mass of substance deposited and Q= charge passed through the electrolyte
b) w1/w2 = E1/E2, where w1 and w2 = mass of different substances deposited, and E1 and E2 = their equivalent masses
c) Induced EMF = – dΦ / dt
d) Force between two charge particles q1 and q2, F= kq1q2/r2
Answer: b
Explanation: Faraday’s second law of electrolysis states that, when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalent or equivalent weight.
2. What is faraday’s first law of electrolysis?
a) W∝T, where W= mass of substance deposited and T= temperature of the electrolyte
b) W∝K, where W= mass of substance deposited and K= ionisation constant of the electrolyte
c) W∝Q, where W= mass of substance deposited and Q= charge passed through the electrolyte
d) W∝ 1/Q, where W= mass of substance deposited and Q= charge passed through the electrolyte
Answer: c
Explanation: Faraday’s First Law of Electrolysis states that, the chemical deposition due to flow of current through an electrolyte is directly proportional to the quantity of electricity passed through it. i.e., mass of chemical deposition.
3. In ECM, accuracy of the product is independent of the accuracy of the cathode tool.
a) True
b) False
Answer: b
Explanation: The accuracy of the tool shape directly affects the work piece accuracy, since configuration of the cavity produced cannot be more accurate than the tool the produces it.
4. Which of the following materials can be used for making cathode tool?
a) Monel
b) Cast iron
c) Lead
d) Carbides
Answer: a
Explanation: The materials the find wide applications in the manufacture of tools for ECM are aluminium, brass, bronze, copper, carbon, stainless steel, monel and reinforced plastics. All these materials are easy to machine.
5. Conductivity of the electrolyte is unaffected by the loss of hydrogen during electrolysis.
a) True
b) False
Answer: b
Explanation: Loss of hydrogen reduces the electrical conductivity of the electrolyte. Also due to loss of water by evaporation or being carried off by hydrogen gas generated, concentration of the solution increases which affects viscosity and electrical conductivity.
6. Which of the following manufacturing process is favourable for making tool for ECM?
a) Casting
b) Cold forging
c) Laser cutting
d) Shaping
Answer: b
Explanation: Shaping the tool is usually not a problem since all the materials are easy to machine. Cold forging and electroforming are favourable methods of tool making.
7. Precipitate formation reduces the conductivity of the electrolyte solution.
a) True
b) False
Answer: a
Explanation: Precipitate formation increases the effective viscosity and interferes with the process in the work-electrode gap. Also, salt absorption by the precipitate reduces the concentration, thus reduces the conductivity.
8. Solubility of the reaction products increases with_____
a) increase in pressure of the electrolyte
b) increase in temperature of the electrolyte
c) increase in work-tool gap
d) decrease in temperature of the electrolyte
Answer: b
Explanation: The solubility of the products of the reaction increases with rising electrolyte temperature. Also, increase in temperature of the electrolyte speeds up the electrode reaction and reduces the over-voltages required.
9. In order to obtain good results in ECM, _____
a) maximise polarization
b) allow rise in temperature of the electrolyte
c) removal of used electrolyte form the working gap
d) decrease the concentration of the electrolyte
Answer: c
Explanation: In order to obtain good results, it is essential to
i. remove the contaminated electrolyte from the working gap,
ii. minimize polarization,
iii. limit the rise in temperature of the electrolyte when working at higher current densities.
10. Increase in pressure of the electrolyte above atmospheric pressure is beneficial.
a) True
b) False
Answer: a
Explanation: Increased pressure of the electrolyte above atmospheric pressure increases the boiling point of the electrolyte point of the electrolyte, reduces the over-voltage required at the tool surface and decreases the volume of generated hydrogen due to which it displaces less electrolyte permitting the use of higher current densities.
This set of Manufacturing Processes Questions and Answers for Experienced people focuses on “Electro-Chemical Machining – 5”.
1. There is a huge change in the mechanical properties of the material after ECM.
a) True
b) False
Answer: b
Explanation: There is no appreciable change in the mechanical properties, such as tensile strength, yield strength, hardness, ductility, etc. of the material due to ECM. Values of notch-tensile strength, notched-sensitivity, and the sustained-load characteristics of the ECM parts are comparable with those of conventionally machined parts.
2. _____ strength of stainless steel decreases when machined by ECM.
a) Yield
b) Tensile
c) Fatigue
d) Notched-tensile
Answer: c
Explanation: Fatigue strength of stainless steel is found to decrease by ECM. This can, however, be overcome by cold working the surface of the product after ECM.
3. In ECM, electrode or tooling cost is fixed because_____
a) there is little wear of the tool
b) tool can be used only once
c) tool can be regenerated
d) one tool can be used for any product
Answer: a
Explanation: Electrode or tooling cost is fixed because there is little wear of the ECM tool. There occurs, however, a negligible abrasion wear of electrode due to electrolyte flow across the gap.
4. Sharp change in tool geometry or sharply divergent flow path affects the surface finish of the product.
a) True
b) False
Answer: a
Explanation: Sharp change in tool geometry or divergent flow path causes cavitation which further leads to small irregular raised area, often with bright work area. This can be avoided by reducing electrolyte supply pressure, blending out sharp radii on tool, or by increasing tool feed.
5. Striation, ripples on work surface occur because of ____
a) differential machining of material phases
b) incorrect tool alignment
c) cavitation
d) electrical field concentration of machining current
Answer: a
Explanation: Differential machining of material phases causes striation and ripples on the work surface which leads to poor surface finish. It can be minimised by increasing electrolyte supply pressure, reducing tool feed rate, or by reducing the voltage to maintain the same gap.
6. Foreign particle in electrolyte or insulation failure within tool can cause_____
a) random inaccuracy in work
b) ripples on work
c) cavitation
d) spark damage to work
Answer: d
Explanation: Foreign particle in electrolyte or insulation failure within tool causes spark damage to the tool or work at the point near to electrolyte entry into machining gap. To avoid this, check internal filters, electrolyte ducts, seals and joints. Also check insulation of the tool frequently.
7. Composition of a Nickel superalloy is as follows: Ni = 70.0%, Cr = 20.0%, Fe = 5.0% and rest Titanium. What will be the rate of dissolution if the area of the tool is 1500 mm2 and a current of 1000 A is being passed through the cell? Assume dissolution to take place at lowest valency of the elements.
A Ni = 58.71 ρ Ni = 8.9 ν Ni = 2
A Cr = 51.99 ρ Cr = 7.19 ν Cr = 2
A Fe = 55.85 ρ Fe = 7.86 ν Fe = 2
A Ti = 47.9 ρ Ti = 4.51 ν Ti = 3
a) 2.14 cc/min
b) 3.14 cc/min
c) 4.25 cc/min
d) 1.66 cc/min
Answer: a
Explanation: Now,
ρalloy = 1/ (Σα i / ρ i ), where α i = % of the respective element in the alloy
= 8.07 gm/cc ρ i = density of respective element
Now, MRR = I/ [Fρ*(Σα i ν i )] where F= 96500 coulomb
= 0.0356 cc/sec
= 2.14 cc/min.
8. Discrepancies are sometimes observed between theoretical and actual metal removal rates and electrode feed rates.
a) True
b) False
Answer: a
Explanation: In practise, metal removal rates are often higher than the estimated ones because;
The exact valency at which a metal behaves in the reaction is generally unknown.
ECM continuously exposes a new and clean surface to the electrolyte which is easily attacked chemically. It also varies with electrolyte used and metal being machined.
9. There is a limit to the minimum cross-section of the current carrying parts.
a) True
b) False
Answer: a
Explanation: To prevent over-heating, there is a limit to the minimum cross-section of the current carrying parts. For 1000 A, it is about 6 cm 2 for copper, 25 cm 2 bronze and brass, and 250 cm 2 for stainless steel.
10. Which of the following is suitable if work surface finish is important?
a) High machining voltage
b) High concentration
c) Larger gap
d) High current
Answer: a
Explanation: If work surface finish is important, high machining voltage, dilute electrolyte and a small gap between the workpiece and the tool should be employed instead of low voltage and concentrated electrolyte.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 1”.
1. Etching refers to the removal of material from ___________
a) the soft surface
b) the hard surface
c) the sticky surface
d) the wafer surface
Answer: d
Explanation: Etching refers to the removal of material from the wafer surface. The process is usually combined with lithography in order to select specific areas on the wafer from which material is to be removed.
2. Deposition is a complimentary process to etching.
a) True
b) False
Answer: a
Explanation: The complementary process to etching is deposition , where new material is added. Unlike oxidation , where the underlying Si is consumed to form the oxide layer, in deposition, new material is added without consuming the underlying wafer.
3. In wet etching material is removed by ___________
a) absorption
b) sublimation
c) chemical reaction
d) the force exerted due to flow of solvent
Answer: c
Explanation: A controlled portion of the wafer surface is exposed to the etchant which then removes material by chemical reaction.
4. ________________ is used to protect the remaining area of the wafer while machining.
a) Tin foil
b) Wood
c) Photoresist layer
d) Sodium bicarbonate
Answer: c
Explanation: There is a chemical reaction between the wafer surface and the etchants that helps in material removal. Either a photoresist layer or a hard mask like oxide or nitride layer is used to protect the rest of the wafer.
5. The time for etching is independent of material to be removed.
a) True
b) False
Answer: b
Explanation: The time for etching depends on the amount and type of material that needs to be removed. KOH is a common etchant used to remove Si.
6. Wet etching is used for removal of material from large areas.
a) True
b) False
Answer: a
Explanation: Wet etching is used for removal of material from large areas µ. For smaller areas, where greater precision in the removal of material is required, dry etch is preferred.
7. The wet etching process is ___________
a) isotropic
b) anisotropic
c) isotropic for few materials
d) isobaric process
Answer: b
Explanation: The wet etching process is anisotropic i.e. the etch rate depends on the plane of the atoms in the material, from which atoms are being removed.
8. Incomplete etch occurs due to ___________
a) high concentration of the chemicals
b) high pressure
c) insufficient temperature
d) low chemical activity
Answer: c
Explanation: In incomplete etch, the time is not sufficient for complete material removal. This is usually due to concentration or temperature not being sufficient. The concentration profile left behind is usually a rough surface, due to local variations in material removal.
9. Product after etching of Si wafer with KOH is ______________ shape.
a) square
b) circular at the end
c) trapezoidal
d) oval
Answer: c
Explanation: Because of the difference in the etch rates of Si along the different crystallographic layers the final profile is trapezoidal, with the angle determined by the etch rates.
10. In case of over-etching, material under protective layer gets removed.
a) True
b) False
Answer: a
Explanation: When the etch time is larger than the required etch time, due to isotropic etching, material under the photoresist can get removed. This is called over etching and in extreme cases, it can also lead to liftoff the resist layer.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 2”.
1. Etching process should be selective to the material that has to be removed.
a) True
b) False
Answer: a
Explanation: Etching process should be selective to the material that has to be removed because this helps to protect the material under the mask and also the mask material itself .
2. _______________ is commonly used as a mask for Si etching.
a) Silicon dioxide
b) Silicon nitride
c) Silicone gel
d) Silicon sulphate
Answer: b
Explanation: If silicon nitride is used as mask, its etch rate, under the same conditions, is 1 nm/hr., nearly 10 5 times slower than the etch rate for Si at 90 °C using 30 % KOH which is ~ 100 µm/hr. Thus, silicon nitride is commonly used as a mask for Si etching .
3. The etching rate and time are crucial to prevent over etching.
a) True
b) False
Answer: a
Explanation: The etching rate and time are crucial to prevent over etching since resist removal can cause damage to portions of the wafer that have to be protected from the etchant.
4. Silicon dioxide etch rate at 90 °C using 30 % KOH is approximately ______________
a) 1 µm/hr
b) 5 µm/hr
c) 10 µm/hr
d) 100 µm/hr
Answer: a
Explanation: Silicon dioxide etch rate at 90 °C using 30 % KOH is ~ 1 µm/hr. So, using silicon oxide as a mask for Si etching will not be good enough or a very thick oxide layer is required.
5. For silicon oxide etching, usually ______________ is used.
a) nitric acid and hydrofluoric acid
b) mixture of HF and ammonium fluoride
c) H 3 PO 4
d) Mixture of HPO 4 , HNO , Acetic acid, water
Answer: b
Explanation: For silicon oxide etching, usually a mixture of HF and ammonium fluoride (NH 4 F) is used, that produces a etch rate of ~0.1 µm/hr at room temperature. This mixture does not etch Si, so it provides very good selectivity.
6. For ____________ usually a strong acid like hot phosphoric acid is used at high temperatures.
a) silicon carbide
b) poly Si
c) silicon nitride
d) aluminium
Answer: c
Explanation: For silicon nitride, usually a strong acid like hot phosphoric acid is used at high temperatures since it is a very good passivating layer and hard to remove under normal conditions.
7. Dry etching produces more vertical side walls compared to wet etching.
a) True
b) False
Answer: a
Explanation: Dry etching, as the name suggest, is a removal of material in the absence of solvent. Because of the anisotropic nature of etching, dry etching produces more vertical side walls compared to wet etching, but the removal rate is slower.
8. In dry etching ______________ are used for removing material.
a) solvent etchants
b) gaseous etchants
c) carbide tools
d) powder etchants
Answer: b
Explanation: Dry etching is removal of material in the absence of solvent. Here, etchant gases are the primary medium for the removal of material. There are three main types of dry etching-
1. Plasma etch
2. Ion beam milling
3. Reactive ion etch.
9. In plasma etch, the chemical etchant is introduced in the gas phase.
a) True
b) False
Answer: a
Explanation: In plasma etch, the chemical etchant is introduced in the gas phase. For etching silicon oxide, CF4 is used. The chamber is first evacuated before introducing the gas. Radio frequency electrodes are then used to generate the plasma that ionizes the gas.
10. Plasma etching provides poor thickness control.
a) True
b) False
Answer: b
Explanation: In plasma etching, the ionised gas attacks the oxide layer, removing the layer. Etch rates in plasma etch are ~1—10 µm/hr, much smaller than wet etching. So, it is more suitable for thin layers, but it also provides greater thickness control.
This set of Manufacturing Processes Interview Questions and Answers focuses on “Roll Forming – 2”.
1. EP 2 grease, high-temperature grease and chain and open-gear grease are used in roll forming equipment.
a) True
b) False
Answer: a
Explanation: EP 2 grease is used lubricating gears. This gear can handle heavy, suddenly applied loads in bearing application. High-temperature grease is used in weld boxes and other equipment that is subjected to a temperature above 200°F. Chain and open-gear grease are used on chain couplings, chain-driven components and open gear drives.
2. Which of the following oils is used in roll forming equipment?
a) SAE 140
b) SAE 30
c) Linseed oil
d) SAE 5W-30
Answer: a
Explanation: ISO grade 460 Gear oil is used in sealed gearboxes. Gear oil has extreme pressure additives that strengthen the non-detergent oils to withstand heavy loads found in gears and gear drive systems.
3. In how many types roll forming lubricants are categorised?
a) 3
b) 5
c) 6
d) 4
Answer: b
Explanation: The different types of roll forming lubricants are listed below:
1. Evaporator compounds or vanishing oils
2. Chemical solutions
3. Micro-emulsions
4. Macro-emulsions
5. Petroleum based lubricants.
4. Chemical solutions ideal for coated steel.
a) True
b) False
Answer: a
Explanation: Chemical solutions are one of the fastest growing roll forming lubricant family. They are economical, environmentally safe, easy to handle, and are ideal for use on coated, galvanised, cold roll steel, aluminium, and in some instances, stainless steel.
5. Which of the following is used for lubrication in heavy-duty roll forming?
a) Extreme pressure-type solutions
b) Soap-type solutions
c) Non-ionic type solutions
d) Micro-emulsions
Answer: b
Explanation: The soap-type solutions are used for heavy-duty roll forming. Non-ionic type solutions are excellent for roll forming aluminium and coated components and extreme pressure-type are used for high strength alloys.
6. For which of the following materials evaporative lubricants are used?
a) Hot rolled steel
b) Stainless steel
c) Ferrous and non-ferrous materials
d) Aluminium
Answer: c
Explanation: Evaporative lubricants are used for roll forming of painted, coated, and vinyl surfaces as well as ferrous and non-ferrous materials. They are applied using the proper type of airless spray system.
7. Which of the following is ideal for lubrication in roll forming of hot rolled and cold rolled steel?
a) Micro-emulsion
b) Macro-emulsion
c) SAE 120
d) SAE 20W 40
Answer: a
Explanation: micro-emulsions provide some film strength from the combination of emulsifiers, water-soluble corrosion inhibitors, wetting agents, organic and inorganic salts, and sometimes extreme pressure agents.
8. Macro-emulsions are also called as soluble oils.
a) True
b) False
Answer: a
Explanation: Macro-emulsions contain an oil-based lubricant, such as a mineral or compounded oil in the form of suspended droplets, which have been dispersed with emulsifiers due to which they become milky white appearance. Therefore, they are sometimes misleadingly called soluble oils.
9. Why additives are mixed with lubricating oil?
a) To reduce the friction
b) To increase the heat transfer
c) To change the colour
d) To improve the lubricant properties
Answer: d
Explanation: Additives are mixed to adjust the lubricants and make the suitable for a specific application. Additives improve lubricant’s properties, protect metal surfaces as well as perform many other functions.
Examples of additives: Rust and corrosion additives, EP additives, etc.
10. Pick the odd one out.
a) Sulphur compounds
b) Nitrates
c) Phosphorous compounds
d) Chlorine compounds
Answer: b
Explanation: Nitrates are usually used as rust or corrosion inhibitors; whereas compounds of sulphur, chlorine and phosphor are extreme pressure additives.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 4”.
1. In reactive ion etching, argon gas is ionized by bombarding with electrons.
a) True
b) False
Answer: a
Explanation: Ar gas is introduced into the vacuum chamber where they are ionized by bombarding with electrons. These ions are then directed on to the wafer where they remove material by physical bombardment.
2. In deposition process, material is added unlike etching where material is removed.
a) True
b) False
Answer: a
Explanation: The deposition process is the opposite of etching. Here, material is added to the wafer surface. The layers different from grown layers like oxide and nitride, where the underlying Si is consumed during a high temperature furnace process.
3. Which of the following does not hold true?
a) In epitaxial layers, poly Si is grown using deposition
b) For making trench capacitors deposited films are used
c) Deposited layers can also be used as passivation layers
d) Deposition is same as etching
Answer: d
Explanation: Some of the layers, where deposited films are used, are
Epitaxial layers – usually poly Si is grown for use as a gate.
Dielectric layers – intermetallics
Trench capacitors
Intermetal conducting plugs
Metal layers – conductors
Passivation layers.
4. In deposition, the Si from the wafer is consumed.
a) True
b) False
Answer: b
Explanation: In deposition, the Si from the wafer is not consumed and the wafer can be maintained at room temperature or at elevated temperatures.
5. How many deposition techniques are there?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: There are two main growth techniques-
Physical deposition
Chemical deposition
Depending upon few parameters, the deposition method is selected.
6. Which of the following has no role in selecting the type of growth technique?
a) Thickness of the film
b) Stress on the film
c) Temperature of the film
d) Purity of the film
Answer: c
Explanation: There are some important _lm parameters, which need to be controlled and these decide the type of growth technique that is adopted.
Thickness and uniformity
Roughness
Composition control
Stress
Purity
Film integrity.
7. In case of deep holes/grooves the choice of technique plays an important role.
a) True
b) False
Answer: a
Explanation: In most cases, the underlying substrate is not at. The choice of technique becomes especially important when depositing in deep trenches/holes, with a high aspect ratio that needs to be maintained.
8. For which of the following physical deposition technique is not suitable?
a) Deep trenches
b) Flat surfaces
c) Wafer of very reactive material
d) Rough surfaces
Answer: a
Explanation: In case of deep trenches/holes, aspect ratio needs to be maintained. In such cases, physical deposition techniques will not work since they will cover the hole before filling it.
9. In chemical vapour deposition, chemicals containing the desired film/layer are used.
a) True
b) False
Answer: a
Explanation: the basic principle is that chemicals containing the desired film/layer are introduced into a reactor in the form of a vapour. These chemicals react on the wafer surface to form the film on the wafer.
10. Low pressure chemical vapour deposition is used to_____
a) increase the purity of the film
b) to reduce the roughness of the film
c) to form thick films
d) to reduce stress on the film
Answer: d
Explanation: CVD process can be in atmospheric conditions or under low pressure . LPCVD is usually used for growing silicon nitride, to reduce the comprehensive stress on the film. For growing atomically thin films, a layer by layer growth process, called atomic layer deposition , is used.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 5”.
1. Electronic grade silicon wafers are produced by Czochralski growth method.
a) True
b) False
Answer: a
Explanation: Typically, electronic grade silicon wafers are produced by Czochralski growth method. In this process, a cylindrical ingot of high purity monocrystalline silicon is formed by pulling a seed crystal from a bath composed of polysilicon.
2. Porous silicon structures are produced by electrochemical etching of silicon wafers in organic solutions of_____
a) acrylonitrile
b) benzene
c) formaldehyde
d) dimethylformamide
Answer: d
Explanation: Typically, porous silicon structures are produced by electrochemical etching of silicon wafers in organic solutions of acetonitrile (CH 3 CN) or dimethylformamide (C 3 H 7 NO) containing hydrofluoric acid .
3. It is mandatory to consider all the safety aspects related to HF handling during etching of Si.
a) True
b) False
Answer: a
Explanation: HF is highly corrosive towards living tissues and its inhalation, ingestion or skin contact are all extremely hazardous and can be lethal. HF should be handled under a hood with proper ventilation, wearing personal HF gas monitor with audible alarm, safety sensor for liquids and proper personal protective equipment such as safety goggles, face shield, chemically resistant butyl rubber gloves and apron.
4. The oxide later formed on commercial Si does not affect the etching of Si.
a) True
b) False
Answer: b
Explanation: The native oxide layer formed on commercial silicon wafers under ambient atmospheric conditions must be removed. The most widespread method to remove this oxide layer is the so-called RCA cleaning process. This process is divided into three steps: namely; removal of organic contaminants, removal of the native oxide layer and removal of ionic contaminations.
5. Which of the following can lead to broken porous silicon samples?
a) High current density
b) High concentration of electrolyte
c) Inappropriate design of cell
d) High temperature of the cell
Answer: c
Explanation: An inappropriate design of the cell can lead to broken samples, leaky set-ups and corroded contacts. Note that aspects such as materials, contacts and sealants are critical in the design of the electrochemical cell used to produce porous Si by electrochemical or chemical etching approaches.
6. Cell material must be resistant to HF solution.
a) True
b) False
Answer: a
Explanation: since most common acid electrolytes used to prepare porous Si are HF-based solutions, the materials of choice used to fabricate the body of the etching cells are resistant to HF. The most representative examples of these are polyvinyl chloride and polytetrafluoroethylene .
7. Which of the following materials is suitable for making sealant while working with HF based solutions?
a) Silicone rubber
b) Polyurethane
c) PVC
d) Acrylonitrile-butadiene copolymer
Answer: d
Explanation: Sealants are standard black O-rings made of acrylonitrile-butadiene copolymer or vinylidene fluoride-hexafluoropropylene are preferred as they are stable in HF at concentrations up to 50 %.
8. Which of the following materials is the better choice for making conductors in cells used to produce pSi by electrochemical etching?
a) Nickel
b) Gold
c) Copper
d) Vanadium
Answer: b
Explanation: It is critical to consider the resistance of the metal used as a contact towards corrosion since a continuous exposure to the etching electrolyte can degrade its integrity with use and thus its performance. Typically, noble metals such as platinum or gold are the best choice as they are inert. Other materials such as stainless steel, brass, tungsten or aluminium can also be used.
9. Hydrogen-terminated silicon surfaces are ____________
a) hydrophobic
b) hydrophilic
c) hydropic
d) deliquescent
Answer: a
Explanation: After the cleaning step and immersion in HF solutions, the silicon wafer surface is terminated with hydrogen atoms . Hydrogen-terminated silicon surfaces are hydrophobic, showing a large contact angle for a drop of water [34, 35]. Silicon surfaces dipped in HF or an ammonium fluoride show equivalent hydrophobic character.
10. Roughness of the hydrophobic surfaces formed after dipping silicon in HF solution is dependent on the type of etchant.
a) True
b) False
Answer: a
Explanation: The roughness of these surfaces is highly dependent on the chemical treatment and type of etchant used. While NH4F provides atomically flat surfaces for and oriented silicon surfaces, a treatment with HF creates surfaces with nanometric roughness.
This set of Manufacturing Processes test focuses on “Electrochemical Etching – 6”.
1. Which of the following is true about chemical dissolution of hydrogen-terminated silicon in HF based solutions.
a) Si atoms are replaced by F atoms
b) H atoms are replaced by F atoms
c) F− ions are replaced by Si atoms
d) H atoms are replaced by F− ions
Answer: d
Explanation: As far as the chemical dissolution of hydrogen-terminated silicon is concerned, this process requires the replacement of superficial H atoms by fluoride ions , which are incorporated from the etching electrolyte solution.
2. To create a neutralized Si–F bound, an electronic hole (h + ) is generated.
a) True
b) False
Answer: a
Explanation: Under open circuit conditions, the silicon surface remains passivated. Therefore, an electronic hole (h + ) must be generated to create a neutralized Si–F bound. The Si–F bound can be created under certain anodic bias by the polarisation effect induced by the F atom over the Si atom.
3. Si + 4HF 2 — + h + -> SiF 6 2- + 2HF + _____ + e — . Complete the reaction for dissolution of hydrogen-terminated Si in HF based solution.
a) F 2
b) SiF 4
c) H 2
d) Si-H
Answer: c
Explanation: A new F− atom bounds the Si atom at a different position and a gas hydrogen molecule (H 2 ) is generated. The progressive repetition of this process weakens the Si–Si bounds by the strong electronegativity of F atoms through nucleophilic attack. In this way, Si atoms are etched away by reaction with HF and pores are generated.
4. In the fabrication of pSi structures, wet chemical etching with alkaline etchants is used.
a) True
b) False
Answer: a
Explanation: An important aspect in the fabrication of pSi structures is the use of wet chemical etching with alkaline etchants, which are mainly used for chemical polishing or anisotropic etching of silicon. These pre- and post-treatments make it possible to design and engineer a broad range of pSi structures.
5. Which of the following alkaline etchant is most widely used to etch silicon?
a) Tetramethyl ammonium hydroxide
b) Aluminium hydroxide
c) Calcium hydroxide
d) Formaldehyde
Answer: a
Explanation: The most widespread alkaline etchants used to etch silicon are potassium hydroxide and tetramethyl ammonium hydroxide , although other inorganic and organic compounds such as lithium hydroxide , sodium hydroxide , rubidium hydroxide , caesium hydroxide (C s OH), ammonium hydroxide (NH 4 OH), cholin and ethylenediamine have been used as well.
6. Etching rate of silicon is independent of the crystal planes.
a) True
b) False
Answer: b
Explanation: The etching rate of silicon in these etchants is highly dependent on the crystal planes, the doping level of the silicon crystal and the etchant concentration and its temperature.
7. Porous materials are classified according to_____
a) total area
b) difference between initial and final mass
c) pore size
d) manufacturing method
Answer: c
Explanation: Following the International Union of Pure and Applied Chemistry nomenclature used to classify porous materials as a function of their pore size .
8. In how many categories porous silicon can be divided?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: pSi structures can be divided into three categories: microporous silicon with dp < 2 nm, mesoporous silicon with 2 nm < dp < 50 nm and macroporous silicon with dp > 50 nm.
9. According to morphological details, pSi can be divided as sponge-like pSi and pSi featuring cylindrical pores.
a) True
b) False
Answer: a
Explanation: pSi can present a variety of morphological details, these can be divided into two main categories: sponge-like pSi, which features densely and randomly distributed branched pores and pSi featuring cylindrical pores, which can have rough or smooth walls. While μpSi and mpSi structures feature sponge-like morphology, MpSi structures have cylindrical pores.
10. MpSi structures have a random distribution of pores.
a) True
b) False
Answer: a
Explanation: As far as the spatial distribution of pores, MpSi structures present a random distribution. However, these structures can be produced featuring a perfectly ordered spatial distribution of pores. To this end, the surface of the silicon wafer must be patterned by lithographic techniques before the electrochemical etching process is carried out.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 7”.
1. Morphology of μpSi and mpSi can be defined by a concrete spatial distribution.
a) True
b) False
Answer: b
Explanation: The sponge-like morphology of μpSi and mpSi cannot be defined by a concrete spatial distribution because of the complex structure of their porous network.
2. The resulting pore structure in pSi is intrinsically dependent on the doping level of the Si wafer.
a) True
b) False
Answer: a
Explanation: MpSi is produced by electrochemical etching of n-type wafers. The etching of p- and n-type Si wafers with a high or moderate level of doping yields mpSi structures and μpSi structures.
3. Why the pore characteristics of the resulting pSi structures depend upon the doping type? Choose the most correct option.
a) Processing time depends on doping
b) The manufacturing process is selected on the basis of doping
c) The pore formation mechanism relies on doping
d) Atomic size of doping atom affects the final structure
Answer: c
Explanation: The reason why the pore characteristics of the resulting pSi structures depend upon the doping type and its level of the silicon wafer is that the pore formation mechanism relies on these parameters.
4. _____ mechanism is associated with the pore formation in μpSi structures.
a) Enhanced electric field
b) Tunnelling
c) Quantum confinement
d) Space-charge limited mechanism
Answer: d
Explanation: The space-charge limited mechanism is associated with the pore formation in μpSi structures, which results when n-type silicon wafers are electrochemically etched in HF solutions.
5. The enhanced electric field and tunnelling mechanisms are associated with the formation of _____ structures.
a) mpSi
b) MpSi
c) μpSi
d) pSi
Answer: a
Explanation: The enhanced electric field and tunnelling mechanisms are associated with the formation of mpSi structures when highly or moderately doped Si wafers are electrochemically etched in HF solutions.
6. In the pore formation mechanism of MpSi, electronic holes initiate the dissolution process of silicon.
a) True
b) False
Answer: a
Explanation: As far as the pore formation mechanism of MpSi is concerned, electronic holes initiate the dissolution process of silicon and these are minority charge carriers in n-type silicon. Therefore, the concentration of electronic holes in n-type silicon under equilibrium conditions is very low.
7. The neutral state is achieved when the concentration of electrons is equal to the concentration of electronic holes and ionized donors.
a) True
b) False
Answer: a
Explanation: Three types of charges are present in the bulk silicon: namely, electronic holes, electrons and ionized donors. The system is a neutral state when the concentration of electrons is equal to the concentration of electronic holes and ionized donors together.
8. For a given level of doping, the growth of MpSi in n-type silicon substrates can be controlled by_____
a) amount of electric current passed
b) current density
c) voltage drop
d) processing time
Answer: b
Explanation: For a given level of doping, the growth of MpSi in n-type silicon substrates can be led by the current density and the illumination applied in the course of the etching process.
9. A pre-treatment by a lithographic patterning stage enables the production of ordered pore distribution.
a) True
b) False
Answer: a
Explanation: As-produced MpSi has a random pore distribution since pores nucleate uniformly on the Si wafer surface. A pre-treatment by a lithographic patterning stage enables the production of MpSi structures with perfectly ordered pores featuring square or triangular arrangement.
10. Among all the etching parameters, the etching current density is the most critical factor.
a) True
b) False
Answer: a
Explanation: The growth of well-defined cylindrical macropores from top to bottom in MpSi can be precisely controlled through the etching parameters . In particular, among these parameters, the etching current density is a critical factor to lead a homogeneous pore growth as the longer the pore the more effective the collection of photo-generated holes.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 8”.
1. Cone-like pores can be obtained by using Lehmann’s law.
a) True
b) False
Answer: a
Explanation: According to the Lehmann’s law, the increasing collection of photo-generated holes results in a progressive reduction of the pore diameter with depth, yielding cone-like pores with decreasing diameter from top to bottom.
2. Progressively modified illumination intensity approach can be used to develop some optical structures.
a) True
b) False
Answer: a
Explanation: This approach can be readily used to develop some optical structures such as photonic crystals and optical waveguides in the visible and NIR range as the refractive index of MpSi can be engineered in depth along the pore yielding a waveguide structure embedded in the array of macropores.
3. Progressively modified illumination intensity approach when combined with lithographic patterning, gives_____
a) straight macropores
b) straight micropores
c) sponge-like pSi
d) honeycomb like pattern
Answer: a
Explanation: Variable illumination intensity technique can be combined with lithographic patterning to produce 2D infrared photonic crystals featuring perfectly ordered and straight macropores.
4. In the technique mentioned in the previous question, arrays of macropores are _____
a) heated to the melting temperature
b) soaked in HF solution for several hours
c) coated by a lithographic mask
d) kept under UV rays
Answer: c
Explanation: In this process, arrays of macropores are coated by a lithographic mask after electrochemical etching. Next, MpSi is selectively removed from the unmasked areas by a wet chemical etching. This results in a set of deep bars of macropore rows with well-defined pore geometry.
5. Which of the following is true according to the Lehmann’s model for the formation of MpSi?
a) The current density is equal to the critical current density
b) The current density is half of the critical current density
c) The critical current density is equal to square of the current density
d) Lehmann’s model does not give relation between current density and critical current density
Answer: a
Explanation: According to the Lehmann’s model for the formation of MpSi, the current density at the pore bottom tips is equal to the critical current density. Therefore, an increment of the illumination intensity at the backside of the silicon wafer during etching leads to the generation of electronic holes, which directly contribute to the total current density.
6. The pore diameter in macroporous silicon can be periodically modulated.
a) True
b) False
Answer: a
Explanation: Following the approach based on the Lehmann’s model, the pore diameter in macroporous silicon can be periodically modulated . This approach takes advantage from the fact that the porosity of the resulting MpSi structure is established by the ratio between the total current density and the critical current density .
7. Increase in the total current density produced by the generation of electronic holes increases the pore diameter.
a) True
b) False
Answer: a
Explanation: The critical current density is constant at the pore bottom tips and thus the increment of the total current density produced by the generation of electronic holes widens the pore diameter. Following this procedure, the pore structure of MpSi can be modulated to produce periodic ratchet-type or circular pore modulations.
8. If the etching conditions are not controlled, then _____ decreases with pore depth.
a) the period length
b) diameter of the pores
c) orderliness of the pores
d) reflectivity of the material
Answer: a
Explanation: If the etching conditions are not controlled, the period length, which is defined as the distance between two consecutive pore modulations, decreases with the pore depth due to diffusion limitations . As a result, the critical current density decreases and the pore growth rate becomes slower.
9. Post-treatment starts with a thermal treatment of the MpSi structure at _____
a) 900°C
b) 1100 °C
c) 1570°C
d) 1650°C
Answer: b
Explanation: A post-treatment is required after the fabrication of MpSi. This post-treatment starts with a thermal treatment of the MpSi structure at 1100 °C for 100 min under oxygen atmosphere.
10. During post treatment of MpSi, a layer of silicon dioxide is formed.
a) True
b) False
Answer: a
Explanation: A thermal treatment of the MpSi structure at 1100 °C for 100 min under oxygen atmosphere generates a silicon dioxide layer of 200 nm along the inner surface of the pores of MpSi.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 9”.
1. Bending curvature of silicon wafers varies ______ with the specific area of the MpSi structure.
a) linearly
b) inversely
c) cubically
d) it not affected by specific area
Answer: a
Explanation: The structure of MpSi can result broken by oxide-induced stress in the course of this stage. Thinner MpSi layers minimise this problem since the bending curvature of silicon wafers relies linearly on the specific area of the MpSi structure.
2. Silicon oxide layer can be removed using HF solution.
a) True
b) False
Answer: a
Explanation: The silicon oxide layer is selectively removed from the backside of the silicon wafer by a wet chemical etching in a buffer HF solution . Finally, the remaining silicon is etched away by a wet chemical etching in a solution of TMAH 25 % wt at 85 °C.
3. Length of the silicon dioxide pillars is dependant on the etching time and the pore length.
a) True
b) False
Answer: a
Explanation: Silicon is etched away by a wet chemical etching in a solution of TMAH. After that, a new structure based on silicon dioxide micropillars rises from the backside of the wafer as the silicon dioxide layer covering the pore walls is not etched by TMAH. The length of the resulting silicon dioxide pillars can be established by the etching time and by the pore length in the MpSi structure.
4. Lithographic technique can be used for patterning the Si wafer.
a) True
b) False
Answer: a
Explanation: The backside of the silicon wafer can be patterned by lithographic methods after the oxidation stage, enabling a selective etching on the wafer backside by TMAH.
5. It possible to produce arrays of silicon dioxide pillars inside _____
a) long pipes
b) spherical cavities
c) truncated pyramids
d) thin shells
Answer: c
Explanation: Given that the etching process in TMAH is selectively performed over these areas without protective mask in an anisotropic manner, the approach makes it possible to produce arrays of silicon dioxide pillars inside truncated pyramids.
6. Arrays of cone-like silicon dioxide pillars can be produced using _____
a) truncated MpSi
b) conical MpSi
c) cylindrical MpSi
d) planner MpSi
Answer: b
Explanation: Arrays of cone-like silicon dioxide pillars can be produced when conical MpSi is used as the starting material. The features of these 3D structures can be precisely controlled by the etching parameters and the features of the lithographic patterning.
7. When the doping density in the silicon wafer is increased, then _____
a) electric field strength is increased
b) width of depletion region is increased
c) hinderance to charge carries is increased
d) quality of the product is increased
Answer: a
Explanation: When the doping density in the silicon wafer is increased, the electric field strength increases, decreasing the width of the depletion region and enabling charge carriers to pass through the space charge region by tunnelling.
8. Avalanche breakdown is the dominant mechanism at high doping densities.
a) True
b) False
Answer: b
Explanation: At high doping densities (i.e. ≥1018 cm −3 ) tunneling mechanism dominates the charge transfer while avalanche breakdown is the dominant mechanism at low doping densities.
9. The electric field strength decreases around the depressions present on the silicon wafer surface.
a) True
b) False
Answer: b
Explanation: The electric field strength increases around the depressions and pits present on the silicon wafer surface. This results in a local reduction of the depletion region width, which increases the tunneling probability of charge carriers, incrementing the local current density.
10. In the beginning of the electrochemical etching, some of these pits present on the surface of the silicon wafer develop into mesopores.
a) True
b) False
Answer: a
Explanation: In the course of the first seconds of the electrochemical etching, some of these pits present on the surface of the silicon wafer develop into mesopores, the density of which across the surface is established by the doping level and the etching conditions.
This set of Manufacturing Processes Puzzles focuses on “Electrochemical Etching – 10”.
1. Pore formation in μpSi is independent of quantum confinement.
a) True
b) False
Answer: b
Explanation: Pore formation in μpSi is a complex phenomenon involving different mechanisms, i.e. quantum confinement, crystallographic face selectivity, tunnelling and enhanced electric field.
2. μpSi structures have _____________
a) high porosity
b) longer life
c) organised pores
d) low density
Answer: a
Explanation: Microporous silicon structures can be obtained by electrochemical etching of p-type silicon wafers. μpSi structures have high porosity and also feature a porous structure with silicon walls of a few nanometres thick separating adjacent micropores.
3. In the quantum confinement model for μpSi structures, energy band gap in the wall region varies.
a) True
b) False
Answer: a
Explanation: The formation of μpSi structures can be explained by the quantum confinement model, in which the energy band gap in the wall region increases as a result of quantum confinement effect, generating an energy barrier for electronic holes.
4. In μpSi structures, depletion of holes is affected by the energy barrier generated in the wall region.
a) True
b) False
Answer: a
Explanation: If the energy barrier in the wall region is bigger than that of the bias-dependent energy of electronic holes, the porous structure is depleted of holes and thus passivated from dissolution during the etching process.
5. The effective medium concept, where the optical properties of the material are established by its ________________
a) pore distribution in the structure
b) band gap
c) pore thickness
d) wavelength of the incident light
Answer: b
Explanation: The interaction of light with mpSi and μpSi structures is explained by the effective medium concept, where the optical properties of the material are established by its band gap. Therefore, the interaction between light and matter in these porous structures can be designed by engineering their effective refractive index.
6. The refractive index of mpSi and μpSi structures has some anisotropy.
a) True
b) False
Answer: a
Explanation: The refractive index of mpSi μpSi structures and presents certain anisotropy along the specific crystallographic axes. This anisotropy, which can range from 1 to 10 %, is associated with the elongated pore shape along the growth direction.
7. The porosity of mpSi and μpSi relies mainly on the ______________
a) thickness of the material
b) current density
c) etching agent
d) temperature
Answer: b
Explanation: The porosity of mpSi and μpSi relies mainly on the current density applied during the etching process. For this reason, multi-layered mpSi and μpSi structures, which consist of stacks of porous silicon layers featuring different levels of porosity, can be produced from top to bottom by modifying the current density in the course of the etching process.
8. μpSi and mpSi structures are widely used to produce optical structure.
a) True
b) False
Answer: a
Explanation: As a result of their geometric and optoelectronic properties, these structures have been extensively used to produce a variety of optical structures such as micro-cavities, distributed Bragg reflectors, waveguides, omnidirectional mirrors and rugate filters.
9. The effective refractive index of pSi can be varied with the current density.
a) True
b) False
Answer: a
Explanation: The effective refractive index of each layer is directly related with the porosity level. So, the effective refractive index of pSi can be engineered in depth by alternating the current density during the etching process.
10. Thickness of layers in the mpSi and μpSi structures can be controlled by_____
a) current density
b) etching agent
c) etching time
d) porosity
Answer: c
Explanation: The thickness of each layer can be precisely controlled by the etching time as the former is directly proportional to the latter. Therefore, the interaction between incident light and matter in mpSi and μpSi structures can be engineered to produce optical nanostructures for a broad range of applications.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 11”.
1. mpSi and μpSi structures are used to develop distributed Bragg reflectors.
a) True
b) False
Answer: a
Explanation: Multilayered mpSi and μpSi structures can be used to develop distributed Bragg reflectors . Basically, a pSi-based DBR structure consists of multiple layers of pSi with different porosity levels and thicknesses.
2. The structure of the mpSi- or μpSi-based DBR affects their refractive indices.
a) True
b) False
Answer: a
Explanation: The interfaces between two consecutive layers of dielectric material reflect incident light due to the effective refractive index contrast. Therefore, constructive light interference can be engineered by designing the structure of the mpSi- or μpSi-based DBR .
3. DBR structures based on_____ can be implemented into Fabry–Pérot filters.
a) mpSi
b) pSi
c) SiO 2
d) graphite
Answer: a
Explanation: DBR structures based on mpSi and μpSi can be implemented into Fabry–Pérot filters, also called optical microcavities, which are composed of two parallel DBRs with a space layer of different effective refractive index in between.
4. The effective optical thickness of the space layer is taken equal to _____
a) frequency
b) wavelength
c) amplitude
d) product of refractive index and density of the material
Answer: b
Explanation: The effective optical thickness of the space layer is typically engineered as the wavelength of the incident light or half of it.
5. Microcavities based on mpSi and μpSi can be used to develop optical pass-band filters.
a) True
b) False
Answer: a
Explanation: The reflectivity spectrum of microcavities based on mpSi and μpSi shows a narrow pass-band centred at the wavelength where the light is reflected with the highest intensity. Therefore, the structural design of microcavities based on mpSi and μpSi makes it possible to develop optical pass-band filters and sensors.
6. The effective refractive index of mpSi and μpSi are modulated to produce rugate filters.
a) True
b) False
Answer: a
Explanation: If the current density profile is modified in a sinusoidal manner in the course of the electrochemical etching, the effective refractive index of mpSi and μpSi can be modulated to produce rugate filters, which are another type of optical structure used in optoelectronic and sensing applications.
7. Which of the following is one of the important optical property of mpSi and μpSi structure?
a) Photo-conductivity
b) Stimulated emission
c) Photo-luminescence
d) Photo-emissivity
Answer: c
Explanation: Another important optical property of mpSi and μpSi structure is their photo-luminescence , which has been extensively studied during the last decades. Bulk crystalline silicon presents a very weak PL peak at 1100 nm.
8. The discovery of bright red-orange photoluminescence was the origin for the use of mpSi materials for optoelectronic devices.
a) True
b) False
Answer: a
Explanation: Photo-luminescence limits the use of silicon to develop optoelectronic devices, which are aimed at converting light into electricity . However, the discovery of bright red-orange photoluminescence and the identification of confinement effects in the absorption spectrum of pSi were the starting point of a flood of studies focused on the development of optoelectronic devices based on mpSi and μpSi structures such as switches, displays and lasers.
9. PL properties of mpSi and μpSi structures depend on _____
a) temperature
b) etching conditions
c) light intensity
d) refractive index
Answer: b
Explanation: PL properties of mpSi and μpSi structures depend on the etching conditions. The different PL bands in pSi can be tuned from blue-green, red-orange to infrared by adjusting the etching conditions.
10. An increment of the current density can lead to blue shifts in the PL peak of mpSi.
a) True
b) False
Answer: a
Explanation: An increment of the current density, a decrease in the concentration of HF or an increase of the illumination intensity lead to blue shifts in the PL peak of mpSi and μpSi. In addition, it is worth stressing that PL in pSi is dependent on the porosity level as well as the doping density.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 12”.
1. Metal-assisted chemical etching approach is widely used to produce pSi structures with precisely defined geometric features.
a) True
b) False
Answer: a
Explanation: Metal-assisted chemical etching of silicon is considered a simple and cost-competitive alternative to conventional electrochemical methods. This approach has been used to produce pSi structures with precisely defined geometric features and characteristics not achievable by other fabrication approaches.
2. _____ can be controlled in metal-assisted etching.
a) Etching rate
b) Etching direction
c) Etching area
d) Etching temperature
Answer: b
Explanation: The etching direction in metal-assisted etching can be controlled on silicon and non- directions to produce pSi structures with slanted growth directions. 100, 110, 111, etc. are miller indices for the orientation of the Si structure.
3. Metal-assisted etching can produce pSi structures with high surface-to-volume ratio.
a) True
b) False
Answer: a
Explanation: Metal-assisted etching enables the fabrication of pSi structures with high surface-to-volume ratio, high crystalline quality and low level of defects.
4. It can be said that metal-assisted etching of silicon is an alternative approach to conventional electrochemical etching methods.
a) True
b) False
Answer: a
Explanation: Metal-assisted etching can produce pSi structures with high surface-to-volume ratio high crystalline quality and low level of defects. In addition, metal-assisted etching makes it possible to produce pSi structures within a broad range of feature sizes, which can range from 5 nm to > 1 μm. For these reasons, metal-assisted etching of silicon has become an alternative approach to conventional electrochemical etching methods.
5. Etching rate is affected by _____
a) temperature
b) pressure
c) coating on Si surface
d) material thickness
Answer: c
Explanation: When a silicon substrate is partly covered by a noble metal and it is immersed in an etchant solution composed of an oxidative agent and HF, the silicon beneath the noble metal is etched at a faster rate than that of the uncovered silicon.
6. Geometric features of the pSi structure are determined by noble metal mask.
a) True
b) False
Answer: a
Explanation: Basically, the geometric features of the resulting pSi structures are established by the noble metal mask. The noble metal sinks into the silicon substrate, producing pores or pillars depending on the etching conditions and the metal features.
7. In metal-assisted etching of pSi, chemical reactions occur between _____
a) noble metal and etching agent
b) silicon and etching agent
c) noble metal and silicon
d) no such reactions occur in metal-assisted etching
Answer: c
Explanation: As far as the mechanisms and reactions involved in the formation of pSi structures produced by metal-assisted etching is concerned, it is well-known that chemical and electrochemical reactions occur near the interface between the noble metal and the silicon substrate when the system is immersed in an etchant composed of HF and H 2 O 2 .
8. In metal-assisted etching of pSi, the noble metal works as a cathode.
a) True
b) False
Answer: a
Explanation: In this system, the noble metal works as a cathode, where hydrogen peroxide is reduced at the metal surface following these electrochemical reactions while the silicon works as the anode:
H 2 O 2 + 2H+ -> 2H 2 O + 2H +
2H + -> H 2 + 2 protons.
9. In the above mentioned method, charge transfer between noble metal and silicon occurs for the oxidation.
a) True
b) False
Answer: a
Explanation: In analogy with chemical etching of silicon, it is accepted that charge transfer between noble metal and silicon occurs for the oxidation and dissolution of the latter by hole injection mechanism.
10. In hole injection mechanism, holes are created in the noble metal.
a) True
b) False
Answer: a
Explanation: In that system, the noble metal plays the role of cathode, where the reduction of the oxidant takes place. Holes generated in the noble metal are then injected into the silicon substrate, oxidising silicon atoms, which subsequently are dissolved by reacting with HF.
This set of Manufacturing Processes Quiz focuses on “Electrochemical Etching – 13”.
1. In metal-assisted etching of porous silicon, the oxidant is reduced at the noble metal surface.
a) True
b) False
Answer: a
Explanation: The oxidant is reduced at the noble metal surface due to its catalytic activity. The reduction of the oxidant generates electronic holes, which are subsequently injected into the silicon substrate through the noble metal interface.
2. Electronic holes in metal-assisted etching of porous silicon oxidise silicon atoms.
a) True
b) False
Answer: a
Explanation: Electronic holes oxidise silicon atoms at the interface noble metal-silicon, which are then etched away by HF molecules. The concentration of electronic holes is maximum at the noble metal-silicon interface and thus its dissolution rate is much faster there.
3. Which of the following is used as an oxidant in metal-assisted etching?
a) Sulphuric acid
b) Nitric acid
c) Oxygen bubbles
d) Peroxy-di-sulfuric acid
Answer: c
Explanation: Regarding the type of oxidant, hydrogen peroxide is the most commonly used although other oxidants such as oxygen bubbles, oxygen dissolved in water, silver nitrate (AgNO 3 ), chloroauric acid (HAuCl 4 ), potassium gold chloride (KAuCl 4 ), chloroplatinic acid (H 2 PtCl 6 ) have been explored as well.
4. The holes which are left out after oxidation of silicon atoms enter the bulk silicon region.
a) True
b) False
Answer: a
Explanation: The remaining electronic holes diffuse from the interface noble metal-silicon to the bulk silicon.
5. The structural features of pSi produced by metal-assisted method independent on illumination.
a) True
b) False
Answer: a
Explanation: The resulting structural features of pSi produced by metal-assisted approach rely on different parameters such as the etchant composition and its temperature, the nature of the noble metal, the illumination and the intrinsic properties of the silicon substrate .
6. Structural features of metal-assisted etched pSi are different for different oxidant.
a) True
b) False
Answer: a
Explanation: The resulting morphologies and structural features of metal-assisted etched pSi differ from one oxidant to another as they can change the morphology of the metal or produce different precipitates in the course of the etching process.
7. Concentration and composition of the etchant electrolyte can affect the features of the etching product.
a) True
b) False
Answer: a
Explanation: Important parameter that directly affects the geometric features of the resulting pSi produced by metal-assisted etching is the concentration and composition of the etchant electrolyte. For instance, etching of silicon wafers coated with platinum particles in an etchant with low concentration of HF : H 2 O 2 :H 2 O = 2:1:8; v:v:v) yields pores with cone-like morphology from top to bottom.
8. At high concentrations of HF, the etching rate is determined by _____
a) oxidant
b) oxidant concentration
c) temperature of the oxidant
d) material to be etched
Answer: b
Explanation: Change of pore morphology and geometric features with the ratio acid/oxidant can be explained by the fact that at high concentrations of HF , the etching rate is determined by the oxidant concentration and the electronic holes generated at the interface noble metal-silicon are rapidly consumed as a result of the excess of HF available to dissolve silicon.
9. The etching rate is determined by the HF concentration when the ratio acid/oxidant is lower than _____
a) 50%
b) 60%
c) 68%
d) 70%
Answer: d
Explanation: When the ratio acid/oxidant is lower than 70 %, the etching rate starts to be determined by the HF concentration. In such a scenario, the generation of electronic holes is higher than their consumption rate and thus the excess of electronic holes diffuse away to the pore walls, where μpSi structures are generated.
10. High concentrations of oxidant result in isotropic etching.
a) True
b) False
Answer: a
Explanation: At high concentrations of oxidant (i.e. 20 % > [HF]/([HF] + [H 2 O 2 ]) > 9 %) electronic holes diffuse massively towards the surface of silicon in contact with HF, resulting in an isotropic etching independent on the silver particles present on the wafer surface.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 14”.
1. The etching rate is also affected by the diffusion of by-products.
a) True
b) False
Answer: a
Explanation: Apart from the ratio between acid and oxidant, the etching rate is also affected by other factors such as the etchant temperature and the diffusion of by-products and etchant through the pores.
2. Bigger pores enable faster etching rates.
a) True
b) False
Answer: a
Explanation: Some studies have demonstrated that bigger pores enable faster etching rates as a result of a more efficient diffusion of etchant and by-products through the pores and the interface noble metal-silicon.
3. Which of the following increases the etching rate?
a) Lower temperature
b) Stirring the etchant
c) Low concentration of the etchant
d) High concentration of the oxidant
Answer: b
Explanation: More efficient diffusion rates can be achieved by stirring the etchant during the etching process. Another important factor directly related with the etching rate is the temperature of the etchant. Etch rate increases with the temperature.
4. In which temperature range the etching rate in metal-assisted etching of silicon increases?
a) 0—32 °C
b) 0—50 °C
c) 20—60 °C
d) Above 50 °C
Answer: b
Explanation: Scientists have demonstrated that the etching rate of silicon nanowires produced by metal-assisted etching of silicon in HF/H 2 O 2 and HF/AgNO 3 increases with the temperature from 0 to 50 °C. Moreover, it was established a linear relationship between the silicon nanowires length and the etching time within the aforementioned range of temperature.
5. Which of the following metals are used in metal-assisted approach to etch silicon?
a) Vanadium
b) Copper
c) Zinc
d) Gold
Answer: d
Explanation: As far as the different aspects associated with the noble metal is concerned, the most typical metals used to etch silicon by metal-assisted approach are silver, gold, platinum and palladium.
6. The noble metals used in metal assisted approach are deposited by thermal evaporation, electroless deposition, etc. techniques.
a) True
b) False
Answer: a
Explanation: These metals can be deposited by thermal evaporation, electroless deposition, electrode position, sputtering, electron beam evaporation, focused ion beam deposition, spin-coating and self-assembly of particles, etc. methods.
7. The metal-assisted etching of pSi structures with lithographic deposition technique produces highly ordered geometric features.
a) True
b) False
Answer: a
Explanation: Some of the deposition methods can be combined with lithography masks generated by micro and nanofabrication techniques. This enables the production of metal-assisted pSi structures with highly ordered geometric features.
8. The resulted pore geometry is the same for all the noble metals.
a) True
b) False
Answer: b
Explanation: When isolated particles are used to produce metal-assisted pSi, the structure, geometric features and morphology of the resulting pSi are dependent on the noble metal. For instance, while Ag or Au particles yield pSi featuring straight pores.
9. Etching through Pt particles can generate straight as well as helical-like pores.
a) True
b) False
Answer: a
Explanation: The pore geometry in pSi produced by etching through Pt particles can vary from well-defined straight pores, helical-like pores or curvy-like pores. Under some conditions, Pt particles move randomly in the course of the etching process, producing complex pSi structures.
10. Etching rate is different for different noble metals.
a) True
b) False
Answer: a
Explanation: The etching rate varies from one noble metal to another. As an example, the etching rate achieved during the etching through Au particles is much slower than that obtained when Pt particles are used.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 15”.
1. Noble metal used in metal-assisted approach affects the formation of μpSi structures on the side walls of pores.
a) True
b) False
Answer: a
Explanation: Another interesting phenomenon dependent on the noble metal is the formation of μpSi structures on the side walls of pores or wires during the etching process. A detailed explanation of the origin of these effects is yet to come although some scientists have pointed out towards the role of the noble metal type in the catalytic activity for the reduction of the oxidant.
2. Etching rate can be improved by_____
a) lowering the temperature
b) using less active oxidant and highly active etchant
c) increasing the number of electronic holes
d) reducing the surface area of the pores so that less time will be required for the etching
Answer: c
Explanation: The more the injected electronic holes the faster the etching rate, resulting in a more efficient diffusion of electronic holes towards the side walls during the etching process and enabling the formation of μpSi structures on the side walls of pores or wires.
3. Noble metals affect the etching rate but not the geometric features of the resulting pSi.
a) True
b) False
Answer: b
Explanation: The geometric features and morphology of the resulting pSi structures are mainly established by the shape of the noble metal deposited on the surface of the silicon wafer as a result of its catalytic effect, which results in a much faster etching rate at the interface noble metal-silicon.
4. Wire-like pSi structures are produced when the distance between noble metal particles is reduced.
a) True
b) False
Answer: a
Explanation: Usually, well-defined and separated pores are produced from single particles distributed across the silicon surface. In contrast, when the distance between adjacent particles is reduced, wire-like or wall-like pSi structures are produced.
5. Pores produced by metal assisted etching feature _____ structure.
a) square-like
b) cylindrical
c) cone-like
d) needle-like
Answer: c
Explanation: Typically, pores produced by metal assisted etching feature a cone-like structure with pore diameter decreasing with depth. This conical effect can be more or less pronounced, depending on the etching conditions.
6. The pore diameter at the pore mouth is always equal to that of the initial noble metal particle.
a) True
b) False
Answer: a
Explanation: The conical effect in the pores formed by metal-assisted approach can be more or less pronounced, depending on the etching conditions, and the pore diameter at the pore mouth can be bigger or smaller than that of the initial noble metal particle.
7. The diameter of the pores can be said to be dependant on the diffusion of electronic holes injected from the noble metal-silicon interface.
a) True
b) False
Answer: a
Explanation: The conical effect can be associated with the diffusion of electronic holes injected from the noble metal-silicon interface to the side walls, the partial dissolution of silicon by the etchant and the progressive dissolution and re-deposition of noble metal in the course of the etching process.
8. _____ is/are obtained when a homogeneous noble metal film is deposited on the surface of silicon.
a) Conical structure
b) Distorted and rough surfaces
c) Honey-comb structure
d) Wire-like structure
Answer: d
Explanation: Silicon wires with well-defined geometry and shape are obtained when a homogeneous noble metal film featuring holes is deposited on the surface of a silicon substrate and subsequently etched in a suitable etchant solution.
9. Lithographic approach along with noble metal is used to produce highly ordered pores.
a) True
b) False
Answer: a
Explanation: Silicon wires can be produced with highly ordered distribution and precisely controlled geometry if the surface of the silicon is patterned by lithographic approaches prior to the deposition of the noble metal film.
10. The morphology of the resulting pSi structures is dependent on the noble metal film.
a) True
b) False
Answer: a
Explanation: The thickness of the noble metal film has a direct effect on the morphology of the resulting pSi structures as well. For instance, 3 and 5 nm thick films of gold lead to pores and wires, respectively. In the case of silver films, 5 nm thick films yield pores while films of 20–50 nm thickness result in silicon wires.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 16”.
1. The configuration of the noble metal film is dependent on the deposition method used.
a) True
b) False
Answer: a
Explanation: It is important to bear in mind that the morphology of the resulting noble metal films can vary with the deposition technique and the nature of the noble metal.
2. The stability of the noble metal in the etchant is dependent on its nature.
a) True
b) False
Answer: a
Explanation: Regarding the stability of the noble metal in the etchant, this is highly dependent on its nature and some noble metals can be oxidised and dissolved in the course of the etching process according to the existing relationship between the electrochemical potentials of the noble metal and the oxidant.
3. Which of the following particles, leads to pores or wires with heterogeneous geometric features?
a) Ag
b) Au
c) Cu
d) Cr
Answer: a
Explanation: Ag particles dissolve and re-deposit during the etching process as a result of the relatively low electrochemical potential of silver. Therefore, Ag particles can change their shape and morphology during this process, leading to pores or wires with heterogeneous geometric features and morphologies with depth.
4. Which of the following particles are used to produce pSi structures with well-defined geometric features?
a) Zn
b) Cd
c) Pd
d) Au
Answer: d
Explanation: Usually, Au particles and films are preferably used to produce pSi structures with well-defined and precisely controlled geometric features and morphologies due to its stability in the etchant. For instance, Au meshes have been used to fabricate silicon wires of high aspect ratio .
5. Illumination of light in metal-assisted etching of silicon affects the etching rate.
a) True
b) False
Answer: a
Explanation: As far as the effect of light illumination in metal-assisted etching of silicon, this has a direct effect on the etching rate. It has been reported that the etching rates for p-type and n-type silicon substrates of resistivity 1–10 Ω cm differ whether the etching process is conducted with or without illumination.
6. The etching rate of silicon wafers under light illumination is much slower than under dark conditions.
a) True
b) False
Answer: b
Explanation: The etching rate of p- and n-type silicon wafers under room light illumination is about 0.05 times faster than under dark conditions. This difference becomes even higher when 20 W illumination is used.
7. The faster etch rates of the silicon wafer under light illumination is due to photo-excited electronic holes.
a) True
b) False
Answer: a
Explanation: The etching rate of p- and n-type silicon wafers under room light illumination is about 0.05 times faster than under dark conditions. This effect can be explained by the fact that under illumination the number of photo-excited electronic holes can be higher than the number of electronic holes injected from the oxidant agent, thus enabling faster etching rates.
8. Metal assisted etching of silicon is dependent on the orientation of silicon atoms in the structure.
a) True
b) False
Answer: a
Explanation: Actually, metal assisted etching of silicon is anisotropic and dependent on the crystallographic orientation of silicon. As an example, slanted porous silicon structures can be produced by etching and silicon wafers.
9. The etching of silicon atoms becomes more difficult for stronger back-bonds.
a) True
b) False
Answer: a
Explanation: The back-bonds of the silicon atoms located on the surface of the substrate must be broken during the oxidation and dissolution of silicon. Therefore, the etching of silicon atoms becomes more difficult for stronger back-bonds. In that respect, it is worth noting that silicon atoms have one, two and three back-bonds in , and substrates.
10. Intrinsic properties of silicon substrate have no effect in the metal assisted etching of Si.
a) True
b) False
Answer: b
Explanation: The Important parameter affecting the resulting pSi structures produced by metal-assisted etching are the different intrinsic properties of the silicon substrate, which have a direct effect on the geometric features and characteristics of the resulting pSi structures.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 17”.
1. The etching rate in p-type silicon is faster than that of n-type silicon.
a) True
b) False
Answer: a
Explanation: As far as the doping type is concerned, the etching rate in n-type silicon is faster than that of p-type silicon for and crystallographic orientations with the same resistivity .
2. The morphology of silicon nanowires produced by metal-assisted etching of silicon changes with the doping level.
a) True
b) False
Answer: a
Explanation: The etching rate is not the only parameter affected by the type of doping. It has been reported that the morphology of silicon nanowires produced by metal-assisted etching of silicon changes with the doping level of the wafer as well and they can present rough surface or contain mpSi or μpSi structures on the side walls with increasing doping level.
3. In highly doped silicon wafers the diffusion of electronic holes occurs from _____
a) noble-metal to silicon
b) noble-metal silicon interface to bulk silicon
c) silicon to noble-metal
d) there is no electron hole transfer
Answer: b
Explanation: In highly doped silicon wafers the diffusion of electronic holes occurs from the
interface noble metal-silicon to the bulk silicon substrate, which would result in the etching of the side walls, producing mpSi or μpSi structures.
4. Lithographic techniques can produce silicon wafers with well-defined geometric features.
a) True
b) False
Answer: a
Explanation: Porous Si structures with precisely controlled and exquisitely defined morphology and geometric features can be produced when the surface of the silicon wafer is patterned by lithographic techniques prior to the etching step.
5. Among all the lithographic techniques, interference lithography, nano-spheres lithography give better results.
a) True
b) False
Answer: a
Explanation: Some lithographic methods have demonstrated outstanding results when combined with metal-assisted etching. The most representative ones are interference lithography, nano-porous anodic alumina masks and nano-spheres lithography.
6. IL provides excellent definition of features at nanometric scale.
a) True
b) False
Answer: a
Explanation: Interference lithography is a top-down nanofabrication technique with high throughput and scalability for large surface areas used in the production of nanostructures. IL provides excellent definition of features at nanometric scale. Usually, an IL pattern is generated by two coherent laser beams and subsequently transferred to a film of photoresist covering the substrate.
7. IL can be combined with metal-assisted etching to produce _____ Choose the correct one.
a) silicon bars
b) porous silicon
c) porous silicon sheets
d) silicon nanowires
Answer: d
Explanation: IL can be combined with metal-assisted etching to produce silicon nanowires. Scientists used this approach to produce silicon nanowires by metal-assisted etching. In this study, first, silicon substrates were coated by a layer of photoresist, which was cured and exposed to IL. This process resulted in perfectly ordered arrays of silicon nanowires.
8. Silicon wires with square and rectangular can be produced by IL technique.
a) True
b) False
Answer: a
Explanation: The geometric features and arrangement of these arrays of silicon wires can be accurately designed by modifying the IL patterns and the feature size and its shape. Therefore, silicon wires with square, rectangular and circular cross-sections can be produced by this approach.
9. To etch the surface of silicon wafers at specific positions by metal-assisted etching, nano-porous anodic alumina mask technique is used.
a) True
b) False
Answer: a
Explanation: Another approach used to etch the surface of silicon wafers at specific positions by metal-assisted etching is the use of nanoporous anodic alumina masks. Self-ordered NAA is basically a nanoporous matrix based on alumina (aluminium oxide–Al 2 O 3 ) that features close-packed arrays of hexagonally arranged cells, at the centre of which a cylindrical nanopore grows perpendicularly to the underlying aluminium substrate.
10. NAA is produced by electrochemical anodization of _____
a) silicon
b) aluminium
c) noble-metals
d) carbon
Answer: b
Explanation: NAA is produced by electrochemical anodization of aluminium, which is typically performed in acid electrolytes based on aqueous solutions of sulphuric (H 2 SO 4 ), oxalic (H 2 C 2 O 4 ) or phosphoric acids (H 3 PO 4 ).
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electrochemical Etching – 18”.
1. In interference lithography technique, aluminium is used as anode.
a) True
b) False
Answer: a
Explanation: In this system and similar to electrochemical etching of silicon, the anode and cathode are immersed in the acid electrolyte.
2. In IL technique, nanopores are produced by application of current and voltage.
a) True
b) False
Answer: a
Explanation: The growth of nanopores is produced by the application of current or voltage. Note that the geometric features of pores in NAA can be precisely controlled by the anodization parameters.
3. Pore sizes in NAA can range from ____
a) 10—100 nm
b) 20—250 nm
c) 20—400 nm
d) 100—550 nm
Answer: c
Explanation: Typically, pore sizes in nanoporous anodic alumina technique can range from 20 to 400 nm, with a pore density from 5 × 108 to 3 × 1010 pores per cm 2 .
4. The NAA technique can produce silicon nano wires with high crystalline quality.
a) True
b) False
Answer: a
Explanation: This lithographic approach makes it possible to produce silicon wires with controlled geometry, morphology and size with high crystalline quality and smooth surface.
5. The geometric features of the resulting silicon nanowires are independent of the noble-metal thickness.
a) True
b) False
Answer: a
Explanation: The geometric and morphological features of the resulting silicon nanowires are dependent on the thickness of the noble metal film.
6. The pores produced by RIE etching can have a thin defective region.
a) True
b) False
Answer: a
Explanation: The pores produced by RIE etching can have a thin defective region, which can prevent or hinder the metal-assisted etching process. To overcome this drawback, the same authors used a slight modification of the traditional NAA approach in order to avoid the use of RIE etching.
7. In the aforementioned approach , which of the following metals is used?
a) V
b) Cr
c) Pt
d) Ag
Answer: a
Explanation: In this new approach, a film of Ag is deposited on the NAA mask and the whole system etched. In this way, the Ag film with holes was transferred from the top of the NAA mask to the surface of the silicon substrate as a result of the dissolution of the NAA mask. Then, the etching occurred on the surface of the silicon by metal-assisted etching catalysed by the Ag film.
8. The use of NAA mask technique to produce pSi structures need simple wet chemistry laboratory.
a) True
b) False
Answer: a
Explanation: The main advantage of the use of NAA masks to produce pSi structures by metal-assisted etching is that it can be carried out in a simple wet chemistry laboratory without expensive facilities.
9. Self-ordered NAA structures do not present any defects and domains.
a) True
b) False
Answer: a
Explanation: Self-ordered NAA structures present defects and domains, which are inevitably transferred to the patterned structure on the silicon substrate and thus to the resulting arrays of silicon nanowires.
10. The NAA approach can produce silicon nano-wires of _____ cross-section.
a) triangular
b) circular
c) square
d) needle like
Answer: b
Explanation: Along with the production of self-ordered pores, another limitation of this approach is that only silicon nanowires featuring circular section can be obtained.
11. Nanosphere lithography method is another lithographic approach extensively used to produce pSi structures.
a) True
b) False
Answer: a
Explanation: Nanosphere lithography method is another lithographic approach extensively used to produce pSi structures by metal-assisted etching. Huang et al. developed an approach where a monolayer of self-assembled polystyrene nanospheres was first deposited on the surface of a silicon substrate. After this, the size and distance between adjacent nanospheres were increased by RIE etching and a noble metal film was deposited on the silicon surface by thermal evaporation.
12. At high aspect ratio, silicon nanowires tend to form bundles.
a) True
b) False
Answer: a
Explanation: It is worthwhile mentioning that silicon nanowires of high aspect ratio trend to form bundles or collapse as a result of surface tension forces during the drying process. This drawback can be overcome by supercritical drying approach.
13. Porous silicon can be used as carriers for drug delivery.
a) True
b) False
Answer: a
Explanation: Its biocompatibility and degradability properties have enabled the use of porous silicon structures as micro and nanocarriers for drug delivery. While it’s outstanding optical properties make porous silicon a unique material to develop optical structures suitable for optical sensing.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Micromachining – 1”.
1. Micro machining processes are used to increase selectivity, accuracy, performance, etc. parameters.
a) True
b) False
Answer: a
Explanation: Micro machining processes are used for;
Minimizing energy and materials used in manufacturing Reduction of power budget
Faster devices
Increased selectivity and sensitivity
Improved accuracy and reliability
Cost/ performance advantages
Integration with electronics, simplifying systems.
2. Choose the odd one out.
a) micro-AJM
b) micro-USM
c) micro-AWJM
d) micro-EDM
Answer: d
Explanation: Among all the processes, micro-AJM , micro-USM micro-AWJM use mechanical energy to remove the material; whereas, micro-EDM process uses thermal energy to remove the material.
3. Choose the odd one out.
a) micro-turning
b) micro-milling
c) micro-EBM
d) micro-grinding
Answer: c
Explanation: Micro-turning, micro-milling and micro-grinding are traditional material removal processes; whereas, micro-EBM process is one of the advanced manufacturing processes.
4. Choose the odd one out.
a) Micro-EBM
b) LBM
c) EDM
d) ECMM
Answer: d
Explanation: Micro-EBM, LBM , EDM processes uses thermal energy for removing material and ECMM process uses chemical energy to remove material.
5. Choose the odd one out.
a) EBM
b) ECM
c) EDM
d) LBM
Answer: d
Explanation: Among all the above mentioned processes, electric discharge micromachining , electron beam micromachining and electrochemical machining are used only for electrically conducting materials; whereas, laser beam micromachining process can be used for both conducting and non-conducting materials.
6. Thermal deformation of the workpiece is the major problem in micromachining.
a) True
b) False
Answer: a
Explanation: Following are the major problems faced during micromachining;
•Mechanical deformation
•Thermal deformation
•Surface integrity
•Gap between tool and work piece
•Coordinate shift in tool handling.
7. In abrasive jet machining, material is removed by shear as well as brittle deformation of the material.
a) True
b) False
Answer: a
Explanation: If the KE of the abrasive particle is high enough, then it will remove the material by shear deformation in case of ductile workpiece material and by brittle fracture if workpiece material is brittle.
8. Holes up to _____ deep can be drilled without using AJM process.
a) 10 nm
b) 45 mm
c) 66 μm
d) 100 μm
Answer: c
Explanation: In AJM, holes up to 66 μm deep can be drilled without employing any special techniques. This process is also useful for producing microcavity.
9. Fused ion beam machining process is based on binding energy of atoms in the workpiece material.
a) True
b) False
Answer: a
Explanation: Fused ion beam machining process is nothing but knocking out atoms from the work-piece surface by the kinetic momentum transfer from incident ion to the target atoms. In this process removal of atoms occur when the actual energy transferred exceeds the usual binding energy.
10. In thermal advanced micromachining process, intense heat is produced.
a) True
b) False
Answer: a
Explanation: In this process, localized intense heat is produced which increases temperature of the workpiece in a narrow zone , equal to its melting or vaporization temperature. Which leads to removal of material at micro/nano level in the form of debris .
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Micromachining – 2”.
1. There is no thermal damage to the workpiece in IBM.
a) True
b) False
Answer: a
Explanation: In case of IBM. An ion hits an atom at the top surface of the workpiece and removes the material atom by atom or in the groups of atoms. Therefore, there is no thermal damage to the workpiece in IBM.
2. Thermal micromachining processes can be used to produce reduced hole diameter, lower hole pitch.
a) True
b) False
Answer: a
Explanation: Reduced hole diameter, lower hole pitch and longer head can be manufactured by thermal micromachining processes. These processes are used to manufacture computer hard disc drive heads, inkjet printer heads, sensors, infrared images.
3. Chemical micromachining is used for engraving the metal.
a) True
b) False
Answer: a
Explanation: It is an ancient process being used for engraving the metal for making ornaments and other products. It removes material in a controlled manner by the application of maskant and etchant.
4. It is required to remove material in the form of atoms for finishing of the surface.
a) True
b) False
Answer: a
Explanation: To finish surfaces to nano level, it is required to remove material in the form of atoms or molecules individually or in groups. Most of the nano finishing processes are using abrasive particles either suspended inliquid or held by the viscoelastic material, carbonyl iron particles, or by the magnetorheological fluid as a carrier.
5. Magneto rheological abrasive finishing is a magnetic field assisted process.
a) True
b) False
Answer: a
Explanation: MRF is a deterministic and magnetic field assisted precision finishing process. MRF uses MRP fluid which is invented by Rabinow in late 1940s consist of CIP , abrasive , carrierliquid , additives .
6. MRF is used for finishing of brittle materials.
a) True
b) False
Answer: a
Explanation: MRF has been used for finishing a large variety of brittle material ranging from optical glasses to hard crystals. The major limitation of this process is that Internal and especially complex surfaces can’t be finished.
7. Abrasive flow machining is used for _____
a) de-burring
b) etching
c) drilling
d) cutting
Answer: a
Explanation: AFM was developed by Extude Home Corporation USA in 1960 as a method to deburr, polish and radius difficult to reach surface like intricate geometries and edges by flowing an abrasive laden viscoelastic medium over them.
8. In chemo-mechanical polishing process, material is removed due to abrading.
a) True
b) False
Answer: a
Explanation: CMP uses both chemical and mechanical type for material removal mechanism. Chemical reaction is used to soften material and then mechanically polish off this layer. Mechanical removal takes place due to abrading.
9. CMP is used for flat surfaces only.
a) True
b) False
Answer: a
Explanation: CMP is not deterministic in nature. End point of CMP is difficult to control for a desired thickness. This process is used for only flat surfaces. Basically, CMP is used to polish the silicon wafer.
10. MAF was developed to produce efficiently and economically good quality finish material.
a) True
b) False
Answer: a
Explanation: MAF was developed to produce efficiently and economically good quality finish on the internal and external surface of tubes as well as flat surface made of magnetic or non-magnetic material.
11. Magnetic Float Polishing is a technique based on_____
a) magneto-dynamic behaviour
b) magneto-hydrodynamic behaviour
c) kinematic behaviour
d) viscosity
Answer: b
Explanation: Magnetic Float Polishing is a technique based on the Magnet on hydrodynamic behaviour of the magnetic fluid which in the presence of magnetic field can levitate a non-magnetic float and abrasive particles suspended in it.
12. Ferromagnetic particles are attracted towards the area of a higher magnetic field.
a) True
b) False
Answer: a
Explanation: When the magnetic field is applied the ferromagnetic particles in the ferrofluid are attracted downward to the area of higher magnetic field and upward buoyant force is exerted on all non-magnetic materials to push them to the area of lower magnetic field.
13. MRAFF is the hybrid finishing process of MRF and AFF.
a) True
b) False
Answer: a
Explanation: MRAFF is the hybrid finishing process to take advantage of both the finishing processes MRF & AFF . Any complex geometry can be finished by this process.
14. In magnetic flow polishing process, very small force is applied by the abrasives.
a) True
b) False
Answer: a
Explanation: The forces applied by abrasives are extremely small and controllable. The balls are polished by the abrasive particles mainly due to the action of the magnetic buoyancy force when the spindle rotates.
15. For replication of micro parts moulding is preferred
a) True
b) False
Answer: a
Explanation: Nowadays, focus is on miniaturization through the development of novel production concepts Misplaced & for the processing of non-ceramic materials. The replication of microparts through moulding is one of the preferred routes for micromanufacture because of its mass-production capability and relatively low cost.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 1”.
1. AJMM is widely used for machining of glass and silicon.
a) True
b) False
Answer: a
Explanation: Abrasive Jet Micro Machining is a relatively new approach to the fabrication of microstructures. AJMM is a promising technique to three-dimensional machining of glass and silicon in order to realize economically viable micro-electro-mechanical systems .
2. In AJMM, workpiece is exposed to abrasive action of the particles.
a) True
b) False
Answer: a
Explanation: It employs a mixture of a fluid with abrasive particles. In contrast to direct blasting, the surface is exposed completely to the erosive action of the particle beam. Hence, before processing, the substrate material has to be partially shielded by applying an erosion resistant mask.
3. This method is used for _____
a) making finished surfaces
b) thread finishing
c) making grooves
d) cutting
Answer: c
Explanation: This method is used for making accurate shallow holes or grooves, and, with the use of masks, patterns on target material.
4. Resulting abrasive action is dependent on the impact angle of the jet.
a) True
b) False
Answer: a
Explanation: The resulting erosion of the target material can be controlled using masks and by varying parameters such as impact angle and particle flux density, velocity, and particle properties.
5. AJMM is capable of machining anisotropic patterns.
a) True
b) False
Answer: a
Explanation: In contrast to conventional micro-fabrication methods, such as wet and dry etching, AJMM is capable of machining anisotropic patterns and suspended structures with high erosion rate and relatively low cost.
6. Which of the following is true about AJMM?
a) It is a low cost method
b) It is toxic towards the environment
c) It is hazardous to human health
d) It is not capable of anisotropic machining
Answer: a
Explanation: Advantages of AJM:
low capital and operating costs,
environment-friendly process,
no major health hazards, and
ability to machine anisotropic and suspended structures on the same substrate.
7. AJM applications include drilling, engraving of glass, etc. operations.
a) True
b) False
Answer: a
Explanation: Typical AJM applications include drilling, cutting and engraving of glass, ceramics and some hard materials. It can also be used to etch labels in plastics and metals, deburr, deflash and clean materials after conventional machining.
8. In AJMM, abrasive particles are accelerated in a gas stream.
a) True
b) False
Answer: a
Explanation: Fine micro abrasive particles are accelerated in a gas stream . The particles are directed towards the focus of machining .
9. In AJMM, as the jet fracture off the surface after striking it.
a) True
b) False
Answer: a
Explanation: As the particles impact the surface, they fracture off the surface and create cavities. As the particle impacts the surface, it causes a small fracture, and the gas stream carries both the abrasive particles and the fractured particles away.
10. The choice of abrasive varies with the type of machining.
a) True
b) False
Answer: a
Explanation: The choice of abrasive particles depends on the type of machining operation. The abrasives should have a sharp and irregular shape for better performance.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 2”.
1. Abrasive particles are suspended in the carrier gas.
a) True
b) False
Answer: a
Explanation: Abrasive particles should be fine enough to remain suspended in the carrier gas. It should have excellent flow characteristics so that narrow and fine areas are reachable to them.
2. SiC is used as abrasive for harder materials.
a) True
b) False
Answer: a
Explanation: Following are the materials used as abrasive in AJMM:
1) Al 2 O 3 : For cleaning, cutting and de-burring
2) SiC: Similar applications as Al 2 O 3 but for harder work materials
3) Glass beads: Matte finish
4) Sodium Bicarbonate: Cleaning, cutting and de-burring of soft material.
3. Which of the following is commonly used as a carrier gas in AJMM?
a) O 2
b) He 2
c) N 2
d) H 2
Answer: c
Explanation: In AJMM, commonly used gases are CO 2 , nitrogen, and air. Air is mostly preferred due to universal availability, practically at no cost, and its non-toxic nature.
4. The Carrier gas should spread more after discharge.
a) True
b) False
Answer: b
Explanation: Following are the required properties for the carrier gas:
1) It should be non-toxic
2) It should be cheap
3) It should be easily available.
4) It must not flare excessively when discharged from the nozzle.
5. There should be supersonic air flow velocity in the nozzle.
a) True
b) False
Answer: a
Explanation: The following requirements have to be fulfilled on nozzle design:
1) Pressure-less constant feeding system
2) Supersonic air flow velocity in the nozzle
3) Homogeneous dispersion of abrasive particles over the width of the nozzle
4) Long life time of the nozzle .
6. A decrease in stand-off-distance _____
a) increases machining time
b) increases energy consumption
c) improves surface finish
d) improves accuracy
Answer: d
Explanation: A decrease in stand-off-distance :
1) improves accuracy,
2) decreases kerf width and
3) reduces taper in the machined groove.
7. Material removal rate in AJMM _____
a) increases with SOD
b) can only decrease
c) first increases upto certain value and then decreases
d) first decreases upto certain value and then increases
Answer: c
Explanation: MRR increases only upto a certain value of abrasive flow rate beyond which it starts decreasing. After a certain value of abrasive flow rate, abrasive flow velocity decreases to the extent that it results in reduction in MRR.
8. MRR increases with abrasive flow rate increase.
a) True
b) False
Answer: a
Explanation: As abrasive flow rate increases, then the number of abrasive particles cutting the material also increases there by increasing Material removal rate .
9. In the case of ductile materials, material is removed by plastic deformation.
a) True
b) False
Answer: a
Explanation: When ductile materials are machined by AJMM, the material is removed by plastic deformation and cutting wear, or plastic strain and deformation wear.
10. In case of ductile materials, plastic deformation starts when yield strength is exceeded.
a) True
b) False
Answer: a
Explanation: In case of ductile materials, during an impact of the jet, plastic deformation takes place in the vicinity of the impact when the yield strength of the material is locally exceeded. And yield strength increases due to hardening of the material.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 3”.
1. In AJMM, material removal starts when the fracture strength is reached.
a) True
b) False
Answer: a
Explanation: During AJMM, plastically deformed surface layer is formed near the eroded surface, and therefore, the yield strength of the material increases. Upon further deformation, the yield strength at the surface of the material will eventually become equal to its fracture strength. The surface becomes brittle and its fragments may be removed by subsequent impacts.
2. Brittle fracture can occur due to indentation rupture.
a) True
b) False
Answer: a
Explanation: Brittle fracture may take place due to:
1) Indentation ruptures
2) Elastic–plastic deformation
3) Critical plastic strain theory
4) Radial cracking and propagation or surface energy criterion.
3. The mass loss of workpiece is proportional to_____
a) power supplied
b) nozzle diameter
c) amount of abrasive
d) carrier gas
Answer: c
Explanation: The mass loss of workpiece is proportional to the amount of abrasive.
Mass loss = (Kρmv 2 )/, where, K is a dimensionless factor, m and v amount and velocity of
particles, and ρ and H are density and hardness of the eroded material, respectively. The above relation is true for brittle erosion but not for softer materials due to time variant erosion behaviour.
4. In AJMM, there is initial weight gain in the workpiece.
a) True
b) False
Answer: a
Explanation: Especially at normal impact angle, particles tend to embed in the material, resulting in an initial gain in weight of the specimen. After this incubation time steady-state erosion is established and mass loss from the eroded material is proportional to the amount of abrasive particles.
5. Erosion rate is directly proportional to velocity of the jet.
a) True
b) False
Answer: a
Explanation: The principal empirical relation between erosion rate Erate, expressed as the quotient of mass loss and amount of abrasive, and particle velocity is given as a power function by
E rate α v k , where k= velocity coefficient.
6. For metal, velocity coefficient ranges from_____
a) 0.5—1
b) 1.8—3
c) 2.3—3
d) 2—4
Answer: c
Explanation: velocity coefficient k commonly reported for,
1) for metals – between 2.3 and 3,
2) for glasses – between 2 and 4 and
3) for elastomers – between 1.8 and 3.2.
7. AJMM can also machine poly methyl methacrylate .
a) True
b) False
Answer: a
Explanation: AJMM can machine much steeper side walls and flatter bottom section in PMMA than those in glass. For PMMA, there is only a small probability of a particle rebounding from the steep side wall and hitting the opposite side.
8. There is appearance of the dimples during AJM.
a) True
b) False
Answer: a
Explanation: Appearance of the dimples during AJM for 10s. for various machining sets of abrasives and ceramic materials. Properties of the dimples do not differ in terms of the removed volume, but also the roughness of the struck face for different combination of abrasive particles and workpiece material.
9. In AJMM, the substrate has to be shielded by a mask.
a) True
b) False
Answer: a
Explanation: In AJMM, the substrate has to be shielded by a wear resistant mask that is patterned with the desired contour. The mask determines the accuracy of the dimensions in the plane of the desired structure.
10. During blasting, the workpiece is exposed to an abrasive air jet pressure of _____ MPa.
a) 0—1
b) 0—0.2
c) 0.2—0.8
d) >1
Answer: c
Explanation: During blasting, the workpiece is exposed to an abrasive air jet pressure of 0.2-0.8 MPa and abrasive particles average diameter of 10-100 μm. The scan strategy and the particle beam profile of the nozzle are of great importance.
This set of Manufacturing Processes online test focuses on “Abrasive Jet Micromachining – 4”.
1. Performance of the AJMM process is dependent on the quality of the mask.
a) True
b) False
Answer: a
Explanation: The quality of the mask influences the performance of AJMM. The main qualification for a good mask material is a low erosion rate. It also requires the capability of an accurate and easy pattern transfer, and the ability to retain the irresistance in discontinuous layers.
2. How many types of materials can be used during AJMM?
a) 1
b) 3
c) 8
d) there is no compulsion on the material
Answer: b
Explanation: Three groups of mask materials can be applied to AJMM:
• Ductile materials such as metals.
• Elastic materials such as elastomer sand.
• Photo-resists as used in IC-industry.
3. The usability of the mask is affected by imaging accuracy.
a) True
b) False
Answer: a
Explanation: Each material used for making mask, needs a sufficient erosion resistance related to the substrate especially at normal blast angles. Furthermore, the achievable imaging accuracy determines the usability of a mask and minimum achievable features size.
4. Which of the following have a low erosion rate?
a) Ductile materials
b) Malleable materials
c) Hardened materials
d) Low melting point materials
Answer: a
Explanation: Ductile materials, like metals, have a low erosion rate, especially at perpendicular impact. This makes them suitable to be used as a mask material. It can be used by means of a thin plate .
5. To apply metal mask plate for AJMM, magnetic clamps are used.
a) True
b) False
Answer: a
Explanation: Metals having low erosion rates are suitable for making masks for AJMM. To apply metal mask plate for AJMM, it can be magnetically clamped directly to the target or by introducing an intermediate protection/ adhesion layer.
6. Limitations in feature size are the major drawback of the metal masks.
a) True
b) False
Answer: a
Explanation: The disadvantages of this mask type are the limitations in feature size and pattern constraints .
7. In AJMM, metals masks can be applied to the workpiece by electroplating.
a) True
b) False
Answer: a
Explanation: In order to combine the low erosion rate of a metal, and the high resolution of a lithographic process, a metal mask can be applied to the target by electroplating. Copper is used by this method, while Zinc mask can be made by electro-forming.
8. The erosion mechanism of rubber-like materials is same as that of brittle materials and ductile materials.
a) True
b) False
Answer: b
Explanation: The erosion mechanism of rubber-like materials differs essentially from that of brittle materials or ductile materials. No lateral cracks are formed in elastomers as found in brittle materials. Neither do any evidence of cutting or ploughing wear as found in metals.
9. Erosion mechanism in elastomer materials is based on fatigue.
a) True
b) False
Answer: a
Explanation: The erosion mechanism of this class of materials is based on fatigue; therefore they display a good erosion resistance. The photosensitive materials can be patterned accurately using lithography. Photosensitive-elastomer can be a good option.
10. Behaviour of elastomer materials is dependent on temperature.
a) True
b) False
Answer: a
Explanation: In contrast to ductile or brittle materials, elastomers behaviour is dependent on temperature, rate of deformation and particle velocity. Thus elastomers can show ductile, elastic and brittle behaviour.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 5”.
1. Elastomer masks are provided in the form of foils.
a) True
b) False
Answer: a
Explanation: These types of mask usually provided in the form of ready-made foil with self-adhesive properties. Besides, elastomers can show ductile, elastic and brittle behaviour and experiments have to be carried out under relevant practical conditions.
2. Photo-resists are _____ materials.
a) photogenic
b) photosensitive
c) photo-dissociate
d) photo-emissive
Answer: b
Explanation: Photo-resists are photo-sensitive materials. There are two types of photo-resists; positive and negative. The major drawback is that it needs Expensive equipment to prepare the mask.
3. Positive resists are formed when resist is exposed to UV light.
a) True
b) False
Answer: a
Explanation: For positive resists, the resist is exposed with UV light wherever the underlying material is to be removed. In these resists, exposure to the UV light changes the chemical structure of the resist so that it becomes more soluble in the developer.
4. After treatment with UV light, resist is washed away by the developer solution.
a) True
b) False
Answer: a
Explanation: The exposed resist, after UV treatment is washed away by the developer solution, leaving windows of the bare underlying material. In other words, “whatever shows, goes.” The mask, therefore, contains an exact copy of the pattern which is to remain on the wafer.
5. SU-8 is most commonly used negative resist.
a) True
b) False
Answer: a
Explanation: Negative resists behave in just the opposite manner as that of the positive resists. Epoxy-based SU-8 is one of the good negative resists. It is able to provide features with high aspect ratios with UV-lithography.
6. Structures with high aspect ratios are possible with _____
a) photo-resist material
b) metals
c) elastomers
d) porous silicon
Answer: b
Explanation: Stainless steel masks are very suitable for high particle velocities and fast machining operations. Structures with high aspect ratios are achievable due to the low erosion rate of steel. Attention has been paid to the adhesive layer, which should not only stick the two materials together but also avoid under etching.
7. Feature width is the major drawback of metal masks.
a) True
b) False
Answer: a
Explanation: The limiting factors for all metal masks are the feature width and the structuring procedure where no free-standing contours are possible. Metal masks should be applied preferably for medium and large sizes.
8. Elastomers are suitable for high air pressures.
a) True
b) False
Answer: a
Explanation: Elastomer foils are easy to pattern and allow a high complexity of the design but the procedure is somewhat time consuming. They are not suitable for high air pressures due to their elastic deformation behaviour.
9. At higher particle velocities, adhesion between the mask and the workpiece material becomes weak.
a) True
b) False
Answer: a
Explanation: The adhesion is significantly weaker for complex patterns and higher particle velocities that may cause a release of the foils from the substrate. Their applicability is limited to single workpieces and feature sizes down to 75μm.
10. High aspect ratios are not possible with SU-8 material.
a) True
b) False
Answer: a
Explanation: A good compromise in terms of feature size and imaging accuracy gives the epoxy based photo-resist SU-8. Since the maximum thickness of an SU-8 layer is about 300μm, no high aspect ratio is achievable and its application is limited to shallow cavities.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 6”.
1. Powder flowability is affected by particle size and surface texture.
a) True
b) False
Answer: a
Explanation: Powder flowability and compatibility are greatly influenced by particle size, size distribution, moisture content, and surface texture.
2. Adhesion between particles can be increased by moisture.
a) True
b) False
Answer: a
Explanation: Inter particle adhesion is further enhanced by moisture that adsorbs readily onto these hygroscopic surfaces.
3. Relative humidity can affect adhesive forces.
a) True
b) False
Answer: a
Explanation: The relative humidity of stored air can have a major influence on the adhesive forces at the interface of particles. But one of the major difficulties with the AJMM process is the handling of very fine abrasive particles.
4. Movement of powder leads to stratification.
a) True
b) False
Answer: a
Explanation: It is well known that the movement of powder leads quickly to stratification and the creation of gradient of particle size and/ or shape. Such problems result in alteration of the powder mass flow rate during the course of AJMM experiments.
5. Powder feed control of micro-blasting systems is divided into _____
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: The powder feed control of two micro-blasting systems is considered into two types.
• Pressurized powder feed system
• Fluidized bed powder spray system.
6. Vibratory or screw feeding systems are another approach to control the powder mass flow rate.
a) True
b) False
Answer: a
Explanation: Other approaches to the control of powder mass flow rate include vibratory and screw or auger feeding in which the powder is fed to the conveying air through an auger .
7. In powder feeding systems, powder bridging, compaction, and agglomeration are desirable.
a) True
b) False
Answer: b
Explanation: Introducing a vibrator to a screw system improve the steadiness of the powder feed But the improvement diminishes with fine, more cohesive materials such as zeolites and cement powders due to phenomena such as powder bridging, compaction, and agglomeration.
8. In AJMM, the powder is fed _____
a) through air stream
b) through a water pipe
c) along with a gel, which improves the adhesion between particles
d) in the form of batches
Answer: a
Explanation: The powder is fed through the air stream from a pressurized reservoir through an orifice and mixing chamber. The system utilizes an oscillating valve that splits the operation cycle into two halves.
9. The operation cycle is activated when the entire system is pressurized.
a) True
b) False
Answer: a
Explanation: The operation cycle is activated by a switch only after the entire system, including reservoir, has initially been pressurized by closing the nozzle end and opening the oscillating valve to the main air supply.
10. During powder feeding, the oscillating valve is open for the first half of the operation cycle.
a) True
b) False
Answer: a
Explanation: During the first half of the operation cycle, the oscillating valve is open, allowing air to flow from the pressure regulator to the mixing chamber while some enters the powder reservoir and the rest flows out through the opened nozzle.
This set of Manufacturing Processes written test Questions & Answers focuses on “Abrasive Jet Micromachining – 7”.
1. During the first half cycle in pressurized powder feed system, powder that has entered the mixing chamber is _____
a) forced out of the nozzle
b) heated to a specific temperature
c) mixed with air
d) mixed with cutting fluid
Answer: a
Explanation: It is during this first half cycle that any powder that has entered the mixing chamber is forced out of the nozzle. In the second half of the cycle, the oscillating valve is closed, stopping air flow through the system.
2. During first half cycle, mixing chamber is at ___________
a) atmospheric pressure
b) 2 atm
c) 2 bar
d) vacuum
Answer: a
Explanation: During the first half cycle the powder in the chamber is forced out of the nozzle. At this point, the reservoir is still pressurized, but the mixing chamber is at atmospheric pressure due to the open nozzle. This creates a pressure differential that forces the powder down through the orifice at the bottom of the reservoir and into the mixing chamber.
3. Powder mass flow rate is controlled by _____________
a) regulating the air flow rate
b) nozzle diameter
c) size of the mixing chamber
d) cycle time
Answer: a
Explanation: Limited control of the powder mass flow rate is possible by regulating the air flow rate through the reservoir, by changing the orifice bypass, and the size of the reservoir orifice.
4. In fluidized bed powder spray system, the air flow from the bottom of the reservoir creates_____
a) pressure in the system
b) a cloud of powder particles
c) vacuum in the system
d) high turbulence to increase the effectiveness
Answer: b
Explanation: In this system, upward high-speed air flow from the bottom of the reservoir through the powder bed created a cloud of suspended particles. Some of which settled into a collection funnel at the top of the reservoir that is connected to the air stream leading to the nozzle.
5. Which of the following is true about powder flow rate in fluidized bed powder system and other systems?
a) First has higher flow rate the other
b) First has lower flow rate the other
c) There is no relation as it is dependent on nozzle parameters
d) Powder flow rate in is not a measurable parameter
Answer: a
Explanation: Fluidized bed powder spray is operated at significantly higher powder mass flow rate than the pressurized powder feed system. The mass flow rate could be regulated to some extent by changing the diameter of the funnel.
6. The powder mass flow rate is dependent on_____
a) fineness of powder particles
b) type of mask used during the process
c) carrier gas
d) amount of powder
Answer: d
Explanation: The powder mass flow rate is dependent on the amount of powder in the reservoir. The powder mass flow rate obtained by fluidized system decreased rapidly as the powder in the reservoir chamber is consumed.
7. Powder compaction is desirable during AJMM.
a) True
b) False
Answer: b
Explanation: This phenomenon usually happens in the pressurized powder feed system. The powder is firmly compacted during the course of AJMM process. Due to this cavities are formed in the supply line, which is not at all desirable.
8. There are variations in the powder mass flow rate due to_____
a) powder compaction
b) size of the powder particles
c) air flow rate inside the mixing chamber
d) pressure build-up in the chamber
Answer: a
Explanation: Due to powder compaction, cavities often form in the vicinity of the orifice, likely causing variations in the powder mass flow rate as the cavity walls collapse randomly, injecting bursts of powder into the nozzle.
9. Mounting a variable speed rotary electric mixer above the reservoir can reduce powder compaction.
a) True
b) False
Answer: a
Explanation: In order to reduce powder compaction in the reservoir of the pressurized powder feed system, the system can be modified by mounting a variable speed rotary electric mixer above the reservoir with the shaft passing through a pressure-seal bearing that had been mounted into the reservoir cap.
10. The degree of powder stratification is not affected by_____
a) mixing time
b) powder mass flow rate
c) air flow velocity
d) diameter of the funnel in the mixing chamber
Answer: a
Explanation: Powders stratify as they flow and it depends on particle size. Mixing time did not appear to affect the degree of particle stratification significantly.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 8”.
1. The powder distribution changes because of _____
a) powder stratification
b) variation in feed rates
c) variation in nozzle diameter
d) variation in air flow velocity
Answer: a
Explanation: Powders stratify as they flow and it depends on particle size. Therefore, the powder size distribution changes while blasting, as the smaller particles are ejected first, leaving the larger ones to remain in the reservoir.
2. Powder size distribution can be minimised by ___________
a) increasing the carrier gas flow
b) increasing the amount of the powder in the reservoir
c) decreasing the amount of the powder in the reservoir
d) using very fine powder
Answer: c
Explanation: However, in most practical applications, a relatively small amount of powder is used during a single machining operation, and therefore a negligible change in the powder size distribution occurs.
3. Refilling the reservoir is another way to get good results in AJMM.
a) True
b) False
Answer: a
Explanation: The powder size distribution changes while blasting because of powder stratification. Using a relatively small amount of powder during the process can improve powder distribution but to ensure repeatable results, the powder reservoir should be emptied and refilled with fresh powder.
4. Mechanical properties of powder are influenced by _____
a) humidity
b) carrier gas
c) air velocity
d) type of mask used
Answer: a
Explanation: Mechanical properties of powder are influenced by humidity. Increasing humidity decreases the fracture toughness, which can have a large effect on the resulting solid particle erosion rates.
5. Humidity can affect_____
a) machining time required
b) powder flowability
c) metal mask thickness
d) Powder stratification
Answer: b
Explanation: Humidity can also greatly influence the powder flowability and the repeatability of particle mass flow rates since it has a direct effect on inter-particle adhesion.
6. Which of the following is done to minimize the effects due to humidity?
a) Increasing the exposure of the powder to atmospheric air
b) Drying the air before entering the mixing chamber
c) Using photo sensitive mask
d) Using pressurized powder feed system
Answer: b
Explanation: To minimize the effects due to humidity, sacks of desiccant were placed inside the sealed powders to rage bottles, and both a desiccant-based and a refrigeration air dryer are used to dry the compressed air. Achieving a moisture free powder reservoir however, is difficult because of its frequent exposure to atmospheric moisture when it was opened to be refilled.
7. Which of the following is not true about AJMM?
a) It can be used for shallow depth cut on ceramic materials
b) It can be used for medical applications
c) It can be used for pressure sensors
d) It can be used in machining of high strength materials
Answer: a
Explanation: Following are the few applications of AJMM;
• Shallow depth cut on ceramic materials
• Trenches for micro-medical applications
• Mesas to reduce the surface area of chuck and other semiconductor components
• Reference cavities for pressure sensors.
8. AJMM can be used for de-burring and polishing plastic.
a) True
b) False
Answer: a
Explanation: AJMM is used for;
• Thru-holes for air and chemical flow
• Cavities for mechanical locations
• Removing flash and parting lines from injection molded parts
• De-burring and polishing plastic, nylon and Teflon components
• Cleaning metallic mould cavities which otherwise may be inaccessible.
9. _____ can be fabricated by AJMM.
a) Annealed glass
b) Toughened glass
c) Mirrored glass
d) Pyrex glass wafers
Answer: d
Explanation: Cantilever beam in pyrex glass wafers for inertial sensor applications can be fabricated by AJMM. This can be made by erosion process which consists of etching through the complete wafer .
This set of Manufacturing Processes online quiz focuses on “Abrasive Jet Micromachining – 9”.
1. Which of the following technology is used for ferrite substrates?
a) Powder coating
b) Powder blasting
c) Sintering
d) Continuous powder processing
Answer: b
Explanation: Another possible application of the powder blasting technology is the micro-structuring of ferrite substrates. In this case, powder blasting proved to be not only the most appropriate but also a very fast and cheaper way to get such structures.
2. Manufacturing of capillary electrophoresis chips has an application of which of the following process?
a) Ultrasonic machining
b) Chemical Milling
c) Abrasive jet machining
d) Electron beam machining
Answer: c
Explanation: The device consists of a glass chip which contains a single separation channel as well as an integrated conductivity detection cell. In contrast to most micro-fluidic glass devices, the channels are not wet etched in HF but machined by AJMM which allows the creation of micro-structures below 100μm, and additionally makes parallel holes machining at very low costs outside the clean room environment.
3. Monolithic suspended micro-structure in glass was realized using _____
a) oblique AJMM
b) ion beam technique
c) photo chemical technique
d) laser beam technique
Answer: a
Explanation: Complex three-dimensional and monolithic suspended microstructure in glass was realized using normal and oblique AJMM. By controlling the under etching induced by oblique AJMM blasting, millimetrer high microstructure single as scan be fabricated with an aspect ratio of 5:10, as well as free-standing monolithic 100-μm-wide structures, suspended over many millimeters.
4. The mask using SU8, _____ is applied as a micro-pattern for AJMM process.
a) SU6
b) SU7
c) SU8
d) SU9
Answer: c
Explanation: A passive micro-mixer with3-dimensional feature fabricated by AJMM process by employing photo-polymer as a mask on a glass slide target. The mask using SU8, a photo-sensitive polymer is applied as a micro-pattern for AJMM process. The fabrication process involved three glass target slides and conducted multi-masking processes with four different mask patterns.
5. Which of the following is true about AJMM?
a) It is a high maintenance process
b) It is a time consuming process
c) Depths upto few microns are not possible
d) Multiple features can be machined in one operation
Answer: d
Explanation: Following are the few advantages of AJMM;
• Minimal tooling cost
• Quick turn-around for prototyping and development work
• Feature sizes down to 100 μm and featured depths to just a few microns are possible
• Multiple features can be machined in one operation.
6. AJMM generates no heat.
a) True
b) False
Answer: a
Explanation: Following are the few advantages of AJMM;
• The process generates no heat and does not change the material properties of the work-piece
• Very high pattern densities are possible
• Process works well with metalized parts
• Features can be of any 2D shape: square, round, designed shapes, and connected channels.
7. Abrasive jet machined features have tapered sidewalls ranging from _____
a) 5—10˚
b) 22—28˚
c) 15—30˚
d) 18—26˚
Answer: d
Explanation: Unlike vertical side walls produced by ultrasonic machining, abrasive blasting machined features have tapered sidewalls ranging from 18 to 26˚, depending on several factors.
8. Maximum possible aspect ratio in AJMM is_____
a) 1:2
b) 1.5:3
c) 2:1
d) 3:1
Answer: d
Explanation: In AJMM, maximum aspect ratio is 3:1 . Therefore, its applications are restricted to brittle materials because of low MRR in case of ductile materials.
9. Which of the following is correct about AJMM?
a) It requires no cleaning
b) It has very high accuracy
c) It tends to pollute the environment
d) The nozzle has very less wear
Answer: c
Explanation: Following are the limitations of AJMM;
• Sometimes additional cleaning operation is required to machine parts to remove abrasives from the surface
• Machining accuracy is poor
• Nozzle wear rate is high
• The process tends to pollute the environment.
10. Dimensional tolerances of very less microns are possible with AJMM
a) True
b) False
Answer: a
Explanation: With AJMM, feature location and dimensional tolerances down to +/-25 microns are possible. Also, features of any 2D shape: square, round, designed shapes, and connected channels can be machined.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 10”.
1. AJM nozzles are made from which of the following materials?
a) Low carbon steel
b) HSS
c) WC
d) Stainless steel
Answer: c
Explanation: Generally, the nozzle is made of;
• Material – WC / sapphire
• Diameter – 0.2 ~ 0.8 mm
• Life – 10 ~ 300 hours.
2. Material removal in AJM of glass is around_____
a) 0.1 mm 3 /min
b) 15 mm 3 /min
c) 15 mm 3 /s
d) 1500 mm 3 /min
Answer: b
Explanation: Following are the limitations of AJMM;
• MRR is rather low (around ~ 15 mm 3 /min for machining glass)
• Abrasive particles tend to get embedded particularly if the work material is ductile
• Tapering occurs due to flaring of the jet
• Environmental load is rather high.
3. Material removal takes place in AJM due to _____
a) electrochemical action
b) mechanical impact
c) fatigue failure of the material
d) sparking on impact
Answer: b
Explanation: In Abrasive Jet Machining , abrasive particles are made to impinge on the work material at a high velocity. The high velocity abrasive particles remove the material by micro-cutting action as well as brittle fracture of the work material.
4. As the stand-off distance increases, the depth of penetration in AJM _____
a) increases
b) decreases
c) does not change
d) initially increases and then remains steady
Answer: b
Explanation: The depth of penetration varies inversely with the stand-off distance. In AJM, generally, the abrasive particles of around 50 μm grit size would impinge on the work material at a velocity of 200 m/s from a nozzle of I.D. of 0.5 mm with a stand-off distance of around 2 mm.
5. If air is used as a carrier gas, the pressure of the air is maintained at around_____
a) 1 bar
b) 3 bar
c) 5 bar
d) 3.5 bar
Answer: c
Explanation: In AJM, air is compressed in an air compressor and compressed air at a pressure of around 5 bar is used as the carrier gas. Gases like CO 2 , N 2 can also be used as carrier gas which may directly be issued from a gas cylinder. Generally, oxygen is not used as a carrier gas.
6. The mass flow rate of abrasive entering the chamber is independent of the amplitude of vibration of the sieve .
a) True
b) False
Answer: b
Explanation: The abrasive particles enter the chamber from a hopper through a metallic sieve. The sieve is constantly vibrated by an electromagnetic shaker. The mass flow rate of abrasive entering the chamber depends on the amplitude of vibration of the sieve and its frequency. The abrasive particles are then carried by the carrier gas to the machining chamber via an electro-magnetic on-off valve.
7. In AJMM, impingement angle is kept approximately in range of_____
a) 10 0 ~ 20 0
b) 30 0 ~ 45 0
c) 60 0 ~ 90 0
d) 50 0 ~ 60 0
Answer: c
Explanation: Generally, abrasive jet has,
• Velocity : 10 0 ~ 30 0 m/s
• Mixing ratio : mass flow ratio of abrasive to gas = mass of abrasive/ mass of carrier gas
• Stand-off distance : 0.5 ~ 5 mm
• Impingement Angle : 60 0 ~ 90 0 .
8. Which of the following is used as abrasive in AJMM?
a) Al 2 O 3
b) HNO 3
c) FeC
d) CaCO 3
Answer: a
Explanation: Abrasive used in AJMM is:
• Material – Al 2 O 3 / SiC / glass beads
• Shape – irregular / spherical
• Size – 10 ~ 50 μm
• Mass flow rate – 2 ~ 20 gm/min.
9. Which of the following assumption is true about AJMM?
a) Abrasives are irregular in shape.
b) The abrasive particles are characterised by the mean grit diameter
c) Brittle materials are considered to fail due to fatigue
d) The kinetic energy of the abrasives is partially lost in overcoming the friction in the nozzle
Answer: b
Explanation: Modelling in AJMM is done with the following assumptions:
Abrasives are spherical in shape and rigid. The particles are characterised by the mean grit diameter
The kinetic energy of the abrasives are fully utilized in removing material
Brittle materials are considered to fail due to brittle fracture and the fracture volume is considered to be hemispherical with diameter equal to chordal length of the indentation
For ductile material, removal volume is assumed to be equal to the indentation volume due to particulate impact.
10. By AJMM, holes of intricate shapes can be drilled easily.
a) True
b) False
Answer: a
Explanation: Following are the advantages of AJMM process;
• For drilling holes of intricate shapes in hard and brittle materials
• For machining fragile, brittle and heat sensitive materials
• AJM can be used for drilling, cutting, de-burring, cleaning and etching.
• Micro-machining of brittle materials.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 11”.
1. Water Jet Machining and Abrasive Jet Micromachining can be achieved using how many different approaches?
a) 10
b) 5
c) 7
d) only one approach is there
Answer: c
Explanation: WJM and AWJM can be achieved using different approaches and methodologies as enumerated below:
WJM – Pure
WJM – with stabilizer
AWJM – entrained – three phase – abrasive, water and air
AWJM – suspended – two phase – abrasive and water
Direct pumping
Indirect pumping
Bypass pumping.
2. In AJMM, water at _____ MPa is pumped.
a) 100-150
b) 200-400
c) 200-300
d) 370-500
Answer: b
Explanation: Water is pumped at sufficiently high pressure, 200-400 MPa using intensifier technology. An intensifier works on the simple principle of pressure amplification using hydraulic cylinders of different cross-sections as used in jute bell presses.
3. In pure WJM, commercially pure water is used.
a) True
b) False
Answer: a
Explanation: In pure WJM, commercially pure water is used for machining purpose. However as the high velocity water jet is discharged from the orifice, the jet tends to get dispersed in the atmosphere.
4. To stop the dispersion of the water jet in the atmosphere ______ is used.
a) sodium Carboxylate
b) acrylonitrile
c) long chain polymers
d) silica gel
Answer: c
Explanation: However as the high velocity water jet is discharged from the orifice, the jet tends to entrain atmospheric air and flares out decreasing its cutting ability. Hence, quite often stabilisers that hinder the fragmentation of water jet are added to the water.
5. In entrained type AWJM, abrasive water jet has a velocity of around _____ m/s.
a) 100
b) 220
c) 650
d) 800
Answer: d
Explanation: In entrained type AWJM, the abrasive particles are allowed to entrain in water jet to form abrasive water jet with a significant velocity of 800 m/s. Such high velocity abrasive jet can machine almost any material.
6. Which of the following materials, is not machined using abrasive water jet machining?
a) Diamond
b) Concrete
c) Stone – Granite
d) Reinforced plastics
Answer: a
Explanation: The materials which are generally machined using abrasive water jet machining, are given below:
Steels
Non-ferrous alloys
Ti alloys, Ni- alloys
Polymers
Honeycombs
Metal Matrix Composite
Ceramic Matrix Composite
Concrete
Stone – Granite
Wood
Reinforced plastics
Metal Polymer Laminates
Glass Fibre Metal Laminates.
7. For which of the following operations, abrasive water jet machining is not used?
a) Peening
b) Pocket milling
c) Mass immunization
d) Cutting hard materials
Answer: d
Explanation: The abrasive water jet machining can be used for:
Paint removal
Cleaning
Cutting soft materials
Cutting frozen meat
Textile, Leather industry
Mass Immunization
Surgery
Peening
Cutting
Pocket Milling
Drilling
Turning
Nuclear Plant Dismantling.
8. Assuming no losses, what will be the water jet velocity, when the water pressure is 4000 bar, being issued from an orifice of diameter 0.3 mm?
a) 212 m/s
b) 467 m/s
c) 592 m/s
d) 894 m/s
Answer: d
Explanation: manufacturing-processes-questions-answers-abrasive-jet-micromachining-11-q8
9. What will be the mass flow rate of water, when the water pressure is 4000 bar, being issued from an orifice of diameter 0.3 mm, assuming all related coefficients to be 1?
a) 1 kg/min
b) 2.89 kg/min
c) 3.26 kg/min
d) 3.79 kg/min
Answer: d
Explanation: Mass flow rate of water, m w = ρ*Q where, ρ = density of water and Q = discharge of the jet.
m w = ρ*Q
= ρ*(π*d 2 /4)*v
= 1000*3.14*0.0003 2 *894
= 3.79 kg/min
Where, d= diameter of the orifice.
10. Addition of hard and sharp abrasive particles into the water jet can increase the cutting ability of the jet.
a) True
b) False
Answer: a
Explanation: The cutting ability of water jet machining can be improved drastically by adding hard and sharp abrasive particles into the water jet. Thus, WJM is typically used to cut so called softer materials and AWJM is used for relatively harder materials.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 12”.
1. For which of the following applications, simple water jet machining is not used?
a) Textiles
b) Polymers
c) Reinforced plastics
d) Nonferrous metallic alloys
Answer: c
Explanation: WJM is typically used to cut easy-to-machine materials like thin sheets and foils, non-ferrous metallic alloys, wood, textiles, honeycomb, polymers, frozen meat, leather etc.
2. For which of the following applications can be machined by processes other than abrasive water jet machining?
a) Ceramic
b) Steel
c) Metal composites
d) Wood
Answer: d
Explanation: The domain of “harder and “difficult-to-machine” materials like thick plates of steels, aluminium and other commercial materials, metal matrix and ceramic matrix composites, reinforced plastics, layered composites etc., are reserved for AWJM. Soft materials like wood can be machined by simple water jet machining. This saves unnecessary cost incurred in the manufacturing.
3. A standard abrasive water jet machining system contains mixer, accumulator, catcher, etc., modules.
a) True
b) False
Answer: a
Explanation: Any standard abrasive water jet machining system using entrained AWJM methodology consists of following modules:
• LP booster pump
• Hydraulic unit
• Additive Mixer
• Intensifier
• Accumulator
• Flexible high pressure transmission line
• On-off valve
• Orifice
• Mixing Chamber
• Focussing tube or inserts
• Catcher
• CNC table
• Abrasive metering device
• Catcher.
4. A booster pump increases the pressure of the water to _____ bars before supplying it to the next system.
a) 2
b) 5
c) 7
d) 11
Answer: d
Explanation: The water may be directly supplied to the small cylinder of the intensifier or it may be supplied through a booster pump, which typically raises the water pressure to 11 bars before supplying it to the intensifier. Sometimes water is softened or long chain polymers are added in additive unit.
5. To counter drops in delivery pressure, _____ to the delivery unit.
a) a thick cylinder is added
b) an opening is provided
c) an air tight seal is added whose thickness varies corresponding to the pressure changes
d) a flexible joint is added
Answer: a
Explanation: As the intensifier works, it delivers high pressure water. Therefore, as the larger piston changes direction within the intensifier, there would be a drop in the delivery pressure. To counter such drops, a thick cylinder is added to the delivery unit.
6. Accumulator is added because of _____
a) leakages in the system
b) pressure drops is the system
c) operating temperatures
d) safety regulations
Answer: b
Explanation: The change in the direction of the piston causes pressure drop in the delivery line. To counter such drops, a thick cylinder is added to the delivery unit to accommodate water at high pressure. This is called an accumulator which acts like a “fly wheel” of an engine and minimises fluctuation of water pressure.
7. Which of the following is not a part of the cutting head?
a) Orifice
b) Mixing chamber
c) Focussing tube
d) Accumulator
Answer: d
Explanation: High-pressure water from the intensifier is then fed through the flexible stainless steel pipes to the cutting head. Cutting head consists of an orifice, mixing chamber and focussing tube or insert where water jet is formed and mixed with abrasive particles to form abrasive water jet.
8. Generally, the flexible pipe used to carry high pressure water to the cutting head has the diameter equal to _____
a) 4 mm
b) 6 mm
c) 10 mm
d) 12 mm
Answer: b
Explanation: Typical diameter of the flexible stainless steel pipes is of 6 mm. Water carried through the pipes is brought to the jet former or cutting head. Point to be noted here, is that such pipes are to carry water at 4000 bar with flexibility incorporated in them with joints but without any leakage.
9. The orifice is made of _____
a) iron
b) zinc
c) sapphire
d) graphite
Answer: c
Explanation: The orifices are typically made of sapphire. In commercial machines, the life of the sapphire orifice is typically around 100 – 150 hours.
10. Vibratory feeder or toothed belt feeder as used to measure the quantity of the abrasive particles before mixing.
a) True
b) False
Answer: a
Explanation: Metered abrasive particles are introduced into the mixing chamber through a port. The abrasive particles are metered using different techniques like a vibratory feeder or toothed belt feeder. The reader may consult standard literature on transportation of powders.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Abrasive Jet Micromachining – 13”.
1. In AWJM, mixing process takes place in _____
a) intensifier
b) mixing table
c) mixing chamber
d) mixing line
Answer: c
Explanation: Mixing means gradual entrainment of abrasive particles within the water jet. This is done in the mixing chamber. Finally, the abrasive water jet comes out of the focussing tube or the nozzle.
2. Abrasive water jet velocity increases with _____
a) increasing traverse velocity of the job
b) decreasing mass flow rate of abrasive
c) decreasing traverse velocity of the job
d) increasing mass flow rate of abrasive
Answer: d
Explanation: Assuming no losses, abrasive water jet velocity for a given pressure is calculated by formula; manufacturing-processes-questions-answers-abrasive-jet-micromachining-13-q2 where p= pressure. Now mass flow rate is calculated by formula; m w = ρ*A*V w , where A= area of cross section of the jet.
3. In an environment friendly development concerning AWJM, which of the following is used as abrasive?
a) dry ice
b) cubic boron nitrite
c) diamond
d) tungsten carbide
Answer: a
Explanation: In this case, liquid nitrogen replaces the water phase and dry ice crystals (solid CO 2 crystals) replace the abrasive phase leading to no need of disposal or waste generation. The removed work material in the form of microchips can be collected much easily reducing the chances of environmental degradation.
4. The mixing chamber is immediately followed by _____
a) intensifier
b) on-off valve
c) catcher
d) focussing tube
Answer: d
Explanation: The mixing chamber is immediately followed by the focussing tube or the inserts. The focussing tube is generally made of carbide materials.
5. Which of the following materials is used for focusing tubes?
a) Chromium
b) Titanium
c) Nickel
d) Tungsten
Answer: d
Explanation: The focussing tube is generally made of tungsten carbide having an inner diameter of 0.8 to 1.6 mm and a length of 50 to 80 mm.
6. Tungsten carbide is used because of its abrasive resistance.
a) True
b) False
Answer: a
Explanation: Tungsten carbide is used for its abrasive resistance. Abrasive particles during mixing try to enter the jet, but they have reflected away due to an interplay of buoyancy and drag force. They go on interacting with the jet and the inner walls of the mixing tube until they are accelerated using the momentum of the water jet.
7. The formula for abrasive jet velocity considering the momentum loss is _____
a) V awj = η*)*V wj
b) V awj = η**V wj
c) V awj = R*)*V wj
d) V awj = η**V wj
Answer: a
Explanation: As during mixing process momentum loss occurs as the abrasives collide with the water jet and at the inner wall of the focussing tube multiple times before being entrained, velocity of abrasive water jet is given as,
V awj = η*)*V wj .
Where η= momentum loss factor
R= loading factor= mass flow rate of abrasive/ mass flow rate of water
Vwj= velocity of water jet.
8. There are _____ different types of suspension abrasive water jet .
a) 2
b) 3
c) 5
d) 7
Answer: b
Explanation: In suspension AWJM the abrasive water jet is formed quite differently. There are three different types of suspension AWJ formed by direct, indirect and Bypass pumping method.
9. In suspension AWJM, mixture of water and abrasive particles is pumped to high pressure.
a) True
b) False
Answer: a
Explanation: In suspension AWJM, preformed mixture of water and abrasive particles is pumped to sufficiently high pressure and store in pressure vessel. Then the premixed high-pressure water and abrasive is allowed to discharge from a nozzle to form abrasive water jet.
10. Catcher is used to_____
a) increase the residual energy of the AWJ
b) absorb the residual energy of the AWJ
c) focus the jet on the target
d) collect the residual part of the machined component
Answer: b
Explanation: Once the abrasive jet has been used for machining, they may have sufficiently high level of energy depending on the type of application. Such high-energy abrasive water jet needs to be contained before they can damage any part of the machine or operators. “Catcher” is used to absorb the residual energy of the AWJ and dissipate the same.
This set of Manufacturing Processes Question Bank focuses on “Abrasive Jet Micromachining – 14”.
1. How many types of catcher are there?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: Moreover the catcher can be of pocket type or line type. In pocket type, the catcher basin travels along the jet. In line type, the catcher basin only travels along one axis of the CNC table and its length covers the width of the other axis of the CNC table.
2. Which of the following is not true about entrained type AJWM?
a) Sapphires is used for orifice
b) Pressure range = 2500-4000 bars
c) Impact angle < 50 o
d) Depth of cut reached is 1—250 mm
Answer: c
Explanation: The general domain of parameters in entrained type AWJ machining system is given below:
• Orifice – Sapphires – 0.1 to 0.3 mm
• Focussing Tube – WC – 0.8 to 2.4 mm
• Pressure – 2500 to 4000 bar
• Abrasive – garnet and olivine – #125 to #60
• Abrasive flow – 0.1 to 1.0 Kg/min
• Stand-off distance – 1 to 2 mm
• Machine Impact Angle – 60 o to 90 o
• Traverse Speed – 100 mm/min to 5 m/min
• Depth of Cut – 1 mm to 250 mm.
3. In AWJM of ductile materials, material is mainly removed by _____ impact by abrasive particles.
a) low angle
b) 50 o —60 o
c) 65 o —70 o
d) 70 o —82 o
Answer: a
Explanation: Mechanism of material removal in machining with water jet and abrasive water jet is rather complex. In AWJM of ductile materials, material is mainly removed by low angle impact by abrasive particles leading to ploughing and micro cutting.
4. At higher angle of impact, the material removal involves _____ failure.
a) plastic
b) ductile
c) brittle
d) tensile
Answer: a
Explanation: At higher angle of impact, the material removal involves plastic failure of the material at the sight of impact, which was studied initially by a person named Bitter.
5. In case of AWJM of brittle materials, the material is removed due to crack formation.
a) True
b) False
Answer: a
Explanation: In case of AWJM of brittle materials, other than the above two models, material would be removed due to crack initiation and propagation because of brittle failure of the material.
6. When the kerf formed by the impact of the jet, the top of the kerf _____ than bottom of the kerf.
a) wider
b) longer
c) narrower
d) smoother
Answer: a
Explanation: The cut generated by an AWJM in different sections is called a kerf. The top of the kerf is wider than the bottom of the kerf. Generally, the top width of the kerf is equal to the diameter of the AWJ.
7. The taper angle of the kerf can be_____ of the AWJ
a) reduced by increasing the cutting ability
b) increased by increasing the cutting ability of the
c) reduced by decreasing the cutting ability of the
d) taper angle is not a function of the cutting ability of the jet
Answer: a
Explanation: The taper angle of the kerf can be reduced by increasing the cutting ability of the AWJ. It can be said that the surface quality at the top of the kerf is rather good compared to the bottom part. At the bottom there is repeated curved line formation.
8. Which of the following is true about AWJM?
a) At the bottom of the kerf, the material removal is by low angle impact of the abrasive particles
b) At the top of the kerf, the material removal is by low angle impact of the abrasive particles
c) At the top of the kerf, the material removal is by plastic failure
d) Striation formation occurs due to excess use of abrasive particles
Answer: b
Explanation: At the top of the kerf, the material removal is by low angle impact of the abrasive particle; whereas at the bottom of the kerf it is by plastic failure. Striation formation occurs due to repeated plastic failure.
9. Striation factor is an important product quality parameter in AWJM.
a) True
b) False
Answer: a
Explanation: In AWJM, following are the important product quality parameters;
• striation formation
• surface finish of the kerf
• tapering of the kerf
• burr formation on the exit side of the kerf.
10. Which of the following issues is not of much concern in AWJM?
a) Coolant recovery
b) Abrasive recovery
c) Spent water disposal
d) Chip recovery
Answer: a
Explanation: Nowadays, every manufacturing process is being re-evaluated in terms of its impact on the environment. The environmental issues relevant to AWJM are,
• water recycling
• spent water disposal
• chip recovery
• abrasive recovery and reuse.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Ultrasonic Machining – 1”.
1. Ultrasonic machining can be classified as which of the following type of non-traditional machining process?
a) electrical
b) optical
c) mechanical
d) chemical
Answer: c
Explanation: Ultrasonic machining is a non-traditional machining process. USM is grouped under the mechanical group NTM processes. In ultrasonic machining, a tool of the desired shape vibrates at an ultrasonic frequency.
2. Which of the following material is not generally machined by USM?
a) Copper
b) Glass
c) Silicon
d) Germanium
Answer: a
Explanation: USM is mainly used for machining brittle materials which are poor conductors of electricity and thus cannot be processed by Electrochemical and Electro-discharge machining.
3. Tool in USM is generally made from which of the following materials?
a) Glass
b) Ceramic
c) Carbides
d) Steel
Answer: d
Explanation: The tool material should be such that indentation by the abrasive grits does not lead to brittle failure. Thus the tools are made of tough, strong and ductile materials like steel, stainless steel and other ductile metallic alloys.
4. Under what frequency ultrasonic machining is done?
a) 5—10 Hz
b) 5—10 kHz
c) 12—19 Hz
d) 19—25 kHz
Answer: d
Explanation: Ultrasonic machining is a mechanical type non-traditional machining process. In ultrasonic machining, a tool of desired shape vibrates at an ultrasonic frequency of around 19—25 kHz with an amplitude of around 15 – 50 μm over the workpiece.
5. In ultrasonic machining , the tool is pressed downward.
a) True
b) False
Answer: a
Explanation: Generally the tool is pressed downward with a feed force. Between the tool and workpiece, the machining zone is flooded with hard abrasive particles generally in the form of water based slurry.
6. In ultrasonic machining, the abrasive particles act as the __________
a) chip carriers
b) intenders
c) finishing particles
d) thickening agent for the slurry
Answer: b
Explanation: During ultrasonic machining, as the tool vibrates over the workpiece, the abrasive particles act as the indenters and indent both the work material and the tool.
7. In case of brittle materials, the material is removed by crack initiation.
a) True
b) False
Answer: a
Explanation: The abrasive particles, as they indent, the work material, would remove the same, particularly if the work material is brittle, due to crack initiation, propagation and brittle fracture of the material.
8. During USM, cracks are produced due to _____
a) von-mises stresses
b) hertzian stresses
c) principal stresses
d) episodic acute stresses
Answer: b
Explanation: During USM, as the tool vibrates, it leads to the indentation of the abrasive grits. During indentation, due to hertzian contact stresses, cracks would develop just below the contact site then as indentation progresses the cracks would propagate due to increase in stress and ultimately lead to brittle fracture of the work material under each individual interaction site between the abrasive grits and the workpiece.
9. In USM, material removal may occur due to _____
a) fatigue failure
b) fouling failure
c) free flowing impact of the abrasive
d) creep
Answer: c
Explanation: Other than brittle failure of the work material due to indentation some material removal may occur due to free flowing impact of the abrasives against the work material and related solid-solid impact erosion, but it is estimated to be rather insignificant.
10. Increasing volume concentration of abrasive in slurry would affect MRR in which of the following manner?
a) increase MRR
b) decrease MRR
c) would not change MRR
d) initially decrease and then increase MRR
Answer: a
Explanation: The concentration of abrasive grits in the slurry is related as follow
n = / πd g 2 ,
where n= number of grits
A= total surface area of the tool facing the workpiece
C= concentration of abrasive grits in the slurry
d g = diameter of a grit
Thus above relation shows that any increase in ‘C’ will increase ‘n’ and hence material removal rate .
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Ultrasonic Machining – 2”.
1. Which of the following materials is not used as abrasive in ultrasonic machining?
a) SiC
b) Boronsilicarbide
c) Diamond
d) TiC
Answer: d
Explanation: Abrasive materials used as abrasive in USM are as follows;
• Al 2 O 3
• SiC
• B 4 C
• Boronsilicarbide
• Diamond.
2. Pick the odd one out.
a) Frequency of vibration
b) Abrasive size
c) Coolant flow rate
d) Flow strength of work material
Answer: c
Explanation: The process parameters which govern the ultrasonic machining process are listed below;
• Amplitude of vibration – 15 – 50 μm
• Frequency of vibration – 19 – 25 kHz
• Feed force – related to tool dimensions
• Feed pressure
• Abrasive size – 15 μm – 150 μm
• Flow strength of work material
• Flow strength of the tool material
• Contact area of the tool
• Volume concentration of abrasive in water slurry
• Abrasive material.
3. Which of the following is not the component of USM machine?
a) Slurry delivery
b) Transducer
c) Concentrator
d) Lead screw
Answer: d
Explanation: The typical elements of a USM are as follows;
• Slurry delivery and return system
• Feed mechanism to provide a downward feed force on the tool during machining
• The transducer, which generates the ultrasonic vibration
• The horn or concentrator.
4. In USM, horn is used for amplifying the vibrations.
a) True
b) False
Answer: a
Explanation: The horn or concentrator in USM mechanically amplifies the vibration to the required amplitude of 15 – 50 μm and accommodates the tool at its tip.
5. The transducer for USM works on how many principles?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: The ultrasonic vibrations are produced by the transducer. The transducer is driven by suitable signal generator followed by a power amplifier. The transducer for USM works on the following principle
• Piezoelectric effect
• Magnetostrictive effect
• Electrostrictive effect.
6. The horn or concentrator can have how many different shapes?
a) 2
b) 5
c) 3
d) It can have any shape
Answer: c
Explanation: The horn or concentrator is a wave-guide, which amplifies and concentrates the vibration to the tool from the transducer. The horn or concentrator can be of different shape like
• Tapered or conical
• Exponential
• Stepped.
7. Which of the following is not machined by USM?
a) Brittle metals
b) Glass
c) Ceramics
d) Ductile materials
Answer: d
Explanation: USM is used for machining;
• hard metallic alloys
• brittle metallic alloys
• semiconductors
• glass
• ceramics
• carbides.
8. For which of the following operations USM is not used?
a) Round shaped hole
b) Square shaped hole
c) Irregular shaped hole
d) Boring
Answer: d
Explanation: USM is used for machining;
• round shaped holes
• square shaped holes
• irregular shaped holes
• surface impressions.
9. USM has low material removal rate.
a) True
b) False
Answer: a
Explanation: Limitations of USM are as follows;
• Low MRR
• Rather high tool wear
• Low depth of hole.
10. USM machine uses _____ axis table.
a) single
b) 2
c) 3
d) 5
Answer: b
Explanation: The basic mechanical structure of a USM is very similar to a drill press. However, it has additional features to carry out USM of brittle work material. The workpiece is mounted on a vice, which can be located at the desired position under the tool using a 2 axis table. The table can further be lowered or raised to accommodate work of different thickness.
This set of Manufacturing Processes Questions and Answers for Entrance exams focuses on “Ultrasonic Machining – 3”.
1. USM is a material removal process used to _____ material.
a) corrode
b) erode
c) melt
d) form
Answer: b
Explanation: It is a material removal process, used to erode material in the form of fine holes and cavities in hard or brittle workpieces. It uses formed tools, vibrations of high frequency and suitable abrasive slurry-mix.
2. During USM, the workpiece is thermally affected.
a) True
b) False
Answer a
Explanation: USM is a non-thermal and non-chemical process which creates no change in the chemical, physical or metallurgical properties of the work piece. It is therefore, widely used in the manufacturing of hard and brittle materials, which are commonly infeasible to a machine by other non-traditional methods.
3. In USM, material removal occurs due to _____
a) abrading action
b) corroding action
c) chemical action
d) chip formation
Answer: a
Explanation: Ultrasonic machining accomplishes the material removal through the abrading action of the grit-loaded slurry which is kept circulated between the tool and the workpiece. The cutting is actually performed by the abrasive particles which are suspended in the slurry.
4. During USM, which of the following vibrates at ultrasonic frequency?
a) Slurry mix
b) Workpiece
c) Tool
d) Abrasive particles only
Answer: c
Explanation: The tool is vibrated at ultrasonic frequency and this will be in the range of 20 kHz. The slurry is made to flow through this in this zone so that the abrasive particles will come in contact with the workpiece.
5. Material removal in USM can be attributed to _____ mechanisms.
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: Following are the mechanisms that could be attributed to the material removal in USM;
• Hammering, that causes brittle fracturing of the work material
• Impact action of abrasives
• Cavitation.
6. The development of USM was started in _____
a) 1920
b) 1927
c) 1947
d) 1980
Answer: b
Explanation: The development of USM was started in 1927. It was accidentally discovered during investigating the ultrasonic grinding of abrasive powders.
7. The abrasive grains are driven by the reciprocations across the gap in between the tool and the work piece.
a) True
b) False
Answer: a
Explanation: The abrasive grains are driven by the high speed reciprocations across the small gap in between the tool and the work piece, as already discussed. Uniform force is used to gradually feed the tool. The impact of the abrasive is the energy source that is mainly responsible for material removal. Due to the impact of abrasives, the material removal takes place in the form of small particles, which are carried away by the abrasives slurry.
8. Which of the following is true about USM?
a) There is direct contact between the tool and the workpiece
b) There is no direct contact between the tool and the workpiece
c) This process is not suitable for machining of brittle materials
d) This process consumes very less power
Answer: b
Explanation: There is no direct contact of the tool and the work piece due to the slurry used and it makes it a wet cutting process the surfaces so produced are free from stress and damages. This process is free from burrs and distortions. However, the process is very much suitable for machining brittle materials.
9. Which of the following materials is not suitable for USM?
a) Lead
b) Glass
c) Ceramic
d) Carbides
Answer: a
Explanation: Soft materials like lead and plastics are not suitable for machining by this process, since that they tend to absorb the abrasive particles rather than the chip under the impact.
10. During USM __________ is converted into mechanical vibrations.
a) pressure energy of the slurry
b) electrical energy
c) chemical energy of the chemical used for the slurry
d) mechanical energy of the tool
Answer: b
Explanation: During USM, high frequency electrical energy is converted into mechanical vibrations through a transducer. The high frequency vibrations are transmitted to the abrasive particles in the slurry via an energy focusing device called horn or tool assembly.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Ultrasonic Machining – 4”.
1. Which of the following is true about USM?
a) In USM, tool needs to be changed frequently
b) USM consumes less power
c) USM can be used for soft materials
d) In USM, workpiece is vibrated at ultrasonic frequency
Answer: a
Explanation: In USM tool needs to be replaced more frequently because;
• the tool end is susceptible for wear during the process
• soft corners of the tool get rounded off quickly
Due to these reasons, generally hard material like steel is used for the tool.
2. In USM, the bottom surfaces of blind holes tend to become concave due to _____
a) insufficient slurry circulation
b) resistance to abrasive particles
c) ineffective slurry circulation
d) high frequency of the vibrations
Answer: c
Explanation: The holes produced in ultrasonic machining have a tendency to break out at the bottom owing to the static load and high amplitudes. While producing deeper holes through USM method, there is ineffective slurry circulation leading to the presence of the fewer active grains under the tool face. Due to this, the bottom surfaces of the blind holes tend to become slightly concave.
3. Which of the following pumps is used in USM?
a) Re-circulating pump
b) Centrifugal pump
c) Vane pump
d) Reciprocating pump
Answer: a
Explanation: In USM, A re-circulating pump forces abrasive suspended in a liquid medium between the vibrating tool face and work piece. Then the tool shaped like the cavity to be produced oscillates at amplitude of about 0.013 to 0.062 mm at 19 to 40 kilo hertz. The tool vibrates abrasive grains against the surface of the work piece, thus removing the material.
4. Which of the following is not a part of the ultrasonic machine used in USM?
a) Generator
b) Acoustic head
c) Slurry pump
d) Lead-screw
Answer: d
Explanation: The basic ultrasonic equipment consists of, a generator for high frequency oscillations; an acoustic head, consisting of a transducer and a horn also known as shank or trunk; also, tool and abrasive slurry elements like pump and tank for slurry.
5. The primary purpose of the transducer is _____
a) to make uniform mixture of the slurry and the abrasive particles
b) to take filter the slurry after the operation
c) to convert energy
d) to cool the tool
Answer: c
Explanation: The generator is responsible for transmitting electrical power to the transducer, which creates energy impulses in the ultrasonic range. That is sometimes starting from 18 kilo hertz onwards. The energy pluses are then converted into mechanical vibrations. The primary function of the transducer is to convert these electrical impulses into vertical and two dimensional strokes. Sometimes it can be horizontal as well, depending on the configuration of the machine.
6. The acoustic head consists of how many parts?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: The acoustic head is considered as the heart of the whole equipment and this mainly consists of two parts. The transducer, which converts the high frequency output of the generator into linear vibrations, the number two the horn or the trunk, which mechanically amplifies the linear vibrations.
7. Which of the following is not the alternative name for the trunk in USM?
a) horn
b) concentrator
c) shaft
d) shank
Answer: c
Explanation: It is a critical link in the ultrasonic machining system. This is known by several names such as shank, horn, concentrator and amplifier as well. The trunk amplifies and focuses vibration of the transducer to require the intensity, necessary enough for driving the tool.
8. Tool in USM is subjected to vibratory loads.
a) True
b) False
Answer: a
Explanation: The tools are designed to provide the maximum amplitude of vibration at the free end, the selection of the tool material is very important as the tool tip is subjected to vibration and it must not fail due to wear.
9. The tool is joined to the trunk by _____
a) riveted joint
b) welded joint
c) brazing
d) honing
Answer: c
Explanation: The tool is attached to the trunk or the horn by silver brazing process. At times it is fasten or the screwed to the trunk also. The commonly used tool materials are brass, high speed steel, mild steel, silver, stainless steel, tungsten carbide and monel metal.
10. Tool geometry does not affect the performance of the USM process.
a) True
b) False
Answer: b
Explanation: The shape of the tool , mechanical properties of the materials used in tool making are some of the parameters that may affect the performance of the USM process significantly.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Friction Welding – 1”.
1. Friction welding produces welds due to ______
a) electrode melting
b) workpiece melting
c) relative motion between workpieces
d) adhesive force between workpiece particles
Answer: c
Explanation: Friction Welding is a solid state welding process which produces welds due to the compressive force contact of workpieces which are either rotating or moving relative to one another.
2. In friction welding, material is deformed due to_____
a) elastic deformation
b) plastic deformation
c) ductile deformation
d) brittle deformation
Answer: b
Explanation: In friction welding the heat required to produce the joint is generated by friction heating at the interface. This heat displaces material plastically from the faying surfaces.
3. Which of the following is true about friction welding?
a) One workpiece is held stationary while the other is moving
b) Both the workpieces are moving
c) Both the workpieces are stationary and filler is added in the space between them
d) The material is deformed elastically
Answer: a
Explanation: The components to be joined are first prepared to have smooth, square cut surfaces. One piece is held stationary while the other is mounted in a motor driven chuck or collet and rotated against it at high speed.
4. During friction welding, initially low pressure is applied. Why?
a) For slowly increasing the surface temperature
b) For melting the surface coating on the materials
c) To check weldabilty of two materials
d) For initial cleaning of the surface
Answer: d
Explanation: A low contact pressure may be applied initially to permit cleaning of the surfaces by a burnishing action. This pressure is then increased and contacting friction quickly generates enough heat to raise the abutting surfaces to the welding temperature.
5. After the welding temperature is reached _____
a) rotation is stopped
b) speed of rotation is increased
c) rotation of first workpiece is stopped and second workpiece starts rotating
d) filler material is added
Answer: a
Explanation: As soon as the welding temperature is reached, rotation is stopped and the pressure is maintained or increased to complete the weld. The softened material is squeezed out to form a flash. If desired, the flash can be removed by subsequent machining action.
6. By friction welding, steel bars upto _____ mm diameter can be welded.
a) 10
b) 50
c) 100
d) 210
Answer: c
Explanation: During friction welding, a forged structure is formed in the joint. Friction welding has been used to join steel bars upto 100 mms in diameter and tubes with outer diameter upto 100 mm.
7. Inertia welding is a modified form of friction welding.
a) True
b) False
Answer: a
Explanation: Inertia welding is a modified form of friction welding, where the moving piece is attached to a rotating flywheel. The flywheel is brought to a specified rotational speed and is then separated from the driving motor.
8. Which of the following is not true about inertia welding?
a) Weld is formed when the flywheel stops
b) The process is difficult for automation
c) Weld quality is consistent
d) Parts remain in contact even after the weld is completed
Answer: b
Explanation: The weld is formed when the flywheel stops its motion and the pieces remain pressed together. Since the conditions of the inertia welding are easily duplicated, welds of consistent quality can be produced and the process can be easily automated.
9. During friction welding, shielding gases are needed.
a) True
b) False
Answer: a
Explanation: Following are the advantages of friction welding;
• No filler material is needed
• No shielding gases or flux is needed
• It is smoke free process
• The process is in solid state with a narrow heat affected zone.
10. Which of the following is not true?
a) Oxides can be removed after the welding process
b) Automation is possible
c) Rapid welds are made
d) Process can be used for limited materials
Answer: d
Explanation: Following are the advantages of friction welding;
• Oxides can be removed after the welding process
• In most cases, the weld strength is stronger that the weaker of the two materials
• The process can be easily automated for mass production
• The process is very efficient and comparatively very rapid welds are made
• Wide variety of metals and combinations can be welded.
This set of Manufacturing Processes Questions and Answers for Campus interviews focuses on “Friction Welding – 2”.
1. Friction welding process is restricted to_____
a) square bars
b) round bars
c) hexagonal bars
d) bars having diameters less than 20mm
Answer: b
Explanation: The process is restricted to joining round bars of same diameter , i.e., capable of being rotated about the axis. Furthermore, capital equipment and tooling costs are high and free-machining alloys are difficult to weld.
2. Which of the following materials cannot be welded by friction welding?
a) Aluminium
b) Copper
c) Stainless steel
d) Non-forgeable materials
Answer: d
Explanation: Dry bearing and non-forgeable materials cannot be welded by a friction welding process, i.e., one of the components must be ductile when hot, to permit deformations. Preparation and alignment of the workpieces of the workpieces may be critical for developing for developing uniform rubbing and heating, particularly for pieces having diameters larger than 50mm.
3. In which of the following areas, friction welded products are not used?
a) Aerospace
b) Automotive
c) Marine
d) Toy making
Answer: d
Explanation: Friction welded parts in production application span over wide products for aerospace, agriculture, automotive, defence, marine and oil industries. Right from tong holds to critical aircraft engine components are friction welded in production.
4. Which of the following automotive components are not friction-welded?
a) Gears
b) Engine valves
c) Strut rods
d) Rims
Answer: d
Explanation: Automotive parts that are friction welded include gears, engine valves, axel tubes, driveline components, strut rods and shock absorbers. Rims are generally welded by TIG or MIG welding.
5. Friction welding cannot be used for welding stainless steel to carbon steels.
a) True
b) False
Answer: b
Explanation: Stainless steels are friction welded to carbon steels in various sizes for uses in marine systems and water pumps for home and industrial use. Friction welded aluminium/copper joints are in wide usage in the electrical industry.
6. Friction welded components are cheaper than casted components.
a) True
b) False
Answer: b
Explanation: Friction welded components are comparatively cheaper than casted components. Friction welded assemblies are often used to replace expensive casted and forged components.
7. Which of the following components from agricultural equipment is not friction welded?
a) Track rollers
b) Axles
c) Bushings
d) Cultivator
Answer: d
Explanation: Following are the few components which are friction welded by manufacturers of agricultural equipment;
• Hydraulic piston rods
• Track rollers
• Gears
• Bushings
• Axles
Cultivators are heavy duty machines used for soil cultivation.
8. Aluminium is difficult to friction weld because of _____
a) ductility
b) softness
c) micro porosity
d) heat reflectivity
Answer: c
Explanation: The basic problems with friction welding of aluminium and its alloys are that they possess:
• Cast brittle dendritic structure
• Micro porosity
• Loss of strength in heat affected zone
• Solidification and liquation cracking
• Fatigue properties.
9. Which of the following processes can be used as alternative technique for joining aluminium and its alloys?
a) Tungsten inert-gas welding
b) Metal inert-gas welding
c) Friction stir welding
d) Oxy-Acetylene flame technique
Answer: c
Explanation: The following alternate techniques are being used for joining of aluminium and its alloys:
• Electron beam welding
• Laser beam welding
• Variable polarity plasma arc welding
• Friction stir welding.
10. Which of the following is not true about friction stir welding?
a) It is a solid state process
b) Fine grained structures can be obtained
c) It eliminates friction welding problems
d) It alters the chemical composition of the workpiece
Answer: d
Explanation: Following are the advantages of friction stir welding:
• It is a solid state process
• Fine grained, re-crystallized microstructures can be obtained
• It eliminates friction welding problems
• There is no significant alteration of chemical composition
• Routinely used to join difficult to friction weld alloys.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Friction Welding – 3”.
1. In friction welding process, materials are joined by _____ motion between materials.
a) rectilinear
b) rubbing
c) translatory
d) brownian
Answer: b
Explanation: Friction welding is a solid-state joining process that produces coalescence in materials, using the heat developed between surfaces through a combination of mechanically induced rubbing motion and applied load. The resulting joint is of forged quality.
2. All metallic engineering materials which are _____ can be friction welded.
a) soft
b) weldable
c) forgeable
d) metamaterials
Answer: c
Explanation: As a rule, all metallic engineering materials which are forgeable can be friction welded, including automotive valve alloys, maraging steel, tool steel, alloy steels and tantalum. In addition, many castings, powder metals and metal matrix composites are weldable.
3. Friction welding is _____ process.
a) costly
b) cost saving
c) time consuming
d) highly material selective
Answer: b
Explanation: Since dissimilar materials can be joined, a significant cost savings are possible because engineers can design bimetallic parts that use expensive materials only where needed. Expensive forgings and castings can be replaced with less expensive forgings welded to bar stock, tubes, plates and the like.
4. Friction welding produces quality joints, with a 100% _____ weld.
a) lap joint
b) tee-joint
c) butt joint
d) edge joint
Answer: c
Explanation: Friction welding produces forged quality joints, with a 100% butt joint weld through the contact area. Furthermore, in friction welding heat affected zone is much narrower as compared to other welds, which indeed reduces the cost of post-weld heat treatments .
5. Which of the following is not true about friction welding?
a) Dissimilar metals cannot be joined
b) This technique is relatively faster as compared to the other techniques
c) This technique is suitable for any parts of shape or size
d) Sheared surfaces can also be joined by the process
Answer: a
Explanation: Following are the few advantages of friction welding over other techniques:
• Dissimilar metals are joined, even some considered incompatible or unweldable.
• The process is at least twice— and up to 100 times—as fast as other welding techniques.
• Friction welders are versatile enough to join a wide range of part shapes, materials and sizes.
• Joint preparation isn’t critical… machined saw cut, and even sheared surfaces are weldable.
6. Which of the following holds true for friction welding?
a) Hazardous fumes are generated during the process
b) Argon is used as a shielding gas
c) It is a power consuming process
d) There are no solidification defects in the welded parts
Answer: d
Explanation: Following are the few reasons to consider friction welding over other techniques:
• The machine-controlled process eliminates human error, and weld quality is independent of operator skill.
• It’s ecologically clean—no objectionable smoke, fumes, or gases are generated that need to be exhausted.
• No consumables are required— no flux, filler material, or shielding gases.
• Power requirements are as low as 20% of that required of conventional welding processes.
• Since there is no melting, no solidification defects occur, e.g. gas porosity, segregation or slag inclusions.
7. In inertia friction welding ______ energy of welding machine is used.
a) electrical
b) potential
c) rotational
d) frictional
Answer: c
Explanation: Inertia Friction Welding is a variation of friction welding in which the energy required to make the weld is supplied primarily by the stored rotational kinetic energy of the welding machine.
8. In inertia friction welding, one workpiece is connected to _____
a) flywheel
b) the pin tool
c) rotor
d) generator
Answer: a
Explanation: In Inertia Welding, one of the workpieces is connected to a flywheel and the other is restrained from rotating. The flywheel is accelerated to a predetermined rotational speed, storing the required energy. The drive motor is disengaged and workpieces are forced together by the friction welding force.
9. Weld strength in inertia friction welding is more than direct drive friction welding.
a) True
b) False
Answer: a
Explanation: Inertia Friction Welding has the following advantages over the Direct Drive Friction Welding process:
• Helical flow lines and hot working at end of weld cycle can help in weld strength
• Ease of monitoring, given only two variables for welding: energy and pressure. Energy can be monitored before a signal is given to weld reducing the variables during welding to one
• Weld torque is measured indirectly by measuring the rate of spindle speed change.
10. In direct drive friction welding, lower weld forces are generated.
a) True
b) False
Answer: a
Explanation: Following are the advantages of direct drive friction welding over inertia friction welding:
• Lower weld force for solid parts. Larger parts can be welded on same tonnage machine
• Lower weld torque if brake is applied at end of weld cycle. Tooling requirements are, therefore, less rigid
• Lower RPM for solid parts
• No flywheel change between setups.
This set of Manufacturing Processes Questions and Answers for Aptitude test focuses on “Friction Welding – 4”.
1. In Direct Drive Friction Welding, energy is supplied by _____
a) an electromagnet
b) a capacitor
c) an electric motor
d) a heating unit called heater
Answer: c
Explanation: Direct Drive Friction Welding is a variation of friction welding in which the energy required to make the weld is supplied by the welding machine through a direct motor connection for a preset period of the welding cycle.
2. Which of the following holds true about direct drive friction welding?
a) Both the workpieces are restrained from motion
b) Among two workpieces, the one attached to motor-driven unit is restrained from motion
c) Among two workpieces, the one which is not attached to motor-driven unit is restrained from motion
d) Both the workpieces are moving relative to each other
Answer: c
Explanation: In Direct Drive Friction Welding, one of the workpieces is attached to a motor-driven unit while the other is restrained from rotation. The motor-driven workpiece is rotated at a predetermined constant speed.
3. _____ generated during friction welding is coherent.
a) Burr
b) Molten metal
c) Flash curl
d) Fly ash
Answer: c
Explanation: The flash curl generated during welding is coherent, will not flake off, and can often be left intact if design and engineering considerations allow. Alternately, parts can frequently be designed to accommodate the flash curl in a recess .
4. Part geometry and accessibility of the flash are the factors which decide flash removal process.
a) True
b) False
Answer: a
Explanation: In many cases, if the weld flash must be removed, this can be accomplished on the welder as an integrated part of the machine cycle. Part geometry and accessibility of the flash are the two major factors which determine whether on-machine flash removal can be incorporated, and which system can be employed.
5. How many flash removal systems are there?
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: Available systems are:
• Shearing–outside
• Shearing–inside
• Plunge Cut–one axis
• Plunge Cut–two axis.
6. Which of the following components of an aircraft is/are not friction welded?
a) Gears
b) Hooks bolt
c) Shafts
d) Hydraulic cylinders
Answer: d
Explanation: Aircraft/ aerospace components which are friction welded include compressor rotors, fan shafts, cluster gears, landing gear components, bi-metallic rivets and hook bolts, aluminium heat pipes, and cryogenic rocket components.
7. Friction welding one of the leading methods of joining different metals.
a) True
b) False
Answer: a
Explanation: Proven reliability of friction welded connections, coupled with the process advantages such as being clean, fast, consistent, and free of operator-induced error, makes friction welding one of the leading methods of joining flanges to valve bodies, drill pipe, high-pressure hose couplings, and manifold tubes.
8. Friction welding produces a _____ bond.
a) metallic
b) metallurgical
c) ionic
d) co-ordinate
Answer: b
Explanation: Friction welding produces a metallurgical bond strong enough to take the high torque and highly loaded rotary tension due to directional drilling.
9. Which of the following is not the advantage of friction welding?
a) No smoke generation during the process
b) Less sparks are produced during the process
c) Applicable for all metals
d) Time saving process
Answer: c
Explanation: The advantages of this process such as no smoke, fumes or gases, or few sparks produced, and the fact that the process is machine-controlled, make it suitable for use in potentially explosive or hazardous environments. The machine can be fully automated so the operator can be safely located out of harm’s way. This process is not applicable to non-forgeable metals.
10. Which of the following set is not joined by friction welding process?
a) Aluminium to Steel
b) Copper to Aluminium
c) Copper to Titanium
d) Rubidium to Caesium
Answer: d
Explanation: Metal combinations not normally considered compatible are joined by friction welding, such as aluminium to steel, copper to aluminium, titanium to copper, and nickel alloys to steel.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electron Beam Machining – 1”.
1. Mechanism of material removal in Electron Beam Machining is due to _____
a) mechanical erosion due to impact of high of energy electrons
b) chemical etching by the high energy electron
c) sputtering due to high energy electrons
d) melting and vaporisation due to the thermal effect of impingement of high energy electron
Answer: d
Explanation: EBM is typically used with higher power density to machine materials. The mechanism of material removal is primarily by melting and rapid vaporisation due to intense heating by the electrons and laser beam respectively.
2. Electron beam machining is a/an _____ process
a) adiabatic
b) thermal
c) iso-thermal
d) isentropic
Answer: b
Explanation: Electron Beam Machining is a thermal process considering the mechanisms of material removal. However electrical energy is used to generate high-energy electrons in case of Electron Beam Machining .
3. Electron beam machining is carried out in _____
a) high pressure vessel
b) thermally insulated area
c) vacuum
d) in a room at atmospheric pressure
Answer: c
Explanation: Electron Beam Machining is required to be carried out in vacuum. Otherwise, the electrons would interact with the air molecules, thus they would lose their energy and cutting ability.
4. During EBM _____ is kept under vacuum.
a) electron gun
b) whole setup
c) the workpiece
d) laser generation setup
Answer: c
Explanation: The workpiece to be machined is located under the electron beam and is kept under vacuum. The high-energy focused electron beam is made to impinge on the workpiece with a spot size of 10 – 100 μm.
5. As the electrons strike the work material _____
a) heat energy is converted to kinetic energy
b) atomic energy is converted to heat energy
c) kinetic energy is converted to heat energy
d) electrical energy is converted to heat energy
Answer: c
Explanation: The kinetic energy of the high velocity electrons is converted to heat energy as the electrons strike the work material. Due to high power density instant melting and vaporisation starts and “melt – vaporisation” front gradually progresses.
6. The gun in EBM is used in _____ mode.
a) wave guide
b) biasing
c) pulsed
d) high intensity
Answer: c
Explanation: Unlike in Electron Beam Welding, the gun in EBM is used in pulsed mode. Holes can be drilled in thin sheets using a single pulse. For thicker plates, multiple pulses would be required. Electron beam can also be manoeuvred using the electromagnetic deflection coils for drilling holes of any shape.
7. Which of the following is not a function of electron beam gun?
a) generation of electrons
b) accelerating the electrons
c) focusing the beam
d) absorbing the electron beam
Answer: d
Explanation: Electron beam gun is the heart of any electron beam machining facility. The basic functions of any electron beam gun are to generate free electrons at the cathode, accelerate them to a sufficiently high velocity and to focus them over a small spot size. Further, the beam needs to be manoeuvred if required by the gun.
8. ______ is used to make cathode for electron beam gun.
a) Aluminium
b) Rubidium
c) Molybdenum
d) Tantalum
Answer: d
Explanation: The cathode is generally made of tungsten or tantalum. Such cathode filaments are heated, often inductively, to a temperature of around 2500⁰C.
9. Heating to a high temperature leads to thermo-ionic emission.
a) True
b) False
Answer: a
Explanation: In EBM, temperature in the electron beam gun is around 2500⁰C. Such heating leads to thermo-ionic emission of electrons, which is further enhanced by maintaining a very low vacuum within the chamber of the electron beam gun.
10. In the electron beam gun, cathode cartridge is highly negatively biased.
a) True
b) False
Answer: a
Explanation: In the electron beam gun, cathode cartridge is highly negatively biased so that the thermo-ionic electrons are strongly repelled away from the cathode. This cathode is often in the form of a cartridge so that it can be changed very quickly to reduce downtime in case of failure.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electron Beam Machining – 2”.
1. In electron beam machine, just after the cathode, there is/are _____
a) deflector coils
b) a magnetic lens
c) bias grid
d) port for vacuum gauge
Answer: c
Explanation: Just after the cathode, there is an annular bias grid. A high negative bias is applied to this grid so that the electrons generated by this cathode do not diverge and approach the next element, the annular anode, in the form of a beam.
2. Electron is accelerated by _____
a) cathode cartridge
b) electromagnetic coils
c) aperture
d) annular anode
Answer: d
Explanation: The annular anode now attracts the electron beam and gradually gets accelerated. As they leave the anode section, the electrons may achieve a velocity as high as half the velocity of light.
3. _____ determines the mode of an electron beam.
a) Applied voltage
b) Operating pressure
c) Position of magnetic lens
d) The nature of biasing
Answer: d
Explanation: The nature of biasing just after the cathode controls the flow of electrons and the biased grid is used as a switch to operate the electron beam gun in pulsed mode.
4. After the anode, the electron beam passes through _____
a) cathode cartridge
b) deflector coils
c) bias grid
d) a series of lenses
Answer: d
Explanation: After the anode, the electron beam passes through a series of magnetic lenses and apertures. The magnetic lenses shape the beam and try to reduce the divergence.
5. In the electron beam gun, apertures ______
a) allow only convergent electrons to pass
b) absorb convergent electrons
c) allow divergent electrons to pass
d) accelerate the electron beam
Answer: a
Explanation: The magnetic lenses shape the beam and try to reduce the divergence. Apertures on the other hand allow only the convergent electrons to pass and capture the divergent low energy electrons from the fringes. This way, the aperture and the magnetic lenses improve the quality of the electron beam.
6. In the final section of the electron beam gun, electron beam passes through the electromagnetic lens and deflection coil.
a) True
b) False
Answer: a
Explanation: After the apertures, the electron beam passes through the final section of the electromagnetic lens and deflection coil. The electromagnetic lens focuses the electron beam to the desired spot. The deflection coil can manoeuvre the electron beam, though by small amount, to improve the shape of the machined holes.
7. What is the purpose of a series of slotted rotating discs provided between the electron beam gun and the workpiece?
a) It increases the accuracy of the beam
b) It can increase the intensity of the beam
c) It prevents power losses
d) It prevents vapour generated during machining to reach the gun
Answer: d
Explanation: Generally in between the electron beam gun and the workpiece, which is also under vacuum, there would be a series of slotted rotating discs. Such discs allow the electron beam to pass and machine materials but helpfully prevent metal fumes and vapour generated during machining to reach the gun. Thus it is essential to synchronize the motion of the rotating disc and pulsing of the electron beam gun.
8. For alignment of the beam, _____ is provided.
a) a lens
b) a telescope
c) magnifier
d) microscope
Answer: b
Explanation: Electron beam guns are also provided with illumination facility and a telescope for alignment of the beam with the workpiece. Lens are provided to focus the beam.
9. The workpiece is mounted on a CNC table.
a) True
b) False
Answer: a
Explanation: In electron beam machining, the workpiece is mounted on a CNC table so that holes of any shape can be machined using the CNC control and beam deflection in-built in the gun.
10. Level of vacuum within the gun is in the order of _____
a) 10 -4 to 10 -6 Torr
b) 10 -1 to 10 -3 Torr
c) 10 -.0.65 to 10 -1 Torr
d) 1 to 2 Torr
Answer: a
Explanation: One of the major requirements of EBM operation of electron beam gun is maintenance of desired vacuum. Level of vacuum within the gun is in the order of 10 -4 to 10 -6 Torr {1 Torr = 1mm of Hg}.
This set of Manufacturing Processes Assessment Questions and Answers focuses on “Electron Beam Machining – 3”.
1. In electron beam gun, vacuum is achieved by _____
a) reciprocating pump
b) rotary pump only
c) combination of rotary pump and diffusion pump
d) combination of diffusion pump and vane pump
Answer: c
Explanation: Maintenance of suitable vacuum is essential so that electrons do not lose their energy. Such a vacuum is achieved and maintained using a combination of rotary pump and diffusion pump. Diffusion pump is attached to the diffusion pump port of the electron beam gun.
2. Diffusion pump is an _____
a) oil filter equipment
b) oil heater
c) oil cooler
d) oil collector
Answer: b
Explanation: Diffusion pump is essentially an oil heater. As the oil is heated the oil vapour rushes upward where gradually converging structure is present.
3. The oil coming out of diffusion pump is evacuated by a _____
a) screw pump
b) gear pump
c) rotary pump
d) piston pump
Answer: d
Explanation: The nozzles change the direction of motion of the oil vapour and the oil vapour starts moving downward at a high velocity as jet. This oil is evacuated by a rotary pump via the backing line.
4. High velocity gets of oil vapour coming out of diffusion pump entrain ______ present within the gun.
a) water droplets
b) oil droplets
c) air molecules
d) hazardous gas molecules
Answer: b
Explanation: High velocity jets of oil vapour coming out of the diffusion pump entrain any air molecules present within the gun. The oil vapour condenses due to the presence of a cooling water jacket around the diffusion pump.
5. Which of the following parameters do not affect the electron beam machining process?
a) Accelerating voltage
b) Lens current
c) Spot size
d) Workpiece material
Answer: d
Explanation: The process parameters, which directly affect the machining characteristics in Electron Beam Machining, are:
• The accelerating voltage
• The beam current
• Pulse duration
• Energy per pulse
• Power per pulse
• Lens current
• Spot size
• Power density.
6. For the electron beam machining process, pulse duration for the electron beam is in range of_____
a) 10 μs to 90 μs
b) 50 μs to 15 ms
c) 80 μs to 10 ms
d) 15 ms to 1 s
Answer: b
Explanation: EBM the gun is operated in pulse mode. This is achieved by appropriately biasing the biased grid located just after the cathode. Switching pulses are given to the bias grid so as to achieve a pulse duration of as low as 50 μs to as long as 15 ms.
7. Beam current is in the range of _____
a) 50 μamp to 0.8 amp
b) 100 μamp to 10 amp
c) 200 μamp to 1 amp
d) 185 μamp to 1.5 amp
Answer: c
Explanation: Beam current is directly related to the number of electrons emitted by the cathode or available in the beam. Beam current once again can be as low as 200 μamp to 1 amp.
8. Increasing the beam current directly increases the _____
a) energy per pulse
b) accelerating voltage
c) spot size
d) lens current
Answer: a
Explanation: Increasing the beam current directly increases the energy per pulse. Similarly, increase in pulse duration also enhances energy per pulse. High-energy pulses can machine larger holes on thicker plates.
9. In electron beam machining process, the energy density is controlled by spot size.
a) True
b) False
Answer: a
Explanation: The energy density and power density is governed by energy per pulse duration and spot size. Energy density varies inversely with the spot size, i.e., higher energy density means lower spot size.
10. At higher energy densities, material removal rate is high.
a) True
b) False
Answer: a
Explanation: Spot size, on the other hand is controlled by the degree of focusing achieved by the electromagnetic lenses. A higher energy density, i.e., for lower spot size, the material removal would be faster through the size of the hole would be smaller.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Electron Beam Machining – 4”.
1. In electron beam machining, the plane of _____ is on the surface of the workpiece.
a) focusing
b) finishing
c) heating
d) drilling
Answer: a
Explanation: The plane of focusing would be on the surface of the workpiece or just below the surface of the workpiece. This controls the kerf shape or the shape of the hole.
2. _____ can manoeuvre the electron beam.
a) Nozzles
b) Magnetic lens
c) Electromagnetic coils
d) Deflector coils
Answer: d
Explanation: In electron beam gun assembly, the final deflection coil can manoeuvre the electron beam which helps in generating holes of non-circular cross-section as required.
3. Electron beam machining process can machine holes of diameters in the range of _____
a) 10 μm to 80 μm
b) 50 μm to 100 μm
c) 100 μm to 2 mm
d) 2 mm to 5 mm
Answer: c
Explanation: Electron beam machining can provide holes of diameter in the range of 100 μm to 2 mm with a depth up to 15 mm, i.e., with a length/diameter ratio of around 10.
4. Which of the following is true about electron beam machining ?
a) By EBM process, tapered holes can be generated
b) Electro-magnetic coils are used to change the direction of the electron beam
c) Electron beam gun works under high pressure
d) Increasing the current density increases the spot size
Answer: a
Explanation: Electron beam machining can generate a hole which can be tapered along the depth or barrel shaped. By focusing the beam below the surface a reverse taper can also be obtained.
5. Which of the following holds true for electron beam machining?
a) This process does not generate burr
b) Holes having length/diameter ratio as high as 50 can be machined by this process
c) In electron beam gun, magnetic lens is used to diverge the beam
d) Electron beam is accelerated by electromagnetic coils
Answer: a
Explanation: Generally burr formation does not occur in electron beam machining. There would be an edge rounding at the entry point along with a presence of recast layer. Also, magnetic lens is used to focus the beam at a single point. Annular anodes are used to accelerate the beam.
6. Which of the following materials is not machined by the EBM process?
a) Titanium
b) Wood
c) Plastic
d) Leather
Answer: b
Explanation: Materials which can be machined by EBM are:
• Commercial grade steel
• Stainless steel
• Ti and Ni super alloys
• Aluminium plastics
• Ceramics
• Leathers.
7. For EBM process, heat affected zone is about _____
a) 10 μm to 80 μm
b) 20 μm to 30 μm
c) 100 μm to 1 mm
d) 2 mm to 5 mm
Answer: b
Explanation: In electron beam machining, the heat-affected zone is rather narrow due to the shorter pulse duration. Typically, the heat affected zone is around 20 μm to 30 μm.
8. Which of the following materials are easy to a machine by EBM process?
a) Aluminium
b) Steel
c) Plastic
d) Wood
Answer: a
Explanation: EBM can machine steel titanium alloys, aluminium, plastics, nickel alloys, etc., but some of the materials like Al and Ti alloys are more readily machined compared to steel.
9. Number of holes drilled per second depends on the holes diameter.
a) True
b) False
Answer: a
Explanation: Number of holes drilled per second depends on:
• hole diameter
• power density
• depth of the hole
• material type.
10. While machining, there are chances of thermal damage associated with EBM.
a) True
b) False
Answer: a
Explanation: As the mechanism of material removal is thermal in nature as for example in electro-discharge machining, there would be thermal damages associated with EBM. On the contrary, heat affected zone is narrow.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Beam Machining – 1”.
1. Mechanism of material removal in Laser Beam Machining is due to _____
a) mechanical erosion due to impact of high of energy photons
b) electro-chemical etching
c) melting and vaporisation due to thermal effect of impingement of high energy laser beam
d) fatigue failure
Answer: c
Explanation: Laser beam machining is carried out utilizing the energy of coherent photons or laser beam, which is mostly converted into thermal energy upon interaction with most of the materials.
2. Laser Beam is produced due to _____
a) spontaneous emission
b) stimulated emission followed by spontaneous emission
c) spontaneous emission followed by Spontaneous absorption
d) spontaneous absorption leading to “population inversion” and followed by stimulated emission
Answer: d
Explanation: Lasing process describes the basic operation of laser, i.e. generation of a coherent beam of light by “light amplification” using “stimulated emission”.
3. Which of the following processes does not use lasers?
a) Cladding
b) Alloying
c) Nitriding
d) Cutting
Answer: c
Explanation: Laser Beam Machining or more broadly laser material processing deals with machining and material processing like heat treatment, alloying, cladding, sheet metal bending, etc.
4. Lasers are also used for_____
a) riveting
b) nitriding
c) rapid prototyping
d) facing
Answer: c
Explanation: Nowadays, laser is also finding application in regenerative machining or rapid prototyping as in processes like stereo-lithography, selective laser sintering etc.
5. Laser stands for light amplification by stimulated emission of radiation.
a) True
b) False
Answer: a
Explanation: Laser stands for light amplification by stimulated emission of radiation. The underline working principle of a laser was first put forward by Albert Einstein in 1917 through the first industrial laser for experimentation was developed around the 1960s.
6. Laser beams can have power density upto _____
a) 1 kW/mm 2
b) 10 kW/mm 2
c) 1 MW/mm 2
d) 10 MW/mm 2
Answer: c
Explanation: Laser beam can very easily be focused using optical lenses as their wavelength ranges from half micron to around 70 microns. Focussed laser beam as indicated earlier can have power density in excess of 1 MW/mm 2 .
7. Laser causes a rapid substantial rise in _____ of the material.
a) local temperature
b) local pressure
c) indentation
d) cracks
Answer: a
Explanation: As laser interacts with the material, the energy of the photon is absorbed by the work material leading to rapid substantial rise in local temperature. This in turn results in melting and vaporisation of the work material and finally material removal.
8. At _____ temperature an atom is considered to be at ground level.
a) absolute zero
b) 0 o C
c) 100 o C
d) 100 K
Answer: a
Explanation: Each of the orbital electrons is associated with unique energy levels. At absolute zero temperature an atom is considered to be at ground level when all the electrons occupy their respective lowest potential energy.
9. The electrons at ground state can be excited to a higher state of energy by _____
a) increasing the pressure
b) lowering the energy
c) absorbing the energy
d) oxidising the atom
Answer: c
Explanation: The electrons at ground state can be excited to higher state of energy by absorbing energy form external sources like increase in electronic vibration at elevated temperature, through chemical reaction as well as via absorbing the energy of the photon.
10. The geometry and radii of orbital paths of electrons depend on the presence of an electromagnetic field.
a) True
b) False
Answer: a
Explanation: In the model of an atom, negatively charged electrons rotate around the positively charged nucleus in some specified orbital paths. The geometry and radii of such orbital paths depend on a variety of parameters like number of electrons, presence of neighbouring atoms and their electron structure, presence of an electromagnetic field, etc.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Beam Machining – 2”.
1. When coming back to normal state from excited state, electron releases _____
a) proton
b) anti-proton
c) positron
d) photon
Answer: d
Explanation: On reaching the higher energy level, the electron reaches an unstable energy band. And it comes back to its ground state within a very small time by releasing a photon. This is called spontaneous emission.
2. In population inversion, no of electrons in _____ are more as compared to numbers of electrons in _____
a) quasi-stable state, ground state
b) meta-stable state, ground state
c) meta-stable state, quasi-stable state
d) mono-stable state, ground state
Answer: b
Explanation: Sometimes such change of energy state puts the electrons in a meta-stable energy band. Instead of coming back to its ground state immediately it stays at the elevated energy state for micro to milliseconds. In a material, if more number of electrons can be somehow pumped to the higher meta-stable energy state as compared to the number of atoms at ground state, then it is called “population inversion”.
3. In laser beam machine, one end of the glass is_____
a) open
b) blocked with a 10% reflective mirror
c) blocked with a 75% reflective mirror
d) blocked with a 100% reflective mirror
Answer: d
Explanation: The gas, called lasing medium is enclosed in a cylindrical glass vessel. One end of the glass is blocked with a 100% reflective mirror and the other end is having a partially reflective mirror.
4. In laser beam machining, electrons are excited by _____
a) high temperature steam
b) flash lamps
c) flash torch
d) cathode ray tube
Answer: b
Explanation: Population inversion can be carried out by exciting the gas atoms or molecules by pumping it with flash lamps. Then stimulated emission would initiate lasing action. Stimulated emission of photons could be in all directions.
5. The photons emitted in the _____ direction form a laser beam.
a) vertical
b) horizontal
c) longitudinal
d) lateral
Answer: c
Explanation: Most of the stimulated photons, not along the longitudinal direction would be lost and generate waste heat. The photons in the longitudinal direction would form coherent, highly directional, intense laser beam.
6. How many types of lasers are there?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: Many materials can be used as the heart of the laser. Depending on the lasing medium lasers are classified as:
• Solid-state laser
• Gas laser.
7. How many types of solid state lasers are there?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: Solid-state lasers are commonly of the following type:
• Ruby which is a chromium – alumina alloy having a wavelength of 0.7 μm
• Nd-glass lasers having a wavelength of 1.64 μm
• Nd-YAG laser having a wavelength of 1.06 μm
These solid-state lasers are generally used in material processing.
8. Lasers can be operated in _____ modes
a) 2
b) 7
c) 8
d) only one
Answer: a
Explanation: Lasers can be operated in
• continuous mode, or
• pulsed mode
Typically CO 2 gas laser is operated in continuous mode and Nd – YAG laser is operated in pulsed mode.
9. Helium-Neon is a gas laser.
a) True
b) False
Answer: a
Explanation: The generally used gas lasers are:
• Helium – Neon
• Argon
• CO 2 etc.
10. Flash tubes used for Nd-YAG laser can be helical or flat.
a) True
b) False
Answer: a
Explanation: Nd-YAG laser is pumped using a flash tube. Flash tubes can be helical, or they can be flat. Typically the lasing material is at the focal plane of the flash tube. Though helical flash tubes provide better pumping, they are difficult to maintain.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Beam Machining – 3”.
1. The flash tube is operated in _____ mode.
a) pulsed
b) continuous
c) reversed
d) synchronous
Answer: a
Explanation: The flash tube is operated in pulsed mode by charging and discharging of the capacitor. Thus the pulse on time is decided by the resistance on the flash tube side and pulse off time is decided by the charging resistance. There is also a high voltage switching supply for initiation of pulses.
2. How many types of flows are possible in gas lasers?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: Gas lasers can be:
• Axial flow
• Transverse flow
• Folded flow.
3. The power of CO 2 laser is around______
a) 15 Watt per meter of tube length
b) 55 Watt per meter of tube length
c) 100 Watt per meter of tube length
d) 1 MW per meter of tube length
Answer: c
Explanation: The power of a CO 2 laser is typically around 100 Watt per metre of tube length. Thus to make a high power laser, a rather long tube is required which is quite inconvenient. For optimal use of floor space, high-powered CO 2 lasers are made of folded design.
4. In a CO 2 laser, a mixture of _____ is circulated through the gas tube.
a) CO 2 , N 2 and He
b) CO 2 , N 2 and Ar
c) CO 2 , H 2 and N 2
d) CO 2 , I 2 and O 2
Answer: a
Explanation: In a CO 2 laser, a mixture of CO 2 , N 2 and He continuously circulate through the gas tube. Such continuous recirculation of gas is done to minimize consumption of gases.
5. In CO 2 laser, ‘He’ gas is used for cooling purpose.
a) True
b) False
Answer: a
Explanation: CO 2 acts as the main lasing medium whereas nitrogen helps in sustaining the gas plasma. Helium on the other hand helps in cooling the gases. High voltage is applied at the two ends of the tube leading to discharge and formation of gas plasma.
6. CO 2 lasers are folded to achieve _____________
a) high power
b) high depth of cuts
c) high material removal rate
d) avoid over heating
Answer: a
Explanation: CO 2 lasers are folded to achieve high power. In folded laser, there would be a few 100% reflective turning mirrors for manoeuvring the laser beam from the gas supply as well as a high voltage supply.
7. Nd-YAG laser can be used for drilling holes in the range of _____ diameter.
a) 0.25 mm – 1.5 mm
b) 1 mm – 1.5 mm
c) 1.5 mm – 2 mm
d) 2 mm – 2.5 mm
Answer: a
Explanation: For drilling holes as small as 0.25mm and as large as 1.5mm diameter, following lasers are used;
• Nd-YAG,
• Nd-glass, and
• Ruby.
8. For which of the following materials CO 2 laser is not used?
a) Plastics
b) Metals
c) Organic materials
d) Ceramics
Answer: b
Explanation: For,
• Plastics— CO 2 laser is used
• Metals—Nd-YAG, Ruby, Nd-glass lasers are used
• Organic materials and non-metals—Pulsed CO 2 laser is used
• Ceramics—Pulsed CO 2 , Nd-YAG lasers are used.
9. Which of the following does not hold true about laser beam machining?
a) High initial cost
b) High running cost
c) No heat affected zone
d) It is not suitable for heat sensitive materials
Answer: c
Explanation: Following are the limitations of laser beam machining;
• High initial capital cost
• High maintenance cost
• Not very efficient process
• Presence of Heat Affected Zone – specially in gas assist CO 2 laser cutting
• Thermal process – not suitable for heat sensitive materials like aluminium glass fibre laminate.
10. Using lasers, large aspect ratio in drilling can be achieved.
a) True
b) False
Answer: a
Explanation: Following are the advantages of laser beam machining:
• In laser machining, there is no physical tool. Thus no machining force or wear of the tool takes place.
• Large aspect ratio in laser drilling can be achieved along with acceptable accuracy or dimension, form or location
• Micro-holes can be drilled in difficult – to – machine materials
• Though laser processing is a thermal processing but heat affected zone especially in pulse laser processing is not very significant due to the shorter pulse duration.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Wire-cut EDM – 1”.
1. A thin metallic wire used in wire-cut EDM is kept submerged in a tank of _____
a) dielectric fluid
b) pure water
c) molten metal
d) kerosene
Answer: a
Explanation: The Wire Electric Discharge Machining is a variation of EDM and is commonly known as wire-cut EDM or wire cutting. In this process, a thin metallic wire is fed onto the workpiece, which is submerged in a tank of dielectric fluid such as deionized water.
2. Wire-cut EDM can cut plates of thickness upto _____
a) 50mm
b) 100mm
c) 300mm
d) 500mm
Answer: c
Explanation: Wire-cut EDM process can cut plates as thick as 300mm and is used for making punches, tools and dies from hard metals that are difficult to machine with other methods.
3. In WEDM, the wire is held tight between_____
a) upper and lower nozzles
b) upper and lower diamond guides
c) upper and lower groves in the handle
d) upper and lower pulleys
Answer: b
Explanation: In wire-cut EDM , the wire which is constantly fed from a spool, is held between upper and lower diamond guides. The guides are usually CNC-controlled and move in the x–y plane.
4. The upper guide can move independently about_____
a) x-axis
b) y-axis
c) x-y-w axes
d) z-u-v axes
Answer: d
Explanation: On most machines, the upper guide can move independently about the z–u–v axes, giving it the flexibility to cut tapered and transitioning shapes .
5. In the wire-cut EDM process, de-ionizing units are used for controlling the _____
a) feed rate
b) resistivity
c) burr formation
d) temperature of the wire
Answer: b
Explanation: In the wire-cut EDM process, water is commonly used as the dielectric fluid. Filters and de-ionizing units are used for controlling the resistivity and other electrical properties.
6. In the wire-cut EDM process, water is also used for _____
a) cooling
b) increasing the feed rate
c) flushing away the burr
d) controlling the cutting speed
Answer: c
Explanation: Apart from being used as a dielectric fluid, the water also helps in flushing away the debris from the cutting zone. The flushing also helps to determine the feed rates to be given for different thickness of the materials.
7. The WEDM process requires _____
a) lower initial investment
b) lesser cutting forces
c) a skilled operator
d) a coolant pump
Answer: b
Explanation: The wire-cut EDM process requires lesser cutting forces in material removal; hence it is generally used when lower residual stresses in the workpiece are desired.
8. The materials which are not stress-relieved before machining by WEDM process can get distorted during machining.
a) True
b) False
Answer: a
Explanation: If the energy/power pulse is relatively low , little changes in the mechanical properties of the material are expected due to residual stresses. The components which are not stress-relieved earlier can get distorted in the machining process.
9. During the WEDM process, workpiece undergoes a number of thermal cycles.
a) True
b) False
Answer: a
Explanation: In WEDM process, the selection of process parameters is very crucial, as in some cases the workpiece undergoes significant thermal cycles the can be very severe. These thermal cycles can form recast layers and induce residual tensile stresses on the workpiece.
10. Electrically conductive materials are cut by WEDM process by _____ mechanism.
a) thermal
b) electro-thermal
c) electro-dynamic
d) fused metal
Answer: b
Explanation: Electrically conductive materials are cut by WEDM process by an electro-thermal mechanism. In the WEDM process, the motion of the wire is slow. It is fed in the programmed path and material is removed from the workpiece accordingly.
This set of Manufacturing Processes Problems focuses on “Wire-cut EDM – 2”.
1. In wire-cut EDM process, material removal takes place by a series of discrete discharges between _____
a) di-electric fluid and the wire electrode
b) the wire-electrode and the workpiece
c) the workpiece and the CNC-table
d) wire electrodes
Answer: b
Explanation: In wire-cut EDM process, material removal takes place by a series of discrete discharges between the wire and the workpiece in the presence of a di-electric fluid. Water is commonly used as the di-electric fluid.
2. The di-electric fluid gets ionizes in between _____ gap.
a) tool-electrode
b) cathode-anode
c) workpiece-electrode
d) tool-workpiece
Answer: a
Explanation: The di-electric fluid gets ionized in between the tool-electrode gap and hence, helps in creating a path for each discharge. Because of these discharges, material is removed from the workpiece.
3. The burr or cut particles are flushed away by the______
a) electrode
b) motion of the workpiece
c) di-electric fluid
d) coolant
Answer: c
Explanation: The area wherein discharge takes place gets heated to very high temperatures such that the surface gets melted and removed. The cut particles get flushed away by the continuously flowing dielectric fluid.
4. Wire-cut EDM process is widely used for _____
a) alloy steels
b) tool steels
c) stainless steels
d) carbon steels
Answer: b
Explanation: WEDM is a non-conventional process and is very widely used in tool steels for a pattern and die making industries. The process is also used for cutting intricate shapes in components used for the electric and aerospace industries.
5. For which of the following materials wire-cut EDM is not used?
a) Aluminium
b) Zirconium
c) Steels
d) Titanium
Answer: b
Explanation: Wire-cut EDM is used for cutting:
• Aluminium
• Brass
• Copper
• Graphite
• Steels
• Titanium.
6. WEDM process can be used for cutting hard extrusion dies.
a) True
b) False
Answer: a
Explanation: This process is used in the following areas:
• Aerospace, Medical, Electronics and Semiconductor applications
• Tool & Die making industries.
• For cutting the hard Extrusion Dies
• In making Fixtures, Gauges & Cams.
7. WEDM process can be used for manufacturing of micro-tools.
a) True
b) False
Answer: a
Explanation: Following are the few areas where WEDM process is used:
• Cutting of Gears, Strippers, Punches and Dies
• Manufacturing hard Electrodes
• Manufacturing micro-tooling for Micro-EDM, Micro-USM and such other micromachining applications.
8. How many subsystems are there in wire-cut EDM process?
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: The subsystems of Wire-EDM process are:
• Power supply
• Di-electric system
• Wire feeding system
• Positioning system.
9. Di-electric system used in WEDM process is similar to that of the _____ process.
a) conventional drilling
b) conventional milling
c) conventional EDM
d) broaching
Answer: c
Explanation: The power supply and the di-electric system used in WEDM is very similar to that of the conventional EDM. The main difference lies only in the type of di-electric used.
10. In wire-cut EDM, a moving wire is used to _____
a) remove the burr
b) cut complex outlines
c) melt the material
d) make the way for the di-electric fluid
Answer: b
Explanation: In wire-cut EDM, a moving wire is used to cut complex outlines and fine details in the required workpiece. The wire is wound on a spool and is kept in constant tension.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Wire-cut EDM – 3”.
1. Wire electric discharge machining is based on the same principle as that of _____
a) hydro-dynamic EDM
b) die-sink EDM
c) polar EDM
d) non-conventional EDM
Answer: b
Explanation: Wire electric discharge machining is based on the same principle as die-sink ED machining. The basic elements in all EDM methods are dielectric fluid, a workpiece and an electrode.
2. The only difference between die-sink EDM and wire cut EDM is the _____
a) way of material removal
b) electrode used for the machining
c) type of materials machined
d) processing time
Answer: b
Explanation: In the die-sink EDM method the electrode has the same shapes as the wished machining results. In the wire cut EDM method the electrode is a moving wire made from some electrically conducting material. The workpiece is cut with the electrode wire.
3. During wire cut EDM, the size of the cavity produced by the wire while machining depends upon _____
a) material of the workpiece
b) di-electric fluid used
c) wire material
d) electric current
Answer: d
Explanation: While machining a high electric current passes through the dielectric fluid and heats the workpiece surface from a very small area. The corresponding workpiece area melts and what is left, is a small round cavity. The cavity size depends on the electric current and potential.
4. Sparking gap is the distance between _____
a) the workpiece and the CNC table
b) the workpiece and the electrode wire
c) the electrode wire and the di-electric fluid
d) the workpiece and the spark plug
Answer: b
Explanation: The distance between the electrode wire and the workpiece is called a sparking gap. The electrode produces shapes that are a sparking gap dimension larger than the programmed shape through which the electrode wire passes.
5. The absolute minimum inner corner radius is _____
a) the wire radius minus the sparking gap width
b) the sparking gap width minus the wire radius
c) the wire radius plus the sparking gap width
d) double of the wire radius
Answer: c
Explanation: The absolute minimum inner corner radius is the wire radius added with the sparking gap width. Therefore during machining, the shapes produced have larger dimensions as compared to the shapes mentioned in the program.
6. The wire ED machines have _____ programmable axes.
a) 2
b) 2-5
c) 6
d) 3-9
Answer: b
Explanation: The wire cut EDM machines have 2 – 5 programmable axes. The machines that are used in mould making applications typically have 5 programmable axes. These axes are Wire guide, wire tilting in x and y –directions and workpiece or wire system movements in x and y –directions.
7. Which of the following component of the wire cut EDM machine does not get heated?
a) Workpiece
b) Electrode wire
c) Di-electric fluid
d) Coils
Answer: b
Explanation: The electrode wire moves between two coils with a moderate speed. The part of the wire that actually machines the workpiece is constantly changing. There is no time for the wire to heat up.
8. Which of the following material properties sets restrictions to use wire cut EDM?
a) Material type
b) Melting point
c) Material hardness
d) Electrical conductivity
Answer: d
Explanation: As the electrode wire does not get heated during machining, the problems with electrode wear are not an issue like in the case of die-sink ED machining and it is possible to use wire cut EDM also for materials with high melting ranges. The material hardness sets no restrictions. The only restriction is that the material needs to be electrically conductive.
9. Wires used in wire cut EDM are usually disposed after one usage.
a) True
b) False
Answer: a
Explanation: Despite the minimum wear, wires are usually disposed after one usage. Sparking and high temperature during the machining reduces the wire tensile strength and the wire could easily break if re-used.
10. The electrode wires are usually made form _____
a) graphite
b) iron
c) nickel
d) brass
Answer: d
Explanation: Wire used in wire cut EDM are usually made of brass – either zinc-coated or uncoated. Brass wire can be purchased in different hardnesses and different diameters. Zinc coated wire is used in machining high melting point workpiece materials.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Wire-cut EDM – 4”.
1. _____ grades wire are used in automatic re-threading mechanisms.
a) Malleable
b) Softer
c) Harder
d) Commercial
Answer: c
Explanation: The harder grades are used in automatic re-threading mechanisms and also if the machined shapes contain high flat surfaces. Hard wires resist change in direction and for that reason are likely to produce nice flat surfaces.
2. For machining of high melting point materials, _____ wires are used.
a) gallium
b) zinc coated
c) aluminium coated
d) silver
Answer: b
Explanation: Zinc coated wire is used in machining high melting point workpiece materials. The zinc coating vaporises in lower temperature than the brass core. Vaporisation reduces the amount of heat that transmits to the brass and the core wears less.
3. _____ is/are used as di-electric fluid in die sink EDM process.
a) Pure water
b) Silicone gel
c) Petroleum products
d) Epoxy resins
Answer: c
Explanation: The dielectric fluid in the die-sink EDM process is usually some petroleum product. In the wire cut EDM process, it is most common to use de-ionised water.
4. Which of the following is not the application of wire cut EDM process?
a) Machining ejector holes
b) Cutting the ejector pins
c) Machining cores of various moulds
d) Machining of complex shapes made of plastic
Answer: d
Explanation: The most typical wire cut EDM applications in mould making are: −
• Machining ejector holes
• Shaping and cutting the ejector pin ends to follow mould cavity surface shapes
• Machining cores and corresponding fastening holes in the mould plates and inserts.
5. During mould making by wire cut EDM, it is important to harden ______ to counter the effects of changes in the shape of the workpiece due to heat treatment.
a) the insert
b) electrode wire
c) electrode holding coils
d) bolting points in the workpiece
Answer: a
Explanation: It is important to harden the insert or mould plate steel before making the tightly tolerated ends in the ejector pin holes because the heat treatment tends to change the workpiece shapes at a certain degree.
6. Which of the following machining process is usually preferred for cutting of ejectors which are used in mould making?
a) Milling
b) Hobbing
c) Wire-cut EDM
d) Die sink EDM
Answer: c
Explanation: There is a need to cut the ejector to a right dimension and if the cavity surface is shaped there is also a need to shape the ejector end. The wire ED machine is one of the most accurate machines in mould shops and usually there is also free machining time available. Another option is to cut and shape the ejectors in a milling machine, but the most accurate milling machines are used in mould cavity machining operations and normally they are rather busy for long periods of time.
7. How many ways are there for making the fixed cores by wire cut EDM process?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: Basically there are two options for making the fixed cores:
− Machine the cores directly to the mould insert plate or mould plate
− Machine the cores to separate pieces of mould steel and attach the piece to the mould assembly.
8. The selection of the manufacturing process depends upon ____________
a) chemical reactivity between the mould material and the di-electric fluid
b) mould shape
c) application of the mould
d) number of parts to be machined
Answer: b
Explanation: The selection depends on the core dimensions and shapes. High and narrow cores or cores with sharp shapes are easiest to manufacture with separate parts. Special cases are core pins. Core pins are used in making small diameter holes to castings.
9. The wire EDM process is used for making moulds with high drafted walls.
a) True
b) False
Answer: a
Explanation: Like every wall in the mould opening direction, the core walls are also drafted. It is rather difficult to make high drafted walls with a milling machine. Especially in the case of injection moulding or high pressure die casting moulds where the accuracy requirements are very high. The wire ED machine produces these shapes accurately with ease.
10. For manufacturing of complex shapes, soft electrode wires are used.
a) True
b) False
Answer: a
Explanation: Soft wires are useful in applications with complex shapes, where the machine changes the wire tilting angle several times. The harder grades are used in automatic re-threading mechanisms.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Wire-cut EDM – 5”.
1. Which of the following materials is not machined by wire cut EDM?
a) Inconel
b) Graphite
c) Tool steel
d) Hastaloy
Answer: d
Explanation: It can machine anything that is electrically conductive, from relatively common materials such as tool steel, aluminium, copper, and graphite, to exotic space-age alloys including hastaloy, waspaloy, inconel, titanium, carbide, polycrystalline diamond compacts and conductive ceramics.
2. Which of the following does not hold true about wire cut EDM?
a) The electrode wire touches the workpiece while cutting the workpiece material
b) It can machine any electrically conductive material irrespective of its hardness
c) The di-electric fluid gets ionized in between the tool-electrode gap
d) During machining, the electrode wire does not get heated
Answer: a
Explanation: The wire does not touch the workpiece, so there is no physical pressure imparted on the workpiece compared to grinding wheels and milling cutters.
3. Which of the following is true about wire cut EDM?
a) Minimal clamping forces are required to hold the workpieces
b) It is a conventional process
c) It can machine materials like fibres, plastics, wood, etc
d) Electrodes used in die sink EDM and wire cut EDM are same
Answer: a
Explanation: The amount of clamping pressure required to hold small, thin and fragile parts is minimal, preventing damage or distortion to the workpiece.
4. Which of the following is true about wire cut EDM?
a) It leaves no residual burrs
b) It cannot machine materials having hardness beyond 20 BHN
c) It has poor accuracy as compared to milling
d) It uses petroleum products as di-electric fluid
Answer: a
Explanation: The EDM process leaves no residual burrs on the workpiece, which reduces or eliminates the need for subsequent finishing operations which indeed reduces the overall machining cost.
5. Large scale wire cut EDM machines can handle workpieces weighing upto _____ pounds.
a) 100
b) 600
c) 1000
d) 10000
Answer: d
Explanation: Wire cut EDM machines are manufactured in various sizes and styles of flush or submerged type machines to fit the needs of the consumer. Large scale machines can handle workpieces weighing over ten thousand pounds and can cut over twenty inches thick.
6. Wire cut EDM process can cut tapers of _____ degrees.
a) 5-10
b) 8-16
c) 20-30
d) 25-45
Answer: c
Explanation: In addition to the X-Y table travels, wire EDM’s have U / V travels for providing the movement to cut tapers. Most machines can cut tapers of 20-30 degrees depending on workpiece thickness.
7. Wire cut EDM machines work on _____ current.
a) direct
b) alternating
c) both direct and alternating
d) eddy
Answer: c
Explanation: In wire EDM, the conductive materials are machined with a series of electrical discharges that are produced between an accurately positioned moving wire and the workpiece. High frequency pulses of alternating or direct current are discharged from the wire to the workpiece with a very small spark gap through an insulated dielectric fluid.
8. The heat of each electrical spark generated during machining is around_____ Fahrenheit
a) 1,000° to 2,000°
b) 1,100° to 5,000°
c) 10,000° to 12,000°
d) 15,000° to 21,000°
Answer: d
Explanation: The heat of each electrical spark, estimated at around 15,000° to 21,000° Fahrenheit, which erodes away a tiny bit of material that is vaporized and melted from the workpiece.
9. The de-ionised water is used for flush away the burr as well as to cool the workpiece.
a) True
b) False
Answer: a
Explanation: The particles generated during machining are flushed away from the cut with a stream of de-ionized water through the top and bottom flushing nozzles. The water also prevents heat build-up in the workpiece. Without this cooling, thermal expansion of the part would affect the size and positional accuracy.
10. In wire cut EDM, machine movement is accomplished with precision lead screws with recirculating ball bearings.
a) True
b) False
Answer: a
Explanation: Machine movement is accomplished with precision lead screws with recirculating ball bearings on all axes that are driven by AC motors. Before shipping, the machine’s position is checked and any errors or backlash are corrected by pitch error compensation that is permanently stored in the computer’s memory.
This set of Basic Manufacturing Processes Questions and Answers focuses on “Wire-cut EDM – 6”.
1. Copper is not used for making electrode wires in wire cut EDM because of its _____
a) Good conductivity
b) lower tensile strength
c) high melting point
d) higher purchasing cost
Answer: b
Explanation: The low tensile strength of copper wire made it subject to wire breaks when too much tension was applied. Poor flushability was another problem, due to coppers high thermal conductivity. A good portion of the heat from the EDM spark was transferred to the wire and carried away from the workzone instead of using that heat to melt and vaporize the workpiece.
2. Which of the following materials is not used for electrode wires?
a) Molybdenum
b) Brass
c) Steel
d) Graphite
Answer: c
Explanation: There is a vast array of wires to choose from with brass wire normally being used however, molybdenum, graphitized, and thick and thin layered composite wires are available for different applications.
3. Selection of the wire is based on how many factors?
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: The selection of wires is dependent on the following factors:
• Cutting speeds
• Taper angles to be machined
• Tensile strength
• Flushability.
4. The diameter of the electrode wire is in the range of _____
a) 0.001″ – 0.0035″
b) 0.003″ – 0.004″
c) 0.004″ – 0.014″
d) 0.020″ – 0.032″
Answer: c
Explanation: Wire diameters range from .004″ through .014″ with .010″ being the most commonly used. The wire originates from a supply spool, then passes through a tension device . It then comes in contact with power feed contacts where the electric current is applied.
5. After originating from a supply spool, the wire is passed through _____
a) a chamber filled with special stones
b) diamond guides
c) a furnace
d) a container filled with anti-oxidant
Answer: b
Explanation: After originating from a supply spool, the wire then passes through a set of precision, round diamond guides, and is then transported into a waste bin. The wire can only be used once, due to it being eroded from the EDM process.
6. With the addition of the programmable _____ to wire cut EDM machine, workpieces of different thicknesses can be machined.
a) X-axis
b) Y-axis
c) Z-axis
d) chuck
Answer: c
Explanation: With the addition of the programmable “Z” axis, workpieces of different thickness, can also be machined. For example, the die openings and dowel pin holes can be machined on a one inch thick die block, then the machine can be programmed to move to another location and machine the punches on a two or three inch thick workpiece.
7. In a wire break situation, the end of the wire is_____ while the supply wire is _____
a) clamped, drawn back
b) drawn back, clamped
c) dipped in the di-electric fluid, clamped
d) welded with the other wire, drawn back
Answer: a
Explanation: The threading process of the automatic wire threader takes place automatically if there is a broken wire or by a command in the program. In a wire break situation, the end of the wire is clamped while the supply wire is drawn back, annealing and separating the wire, while leaving a sharp point on the end of the supply wire.
8. The automatic wire threading offers the ability to cut multiple openings in a workpiece without operator intervention.
a) True
b) False
Answer: a
Explanation: This feature allows multiple openings to be cut in die blocks, progressive dies, production, and prototype workpieces automatically and unattended without the intervention of an operator, resulting in higher productivity. The demand for automatic wire threading and dependent reliability has been met with new and improved designs.
9. If there is a wire break during machining, the machine returns to the start point.
a) True
b) False
Answer: a
Explanation: If there is a
wire break during machining, the machine returns to the start point of that opening, re-threads the wire and move through the program path to the position where it broke, powers up, and continues cutting as if the wire had never broken.
10. After a wire break, the wire tip segment that was clamped is disposed off in a wire tip disposal unit.
a) True
b) False
Answer: a
Explanation: The wire tip segment that was clamped is disposed of in a wire tip disposal unit. The supply wire is then directed into the lower guide. The wire then proceeds to the back of the machine where it is discarded in a scrap wire bin.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Wire-cut EDM – 7”.
1. In wire cut EDM machine, _______ axes are positioned away from the work area to avoid moisture and contamination.
a) X and Y
b) X and Z
c) U and V
d) Y and V
Answer: c
Explanation: The rigid U and V axis is positioned away from the work area to avoid moisture, contamination and deflection from the high pressure flush. Most Wire EDM’s are equipped with a programmable “Z” axis giving precise control of the upper guide assembly to ensure accurate tapers.
2. The U and V axes provide movement to the wire to produce taper angles upto _____ degrees.
a) 15
b) +/- 20
c) +/- 30
d) 45
Answer: c
Explanation: These axes provide movement to the top portion of the wire to produce taper angles of up to +/- 30 degrees. Both conical and oblique cylindrical radii can be programmed, and the size of the top and bottom radii of the part can also be programmed.
3. During the wire cut EDM process, the feature of adjustable tapering values is useful for _____
a) circular workpieces
b) mould applications
c) thick workpieces
d) forging dies
Answer: b
Explanation: Tapering values can be changed within the program. This is useful for mold applications or form tools that have different side and frontal taper relief angles. Die blocks are normally machined first with their taper relief, then straight cut for their die land.
4. The function of independent programming of the U & V axes in wire cut EDM machines is for _______
a) hexagonal workpieces
b) fullerene shaped workpieces
c) workpieces having a different shape on the top and bottom
d) workpieces having intricate shapes
Answer: c
Explanation: Wire cut EDM machines have U / V travels for providing the movement to cut tapers. Independent programming of the U & V axes is for workpieces that have a different shape on the top and bottom.
5. Which of the following is not machined by wire cut EDM?
a) airfoils
b) extrusion dies
c) square shaped objects
d) perforated sheets
Answer: d
Explanation: The independent, simultaneous movement of all four axes makes machining extrusion dies, airfoil shapes, and “squircles” quite easy.
6. How many sections does the di-electric system includes?
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: The dielectric system includes:
• the water reservoir
• filtration system
• de-ionization system
• water chiller unit.
7. While machining, the dirty water is filtered through a _____
a) paper filter
b) notch filters
c) comb filters
d) fir filters
Answer: a
Explanation: During cutting, the dirty water is drained into the unfiltered side of the dielectric reservoir where the water is then pumped and filtered through a paper filter, and returned to the clean side of the dielectric tank.
8. In a wire cut EDM machine, _____ is used to control the resistivity of the de-electric fluid .
a) resin beds
b) water reservoir
c) de-ionisation system
d) diamond guides
Answer: a
Explanation: Following filtration, the clean water is measured for conductivity, and if required passes through a vessel that contains a mixed bed of anion and cation beads. This mixed bed resin controls the resistivity of the water to set values automatically.
9. A water chiller is used to keep _____ thermally stable.
a) electrode wire
b) electrode coils
c) control arms
d) dielectric reservoir
Answer: c
Explanation: A water chiller is provided as standard equipment to keep following systems thermally stable:
• the dielectric
• workpiece
• worktable
• control arms
• fixtures.
10. During the cutting process water conductivity level changes due to eroded chips.
a) True
b) False
Answer: a
Explanation: During the cutting process the chips from the material that is being eroded, gradually changes the water conductivity level. Resistivity levels of the water are set according to the cutting requirements of the workpiece material being machined.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Wire-cut EDM – 8”.
1. Submerged machining is extremely useful for applications that generally have_____
a) poor flushing conditions
b) intricate shapes
c) tapered sections
d) good weldability
Answer: a
Explanation: Submerged machining is extremely useful for applications that generally have poor flushing conditions. Applications where poor flushing conditions exist are numerous.
2. Submerged machining is used for ____
a) cutting small taper angles
b) tiny workpieces
c) laminations
d) workpieces with no undercuts
Answer: c
Explanation: Some applications and examples where submerged machining is more practical would be cutting large taper angles, tall workpieces, laminations, tubes, irregular shaped parts, workpieces with undercuts and cutting very close to the edge of the workpiece.
3. There is a greater risk of breaking a wire if ______
a) temperature of the wire is too high
b) larger taper angles are to be cut
c) the flush is not set properly
d) there is an inadequate flow of di-electric fluid
Answer: c
Explanation: There is a greater risk of breaking a wire if the flush is not set properly or if too much power is used. This condition is greatly reduced when cutting the part submerged.
4. How many of the following processes does not need submerged machining capabilities?
– starting a cut from the edge of a workpiece
-slicing a tube
-slicing a bar stock
-starting a cut from a large diameter start hole.
a) 1
b) 2
c) 3
d) 4
Answer: d
Explanation: When starting a cut from the edge of a workpiece, cutting a form tool, slicing a tube or bar stock, or starting a cut from a large diameter start hole, is a slower process without submerged machining capabilities.
5. When parts with existing openings in them must be cut, conventional flushing produces _____
a) air pockets
b) unnecessary tapers
c) undercuts
d) poor flushing
Answer: a
Explanation: When parts with existing openings, slots or cross holes in them must be cut, conventional flushing produces air pockets and results in reduced performance or wire breaks. Submerged machining provides stable cutting of these parts.
6. When it is not possible to have the flushing nozzles close to the top or bottom of the workpiece _____ machines may require constant adjustment of the top and bottom flush.
a) submerged type
b) splash flush
c) rigid flush
d) stock flush
Answer: b
Explanation: When it is not possible to have the flushing nozzles close to the top or bottom of the workpiece, splash flush machines may require constant adjustment of the top and bottom flush. When machining submerged, you can adjust the flush once and forget it.
7. Which of the following is not the benefit of submerged cutting?
a) improved accuracy
b) better surface finish
c) Thermal stability
d) no wire breakage
Answer: d
Explanation: Benefits of submerged cutting are:
• Enhanced thermal stability of the entire set up
• Accurate skim cuts
• Better surface finish
• Improved accuracy.
8. Submerged cutting helps cutting the workpieces without hampering the flush.
a) True
b) False
Answer: a
Explanation: Cutting round stock or tubing presents a combination of adverse effects. Submerged cutting can efficiently cut these jobs without the flush being impaired.
9. Which of the following is not the effect of less maintenance of the wire cut EDM machines?
a) Wire breaks
b) Lines in the part
c) Lowered time to complete the job
d) Rough surfaces
Answer: c
Explanation: the lack of maintenance will lead to slower cutting speeds, size inaccuracy, lines in the part, wire breaks, a rougher surface finish, and a service call. Maintenance of Wire EDM machine usually consumes twenty to thirty minutes a week or less.
10. In how many of the following applications, wire cut EDM can be used?
– Manufacturing of progressive, blanking and trim dies
– Extrusion dies
– Cutting difficult to machine materials like hastaloy, inconel and titanium
– Cutting narrow slots and keyways
– Manufacturing of parts where burrs can’t be tolerated.
a) 1
b) 3
c) 4
d) 5
Answer: d
Explanation: Wire cut EDM has a broad range of applications that are continuing to grow. Some of them are listed below:
. Parts with complex geometry’s
. Parts requiring “tenths” tolerances
. Parts where burrs can’t be tolerated
. Thin or delicate parts that are susceptible to tool pressure
. Progressive, blanking and trim dies
. Extrusion dies
Precious metals
. Narrow slots and keyways
. Mold components
. Tooling for forging, or injection molding operations.
. Medical and dental instrumentation
. Cutting hardened materials such as carbide, C.B.N. and P.C.D.
Cutting difficult to machine materials like hastaloy, inconel and titanium
. Aerospace, defense and electronic parts
. Prototypes parts
Production parts
Form tools and inserts
Electrodes for vertical EDM.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Welding – 1”.
1. Laser beam welding is a ______ joining process.
a) fission
b) fusion
c) coherent
d) plastic
Answer: b
Explanation: Laser is an acronym for light amplification by stimulated emission of radiation. Laser Beam Welding is a fusion joining process that produces coalescence of materials with the heat obtained from a concentrated beam of coherent, monochromatic light impinging on the joint to be welded.
2. Which of the following is used to direct laser beam?
a) glass apertures
b) perforated glass sheets
c) flat optical elements
d) electro-magnetic coils
Answer: c
Explanation: In the LBM process, the laser beam is directed by flat optical elements, such as mirrors and then focused to a small spot at the workpiece using either reflective focusing elements or lenses.
3. Inert gas shielding is generally employed to protect _____
a) laser beam
b) molten puddle of metal
c) filler electrode
d) lenses
Answer: b
Explanation: It is a non-contact process, requiring no pressure to be applied. Inert gas shielding is generally employed to prevent oxidation of the molten puddle and filler metals may be occasionally used.
4. Which of the following is a commercially used laser?
a) Nd-GAG laser
b) 1.06 µm wavelength CO 2 laser
c) 2 µm wavelength CO 2 laser
d) Nd- YAS laser
Answer: b
Explanation: The Lasers which are predominantly being used for industrial material processing and welding tasks are the Nd-YAG laser and 1.06 µm wavelength CO 2 laser, with the active elements most commonly employed in these two varieties of lasers being the neodymium ion and the CO 2 molecules respectively.
5. In solid state laser _____ is used as a dopant.
a) actinium ion
b) neodymium ion
c) platinum ion
d) lead ion
Answer: b
Explanation: It utilizes an impurity in a host material as the active medium. Thus, the neodymium ion is used as a ‘dopant’, or purposely added impurity in either a glass or YAG crystal and the 1.06 µm output wavelength is dictated by the neodymium ion.
6. The lasing material is a cylinder of a diameter of about _____ mm.
a) 5
b) 9
c) 17
d) 20
Answer: b
Explanation: The lasing material or the host is in the form of a cylinder of about 150 mm long and 9 mm in diameter. Both ends of the cylinder are made flat and parallel to each other.
7. The lasing material or crystal is excited by _____
a) neon lamps
b) krypton lamps
c) tungsten wire laps
d) CFLs
Answer: b
Explanation: Both ends of the cylinder are made flat and parallel to very close tolerances, then polished to a good optical finish and silvered to make a reflective surface. The crystal is excited by means of an intense krypton or xenon lamps.
8. Which of the following laser is the most efficient?
a) CO 2 lasers
b) Nd-YAG lasers
c) Ruby lasers
d) Dye lasers
Answer: a
Explanation: The electric discharge style CO 2 gas lasers are the most efficient type currently available for high power laser beam material processing. Dye lasers use complex organic dyes like rhodamine 6G.
9. CO 2 lasers employs gas mixture of _____
a) nitrogen and helium
b) hydrogen and helium
c) argon and xenon
d) oxygen and nitrogen
Answer: a
Explanation: These lasers employ gas mixtures primarily containing nitrogen and helium along with a small percentage of carbon dioxide, and an electric glow discharge is used to pump this laser medium.
10. Gas heating produced by gas lasers is controlled by _____
a) coolant
b) a blow of cool air
c) adjusting the wavelength of the laser
d) circulating the gas mixture
Answer: d
Explanation: Gas heating produced by gas lasers is controlled by continuously circulating the gas mixture through the optical cavity area and the thus CO2 lasers are usually categorized according to the type of gas flow in the system.
11. How many categorize are there of CO 2 lasers?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: CO 2 laser are usually categorized according to the type of gas flow in the type of gas flow in the system:
• slow axial
• fast axial
• transverse axial.
12. Slow axial flow gas lasers are simplest of the CO 2 lasers.
a) True
b) False
Answer: a
Explanation: They are the simplest of the CO 2 lasers. Gas flow in the same direction as the laser resonator’s optical axis and electric excitation field, or gas discharge path. These lasers are capable of generating laser beams with a continuous power rating.
13. Solid axial flow CO 2 lasers can generate laser beams with a constant rating of 80 Watts.
a) True
b) False
Answer: a
Explanation: These lasers can generate laser beams with a constant rating of approximately 80 Watts for every meter of discharge length. A folded tube configuration is used for achieving output power levels of 50 to 1000 Watts, maximum.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Welding – 2”.
1. ______ is used to circulate the laser gas in case of fast axial flow gas laser.
a) Compressor
b) Turbo pump
c) Guide vanes
d) Vane pump
Answer: b
Explanation: In the case of the FAF Laser, a roots blower or turbo pump is used to circulate the laser gas at high speed through the discharge region and corresponding heat exchangers.
2. Fast axial flow gas lasers are available between _____ watts power levels.
a) 10-100
b) 50-500
c) 500-6000
d) 6000-7000
Answer: c
Explanation: The fast axial flow lasers with continuous wave output power levels of between 500 to 6000 watts are available. The fast axial flow lasers have a similar arrangement of components as that of slow axial flow gas laser.
3. In transverse flow type gas lasers, gas is circulated across _____
a) the resonator cavity axis
b) optical axis
c) deflection coils
d) the focusing lens
Answer: a
Explanation: These lasers operate by continuously circulating gas across the resonator cavity axis by means of a high speed fan type blower while maintaining an electric discharge perpendicular to both the gas flow direction and the laser beam’s optical axis. Transverse flow lasers with output power levels between 1 and 25 kW are available.
4. In case of laser welding, heat input is _____ to fuse the weld metal.
a) equal to the required amount
b) close to the minimum required
c) greater by 200 J than required
d) approximately higher by atleast 320 J
Answer: b
Explanation: Following are the few advantages of Laser Beam Welding:
• Heat input is close to the minimum required to fuse the weld metal
• Reduced heat affected zones
• Workpiece distortions are minimized due to smaller heat affected zones.
5. Which of the following holds true about laser welding process?
a) Time for welding thick sections is more in case of LBW
b) Shielding gas is used to melt the burr formed during the machining
c) In LBW, sometimes filler metals are used
d) In Nd- YAG lasers, crystals of C14 are used as the lasing material
Answer: c
Explanation: Time for welding thick sections is reduced and the need for filler wires and elaborate joint preparations is eliminated by employing the single pass laser welding procedures but filler metals may be occasionally used.
6. Laser welding is performed with freedom from electrode contamination.
a) True
b) False
Answer: a
Explanation: In the case of laser beam welding, no electrodes are required; welding is performed with freedom from electrode contamination, indentation or damage from high resistance welding currents.
7. Which of the following does not hold true about laser beam welding?
a) Laser welding cannot be used in case of joints at intricate locations
b) It can produce tiny welds
c) Laser welding can be used for a variety of metal combinations
d) In case of LBW, thin welds on small diameter wires are less susceptible to burn back
Answer: a
Explanation: Following are the advantages of laser beam welding:
• Welding in areas that are not easily accessible with other means of welding can be done by LBM, since the beams can be focused, aligned and directed by optical elements
• Laser beam can be focused on a small area, permitting the joining of small, closely spaced components with tiny welds
• Wide variety of materials including various combinations can be welded
• Thin welds on small diameter wires are less susceptible to burn back than is the case with arc welding.
8. Laser welds are not influenced by _____
a) electric field
b) magnetic field
c) radio waves
d) ultraviolet rays
Answer: b
Explanation: Laser welds are not influenced by magnetic fields, as in arc and electron beam welds. They also tend to follow weld joint through to the root of the work-piece, even when the beam and joint are not perfectly aligned.
9. Aspect ratios, i.e., depth-to-width ratios of the order of _____ are attainable by LBW.
a) 1:2
b) 5:10
c) 10:1
d) 15:1
Answer: c
Explanation: Following are the few advantages of the LBW process:
• Aspect ratios of the order of 10:1 are attainable in LBM
• Metals with dissimilar physical properties, such as electric resistance can also be welded
• No vacuum or X-Ray shielding is required.
10. Weld penetrations of larger than _____ are difficult to weld by LBW.
a) 5 mm
b) 13 mm
c) 19 mm
d) 25 mm
Answer: c
Explanation: The maximum joint thickness that can be welded by a laser beam is somewhat limited. Thus weld penetrations of larger than 19 mms are difficult to weld. Also, joints must be accurately positioned laterally under the beam and at a controlled position with respect to the beam focal point.
11. Which of the following material properties has no effect on laser beam machining?
a) Reflectivity
b) Thermal conductivity
c) Weldability
d) Electrical conductivity
Answer: d
Explanation: High reflectivity and high thermal conductivity of materials like Al and Cu alloys can affect the weldability with lasers. Also, in case of mechanical clamping of the weld joints, it must be ensured that the final position of the joint is accurately aligned with the beam impingement point.
12. Lasers tend to have fairly low energy conversion efficiency.
a) True
b) False
Answer: a
Explanation: Following are the few limitations of the LBM Process:
• An appropriate plasma control device must be employed to ensure the weld reproducibility while performing moderate to high power laser welding
• Lasers tend to have fairly low energy conversion efficiency, generally less than 10 percent
• Some weld-porosity and brittleness can be expected, as a consequence of the rapid solidification characteristics of the LBM.
This set of Manufacturing Processes Question Paper focuses on “Laser Welding – 3”.
1. How many types of welding modes are there in laser beam welding?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: There are typically three types of welds:
– Conduction mode
– Conduction/penetration mode
– Penetration or keyhole mode.
2. Conduction mode welding is performed at _____ energy density.
a) high
b) medium
c) low
d) any
Answer: c
Explanation: Conduction mode welding is performed at low energy density forming a weld nugget that is shallow and wide. Conduction/penetration mode occurs at a medium energy density and shows more penetration than conduction mode.
3. The penetration or keyhole mode welding is characterized by ______
a) shallow welds
b) narrow welds
c) irregular welds
d) nuggets of welds
Answer: b
Explanation: The penetration or keyhole mode welding is characterized by deep narrow welds. This direct delivery of energy into the material does not rely on conduction to achieve penetration, and so minimizes the heat into the material and reduces the heat affected zone.
4. In penetration mode, a filament of vaporized material formed by laser light known as a _____
a) keyslot
b) keyhole
c) groove
d) burr
Answer: b
Explanation: In this mode, the laser light forms a filament of vaporized material know as a “keyhole” that extends into the material and provides conduit for the laser light to be efficiently delivered into the material.
5. In conduction welding, the laser beam is focused to a power density of order of _____ W/mm 2 .
a) 10 1
b) 10 2
c) 10 3
d) 10 4
Answer: d
Explanation: Conduction joining describes a family of processes in which the laser beam is focused:
– To give a power density on the order of 10 3 W/mm 2
– It fuses material to create a joint without significant vaporization.
6. Conduction welding has _____ modes.
a) single
b) 2
c) 3
d) 4
Answer: b
Explanation: Conduction welding has the following two modes:
– Direct heating
– Energy transmission.
7. The first conduction welds were made using _____ lasers.
a) Nd-YAG
b) ruby
c) polymer lasers
d) semiconductor lasers
Answer: b
Explanation: The first conduction welds were made in the early 1960s, using low power
• pulsed ruby lasers, and
• CO 2 lasers for wire connectors.
8. In direct heat conduction welding, heat flow is controlled by a conventional thermal conduction method.
a) True
b) False
Answer: a
Explanation: During direct heating, heat flow is governed by classical thermal conduction from a surface heat source and the weld is made by melting portions of the base material.
9. Conduction welds can be made in a wide range of metals and alloys in the form of wires and thin sheets.
a) True
b) False
Answer: a
Explanation: Conduction welds can be made in a wide range of metals and alloys in the form of wires and thin sheets in various configurations using
– CO 2 , Nd-YAG and diode lasers with power levels on the order of tens of watts
– Direct heating by a CO 2 laser beam can also be used for lap and butt welds in polymer sheets.
10. Transmission welding is used for joining _____
a) aluminium alloys
b) cast iron to wrought iron
c) polymers
d) components made of copper
Answer: c
Explanation: Transmission welding is an efficient means of joining polymers that transmit the near infrared radiation of Nd-YAG lasers and diode lasers.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Welding – 4”.
1. Which of the following material properties should match before joining to components by a transmission welding method.
a) Electrical properties
b) Thermal properties
c) Weldability
d) Tensile strength
Answer: b
Explanation: In transmission welding process, the energy is absorbed through novel interfacial absorption methods. Composites can be joined by this process provided that the thermal properties of the matrix and reinforcement are similar.
2. Transmission welding mode is used for materials that______
a) transmits near infrared radiation
b) have high heat capacities
c) have lower melting points
d) absorbs infrared radiations
Answer: a
Explanation: The energy transmission mode of conduction welding is used with materials that transmit near infrared radiation, notably polymer. Absorption of infrared radiation has nothing to do with weldability of materials.
3. In transmission welding mode, absorbing ink is placed at the interface of a lap joint for _____
a) absorbing the laser beam energy
b) cooling the work metal
c) protecting the weld puddle
d) reducing the process time
Answer: a
Explanation: An absorbing ink is placed at the interface of a lap joint. The ink absorbs the laser beam energy, which is conducted into a limited thickness of surrounding material to form a molten interfacial film that solidifies as the welded joint.
4. Butt welds can be made using transmission mode of conduction welding by _____
a) melting the outer surfaced of the joint
b) directing the energy towards the joint
c) applying ink to the joining surface before welding
d) using filler material
Answer: b
Explanation: Butt welds can be made by directing the energy towards the joint line at an angle through material at one side of the joint, or from one end if the material is highly transmissive. Also, thick section lap joints can be made without melting the outer surfaces of the joint.
5. In which of the following processes, the laser beam is used to melt a filler addition?
a) Laser drilling
b) Laser cutting
c) Laser welding
d) Laser soldering
Answer: d
Explanation: In the laser soldering and brazing processes, the beam is used to melt a filler addition, which wets the edges of the joint without melting the base material.
6. Penetration welding is characterised by _____
a) tapered trail
b) irregularities in the weld
c) parallel sided fusion zone
d) planner welds
Answer: c
Explanation: At high power densities all materials will evaporate if the energy can be absorbed. Thus, when welding in this way a hole is usually formed by evaporation. This “hole” is then traversed through the material with the molten walls sealing up behind it. The result is what is known as a “keyhole weld. This is characterized by its parallel sided fusion zone and narrow width.
7. Laser welding efficiency can be calculated by formula _____
a) Velocity*thickness/power
b) Velocity*power/thickness
c) Power*thickness/velocity
d) Velocity*thickness*power
Answer: a
Explanation: Efficiency = V.t/P, where
V = traverse speed, mm/s;
t = thickness welded, mm;
P = incident power, kW.
8. The heat source intensity for laser beam welding lies in the range _____
a) 10 5 -10 7
b) 10 5 -10 8
c) 10 10 -10 12
d) 10 12 -10 14
Answer: c
Explanation: The heat source intensities for various welding processes is as follows;
• Flux shield arc welding – 5*10 6 -10 8
• Gas shielded arc welding – 5*10 6 -10 8
• Plasma welding – 5*10 6 -10 10
• Laser beam or electron beam welding – 10 10 -10 12 .
9. The joining efficiency and the energy spent during the welding process are directly proportional.
a) True
b) False
Answer: a
Explanation: The higher the value of the joining efficiency the less energy is spent on unnecessary heating. Therefore-
• Lower heat affected zone
• Lower distortion in the workpieces.
10. Resistance welding has the smallest heat affected zone as compared to all welding processes.
a) True
b) False
Answer: b
Explanation: Resistance welding is most efficient in this respect because the fusion and heat affected zone energy is only generated at the high resistance interface to be welded. Laser and electron beam welding also have good efficiencies and high power densities.
This set of Advanced Manufacturing Processes Questions and Answers focuses on “Laser Welding – 5”.
1. In keyhole mode of laser welding, hole is stabilized by the _____
a) weld puddle
b) shielding gases
c) pressure of the vapour
d) laser beam
Answer: c
Explanation: In “keyhole” welding in which there is sufficient energy/unit length to cause evaporation and hence a hole in the melt pool. This hole is stabilized by the pressure from the vapour being generated.
2. In keyhole mode of laser welding, the keyhole behaves like _____
a) optical black body
b) an energy reflector
c) an energy amplifier
d) a shielding
Answer: a
Explanation: The “keyhole” behaves like an optical black body in that the radiation enters the hole and is subject to multiple reflections before being able to escape. Nearly all the beam energy is absorbed once the keyhole is formed.
3. Which of the following has the highest joining efficiency?
a) Acetylene flame welding
b) TIG welding
c) Electron beam welding
d) Laser welding
Answer: c
Explanation: The joining efficiencies for different welding processes is listed below;
Oxy-acetylene flame welding — 0.2-0.5
Manual arc welding – 2-3
TIG welding – 0.8-2
Electron beam welding – 20-30
Laser beam welding – 15-25.
4. Flow structures can directly affect the ____
a) laser wave formation
b) frozen bead
c) weld puddle
d) porosity
Answer: b
Explanation: The two principle areas of interest in laser beam welding are;
– Flow structures which directly affects the wave formation in the weld pool and frozen bead geometry
– Absorption mechanism
• Fresnel absorption
• Inverse Bremmstrahlung, leading to plasma re-radiation.
5. During laser welding, any hump on the surface can cause _____
a) increase in weld porosity
b) flow instability
c) higher energy absorption
d) decrease in the weld thickness
Answer: c
Explanation: Any hump on the surface will cause localized higher absorption and an explosion due to instantaneous evaporation. The keyhole walls are fluctuating with flow velocities up to 0.4 m/s.
6. The hot plasma vapour emerging from the keyhole may ionize _____
a) shielding gas
b) shroud gas
c) lasing material
d) workpiece material
Answer: b
Explanation: The keyhole contains considerable metal vapour, which is partially absorbing and hence capable of forming a plasma on further heating. This hot plasma vapour emerging from the keyhole may ionize the shroud gas. Ionized gas has free electrons and is thus capable of absorbing or even blocking the beam.
7. How many of the following process parameters can affect the welding process?
• Power pulses
• Wavelength
• Gap
• Joint geometries
a) 1
b) 2
c) 3
d) 4
Answer: d
Explanation: Following are the parameters that can affect the welding process:
• Beam Properties:
– Power, pulsed or continuous
– Spot size and mode
– Polarisation – Wavelength
• Transport Properties:
– Speed
– Focal position
– Joint geometries
– Gap tolerance.
8. Which of the following does not affect the operating characteristics in laser welding?
a) shroud gas composition
b) material surface conditions
c) component orientation
d) shroud design
Answer: c
Explanation: Following are the parameters that can affect the welding process:
• Shroud/shielding Gas Properties:
– Composition
– Shroud design
– Pressure/velocity
• Material Properties:
– Composition
– Surface condition.
9. The maximum welding speed varies directly with the power
a) True
b) False
Answer: a
Explanation: The maximum welding speed for a given thickness rises with an increase in power. The fall off shown at the higher power levels of 2kW could be attributed to the poorer mode structure given by most lasers when working at their peak power.
10. Pulse repletion factor is considered while determining the welding speed.
a) True
b) False
Answer: a
Explanation: The use of pulsed power allows two more variables:
– pulse repetition frequency ,
– % overlap to be considered.
The welding speed is decided by the following relation:
– spot size x PRF x .
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Welding – 6”.
1. Weld bead quality and the penetration are functions of _____
a) shroud gas velocity
b) material of the component
c) wavelength of the laser beam
d) power
Answer: d
Explanation: Penetration is a function of power and likewise the weld bead quality.
– Too much power causes vaporization and material ejection as in drilling
– Thus for welding the pulse is usually longer than for drilling and shaped to have a smaller initial peak.
2. Joining efficiency is dependent on _____
a) spot size
b) mode
c) polarisation
d) surface conditions
Answer: b
Explanation: In the laser welding process:
• The joining efficiency is greatly affected by the mode of the laser beam
• True TEM00 modes provide highest joining efficiencies.
3. Which of the following has no effect on laser welding?
a) Plane of polarisation
b) Joint geometries
c) Shroud gas composition
d) Wavelength
Answer: a
Explanation: Polarization should have no effect on laser welding since the beam is absorbed inside a keyhole and hence it should be absorbed regardless of the plane of polarization unlike cutting.
4. In some cases, polarisation can affect _____
a) weld fusion zones
b) power
c) focal position
d) spot size
Answer: a
Explanation: Some second order events have been noted by Beyer et al. which show the effect of polarization;
– variation in penetration
– the weld fusion zones are also wider for the case of s-polarisation .
5. At slow speeds, the beam is absorbed by _____ effects.
a) the george clooney
b) inverse Bremsstrahlung
c) acousto-optic
d) bridgman
Answer: b
Explanation: At slow speeds the plasma absorption dominates and the beam is absorbed by inverse Bremsstrahlung effects in the keyhole generating a plasma. Acousto-optic effects can be seen in the nonlinear optics field. Bridgman effect is used in electricity.
6. _____ is advantageous for CO 2 lasers.
a) High reflectivity
b) High absorptivity
c) Low reflectivity with short wave length
d) Low absorptivity with high wave length
Answer: c
Explanation: In welding with a conduction limited weld then the surface reflectivity becomes extremely important. The lower reflectivity with the shorter wavelengths gives a distinct advantage to Excimer, YAG or CO lasers over the CO 2 laser.
7. The effect of welding speed can be seen on ____
a) weld bead
b) penetration
c) power consumption
d) polarisation
Answer: a
Explanation: The effect of speed on the welding process is principally described by the
• Overall heat balance equation due to time for conduction
• Weld bead
• Shrouding high speed welds.
8. Which of the following is not affected by the speed of welding?
a) Pool size
b) Pool flow pattern
c) Weld bead
d) Focal position
Answer: d
Explanation: As the speed increases the pool flow pattern and size changes. At higher speeds, if the power is high enough and the pool large enough then undercut is produced which proceeds and edge freezing occurs leaving a slight undercut but the thread of the pool in the centre.
9. At slow speeds, smaller pool is formed.
a) True
b) False
Answer: b
Explanation: At slow speeds:
– the pool is large and wide and may result in drop out
– the ferrostatic head is too large for the surface tension to keep the pool in place and so it drops out of the weld leaving a hole or depression.
10. At high speeds, undercut occurs.
a) True
b) False
Answer: a
Explanation: At higher speeds:
– the strong flow towards the centre of the weld in the wake of the keyhole has no time to redistribute and is hence frozen as an undercut at the sides of the weld.
11. Which of the following lasers is suitable for welding of components made of aluminium?
a) Nd-YAG laser
b) Dye laser
c) Combination of CO and Excimer lasers
d) Combination of ruby and CO 2 lasers
Answer: c
Explanation: An Excimer and CO 2 laser beam combination showed improved coupling for the welding of high reflectivity materials, such as aluminium or copper could be obtained. Using two electron beams, the keyhole could be stabilized causing fewer waves on the weld pool and giving a better penetration and bead shape.
12. The improved coupling in case of welding of high reflectivity materials using twin beam lasers is due to _____
a) surface rippling
b) surface tension
c) surface smoothness
d) surface area
Answer: a
Explanation: The enhanced coupling was considered principally due to,
• altering the reflectivity by surface rippling caused by the Excimer
• a secondary effect coining from coupling through the Excimer generated plasma.
13. Which of the following is the problem on welding aluminium by laser welding?
a) Porosity
b) Cracking
c) Less grain growth
d) Brittle weld
Answer: a
Explanation: Following problems are faced while laser welding aluminium:
– High reflectivity
– Porosity
– Excessive fluidity.
14. Which of the following is the problem on welding heat resistant alloys by laser welding?
a) Brittle welds
b) Hot Cracking
c) Fluidity
d) High power consumption
Answer: a
Explanation: Following problems are faced while laser welding heat resistant alloys:
– Brittle welds
– Segregation problems
– Cracking.
15. Which of the following materials faces the problem of hot cracking while laser welding?
a) Inco 718
b) Steels
c) Hastelloy
d) Iridium alloys
Answer: d
Explanation: Problems faced during laser welding of materials like Inco718, Jetehet, M152, Hastelloy are-
– Weld is more brittle
– Segregation problems
– Cracking.
While laser welding Iridium alloys, there are chances of hot cracking. Steels can be laser welded very easily without any problems.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Laser Welding – 7”.
1. The difference between welding at long and short wavelengths is due to _____
a) high absorptivity
b) high reflectivity
c) polarisation
d) shroud design
Answer: a
Explanation: Due to the high absorptivity within the “keyhole” there is little operational difference when welding with long or short wavelengths. Shorter wavelengths do not get absorbed quickly by plasma therefore they are more useful in welding.
2. The pressure at the centre is a function of the _____
a) surface tension
b) joint geometries
c) material composition
d) gap tolerance
Answer: a
Explanation: The centre has a pressure which is a function of the surface tension and the curvature. This leads to pressure instability causing the “pinch” effect. The regions of high curvature flow to regions of lower curvature resulting in large humps.
3. The gap between the components should be smaller than _____
a) half of the beam diameter
b) beam diameter
c) square of the beam diameter
d) one quarter of the beam diameter
Answer: a
Explanation: In butt joints, the gap must be small enough that the beam cannot pass straight through the joint. The gap should be smaller than half the beam diameter .
4. For welds having larger gaps,_____
a) the beam is rotated
b) an extra lens is added
c) high energy density beam is used
d) zif-zag welds are made
Answer: a
Explanation: For welds where there is a large gap the beam is sometimes rotated by rotating the lens off axis from the beam. Also, there is a chance of some drop out or an underfill in the weld.
5. The welds which do not require filler material are called _____ materials.
a) autogenous
b) autofiller
c) non-filler
d) isotropic
Answer: a
Explanation: The welds which do not require filler material are called “autogenous” materials. If there are larger gaps, they can be corrected by adding filler material as a wire or powder.
6. Which of the following is not affected by the gas shroud?
a) Formation of plasma
b) Hindrance to the beam
c) Absorption of the beam
d) Pool width
Answer: d
Explanation: The gas shroud can affect the formation of plasma which may block the beam and thus the absorption of the beam into the workpiece. The formation of plasma is thought to occur through the reaction of the hot metal vapours from the keyhole with the shroud gas.
7. The shroud gas enters the keyhole because of _____
a) the fast emission of vapour from the keyhole
b) the narrower shape of the keyhole
c) higher wavelength of the beam
d) molten material
Answer: a
Explanation: The shroud gas enters the keyhole because of the fast emission of vapour from the keyhole. The plasma blocking effect will be less for those gases having a high ionization potential.
8. Which of the following gases is most favourable as shrouding gases in laser welding?
a) Oxygen
b) Helium
c) Argon
d) Chlorine
Answer: b
Explanation: Helium is favoured, in spite of its price, as the top shroud gas in laser welding. The shroud underneath the weld would be of a cheaper gas e.g. argon, N 2 or CO 2 .
9. How many issues are there concerning laser welding?
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: The main issues laser welding are:
– crack sensitivity,
– porosity,
– HAZ embrittlement
– poor absorption of the radiation.
10. In case of laser welding of dissimilar metals, there are chances of formation of _____
a) porous welds
b) brittle welds
c) thin welds
d) cracks
Answer: b
Explanation: For welds of dissimilar metals there is the additional problem of the possible formation of brittle intermetallics. Crack sensitivity of the material refers to centreline cracking, hot cracking or liquation.
11. Cracking happens due to _____
a) shrinkage stress
b) improper gas shielding
c) high weld speeds
d) high wavelength
Answer: a
Explanation: It is due to the shrinkage stress building up before the weld is fully solidified and strong enough to take the stress. It usually happens in metal alloys having a wide temperature range over which solidification occurs, e.g. those with high C, S, and P contents.
12. The temperature required for using arc augmented welding phenomenon is around _____
a) 100 °C
b) 200 °C
c) 300 °C
d) 400 °C
Answer: c
Explanation: In arc augmented laser welding the arc from a TIG torch mounted close to the laser beam interaction point will automatically lock onto the laser generated hot spot. The temperature required for this phenomenon is around 300 °C above the surrounding temperature.
13. Arc Augmented Laser Welding is used for _____
a) higher penetration
b) reducing power loss
c) stabilizing the arc
d) improve wed quality
Answer: c
Explanation: Arc Augmented Laser Welding is used for either to stabilize an arc which is unstable due to its traverse speed or to reduce the resistance of an arc which is stable.
14. The arc is on the same side of the workpiece as the laser.
a) True
b) False
Answer: a
Explanation: The arc is on the same side of the workpiece as the laser which allows doubling of the welding speed for a modest increase in the capital cost. The locking only happens for arcs with a low current and therefore slow cathode jet.
15. Weld pool geometry can be controlled by using multiple laser beams.
a) True
b) False
Answer: a
Explanation: If two laser beams are used simultaneously then there is the possibility of controlling the weld pool geometry and the weld bead shape. It is known as twin beam laser welding.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 1”.
1. The metal is said to be cold worked if it is plastically deformed at temperatures lower than _____
a) sublimation point
b) critical point
c) melting point
d) saturation point
Answer: c
Explanation: When a metal is plastically deformed at temperatures that are low relative to its melting point, it is said to be cold worked. A rough rule-of-thumb is to assume that plastic deformation corresponds to cold working if it is carried out at temperatures lower than one-half of the melting point measured on an absolute scale.
2. The fraction of total energy stored in the material _____ with increasing deformation.
a) increases
b) decreases
c) first increases and then decreases
d) remains constant
Answer: b
Explanation: Most of the energy expended in cold work appears in the form of heat, but a finite fraction is stored in the metal as strain energy associated with various lattice defects created by the deformation. The stored energy increases with increasing deformation, but at a decreasing rate, so that the fraction of the total energy stored decreases with increasing deformation.
3. The amount of stored energy can be greatly increased by _____
a) lowering the deformation temperature
b) increasing the deformation temperature
c) increasing the purity of the metal
d) reducing the net volume
Answer: a
Explanation: The amount of stored energy can be greatly increased by,
• increasing the severity of the deformation
• lowering the deformation temperature
• changing the pure metal to an alloy.
4. A soft annealed metal can have dislocation densities of the order of _____
a) 10 5 to 10 6 m -2
b) 10 8 to 10 10 m -2
c) 10 10 to 10 12 m -2
d) 10 10 to 10 15 m -2
Answer: c
Explanation: Cold working is known to increase greatly the number of dislocations in a metal. A soft annealed metal can have dislocation densities of the order of 10 10 to 10 12 m -2 , and heavily cold-worked metals can have approximately 10 16 .
5. Strain energy of the metal _____ with increasing the dislocation densities.
a) increases
b) decreases
c) does not change
d) first decreases and then remains constant
Answer: a
Explanation: Since each dislocation represents a crystal defect with an associated lattice strain, increasing the dislocation density increases the strain energy of the metal. Cold working is able to increase the number of dislocations in metal by a factor as large as 10 4 to 10 6 .
6. Vacancies in the metal lattice will be formed in greater numbers than interstitial atoms during _____
a) plastic deformation
b) brittle deformation
c) heating over melting temperature
d) non-linear deformation
Answer: a
Explanation: Since the strain energy associated with a vacancy is much smaller than that associated with an interstitial atom, it can be assumed that vacancies will be formed in greater numbers than interstitial atoms during plastic deformation.
7. Which of the following relations is true?
a) ΔG = ΔH – TΔS
b) ΔH = ΔG – TΔS
c) ΔT = ΔH – GΔS
d) ΔG = TΔH – ΔS
Answer: a
Explanation: ΔG = ΔH – T ΔS, this equation is known as Gibb’s free energy equation. While plastic deformation certainly increases the entropy of a metal, the effect is small compared to the increase in internal energy . The term T∆S in the free energy equation may be neglected and the free-energy increase equated directly to the stored energy. Where ∆G is the free energy associated with the cold work, ∆H is the enthalpy or stored strain energy, ∆S is the entropy increase due to the cold work, and T is the absolute temperature.
8. Free energy of cold-worked metals is _____ than/as that of annealed metals.
a) greater
b) lower
c) same
d) greater of few metals
Answer: a
Explanation: Since the free energy of cold-worked metals is greater than that of annealed metals, they may soften spontaneously. Heating a deformed metal greatly speeds up its return to the softened state.
9. The anisothermal anneal method, the energy release is determined as a function of temperature.
a) True
b) False
Answer: a
Explanation: The anisothermal anneal method, the cold worked metal is heated continuously from a lower to a higher temperature and the energy release is determined as a function of temperature. One form of the anisothermal anneal measures the difference in the power required to heat two similar specimens at the same rate.
10. The one specimen form above mentioned specimen is cold worked.
a) True
b) False
Answer: a
Explanation: One specimen of the two is cold worked before the heating cycle, while the other serves as a standard and is not deformed. During the heating cycle, the cold-worked specimen undergoes reactions that release heat and lower the power required to heat it in comparison with that required to heat the standard specimen. Measurements of the difference in power give direct evidence of the rate at which heat is released in the cold-worked specimen.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 2”.
1. In _____ annealing, the energy is measured while the specimen is maintained at a constant temperature.
a) isothermal
b) adiabatic
c) anisothermal
d) isentropic
Answer: a
Explanation: The other method of studying energy release involves isothermal annealing. Here the energy is measured while the specimen is maintained at a constant temperature. The large energy releases appear simultaneously with the growth of an entirely new set of essentially strain-free grains, which grow at the expense of the original badly deformed grains.
2. Which of the following is not a microstructural change occurring in the metal while is plastic deformation?
a) change in grain size
b) strain hardening
c) formation of metallic bonds
d) change in dislocation density
Answer: c
Explanation: Plastic deforming a polycrystalline metal specimen at temperatures that are low relative to its absolute melting temperature produces microstructural and property changes that include a change in grain size, strain hardening, and an increase in dislocation density.
3. Properties such as _____ may be modified as a consequence of plastic deformation.
a) electrical conductivity
b) tensile strength
c) malleability
d) weldability
Answer: a
Explanation: Properties such as electrical conductivity and corrosion resistance may be modified as a consequence of plastic deformation. These properties and structures may revert back to the precold-worked states by an annealing treatment. Such restoration results from two different processes that occur at elevated temperatures: recovery and recrystallization, which may be followed by grain growth.
4. During recovery, some of the stored internal strain energy is relieved by virtue of _____
a) increased grain size
b) molten metal
c) dislocation movements
d) high temperature
Answer: c
Explanation: During recovery, some of the stored internal strain energy is relieved by virtue of dislocation motion, as a result of enhanced atomic diffusion at the elevated temperature.
5. During recovery, there is some reduction in the ______
a) number of grains
b) number of dislocations
c) tensile strength of the metal
d) strain energy
Answer: b
Explanation: There is some reduction in the number of dislocations, and dislocation configuration are produced having low strain energies. Physical properties such as electrical and thermal conductivities and the like are recovered to their precold worked states. However, even after recovery is complete, the grains are still in a relatively high strain energy state.
6. The driving force to produce new grain structure is the difference ______ between the strained and unstrained material.
a) entropy
b) temperature
c) internal energy
d) conductivity
Answer: c
Explanation: The driving force to produce new grain structure is the difference in internal energy between the strained and unstrained material. The new grains form as very small nuclei and grow until they completely consume the parent material, processes that involve short-range diffusion.
7. During recrystallization, the metal becomes _____
a) harder
b) soft
c) brittle
d) malleable
Answer: b
Explanation: During recrystallization, the metal becomes softer, weaker, yet more ductile. Recrystallization of cold-worked metals may be used to refine the grain structure.
8. The degree of recrystallization increases with _____
a) temperature
b) softness
c) time
d) strain energy
Answer: c
Explanation: Recrystallization is a process the extent of which depends on both time and temperature. The degree of recrystallization increases with time. Metal becomes soft due to recrystallization but they are not dependent on each other.
9. Recrystallization is the formation of a new strain-free grain.
a) True
b) False
Answer: a
Explanation: Recrystallization is the formation of a new set of strain-free and equiaxed grains that have low dislocation densities and are characteristic of the precold-worked condition.
10. Recrystallization temperature is the temperature at which molten metal starts solidifying.
a) True
b) False
Answer: b
Explanation: Recrystallization temperature is the temperature at which recrystallization just reaches completion in 1 hr. Typically it is between one-third and one-half of the absolute melting temperature of a metal or alloy and depends on several factors, including the amount of prior cold work and the purity of the alloy.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 3”.
1. The rate of recrystallization can be enhanced by ______
a) increasing the temperature
b) increasing the percentage of cold work
c) increasing the rate of cooling
d) applying pressure
Answer: b
Explanation: Increasing the percentage of cold work enhances the rate of recrystallization, with the result that the recrystallization temperature is lowered, and approaches a constant or limiting value at high deformations.
2. The critical degree of cold work lies between _____ of cold work.
a) 2% and 20%
b) 5% and 10%
c) 7% and 15%
d) 20% and 30%
Answer: a
Explanation: There exists some critical degree of cold work below which recrystallization cannot be made to occur; normally, this is between 2% and 20% cold work.
3. The recrystallization in pure metal is faster than in _____
a) non-metals
b) alloys
c) polymers
d) d-block metals
Answer: b
Explanation: Recrystallization proceeds more rapidly in pure metals than in alloys. It is believed that impurity atoms preferentially segregate at and interact with these recrystallized grain boundaries so as to diminish their mobilities; this results in a decrease of the recrystallization rate and raises the recrystallization temperatures.
4. For pure metals, the recrystallization temperature is normally _____
a) equal to T m
b) 0.5 T m
c) 0.8 T m
d) 0.3 T m
Answer: d
Explanation: For pure metals, the recrystallization temperature is normally 0.3 T m , where T m is the absolute temperature; for some commercial alloys it may run as high as 0.7 T m .
5. In hot working, plastic deformation operations are often carried out at temperatures above the ______ temperature.
a) melting
b) recrystallization
c) room
d) cold working
Answer: b
Explanation: Plastic deformation operations are often carried out at temperatures above the recrystallization temperature in a process termed hot working. The material remains relatively soft and ductile during deformation because it does not strain harden, and thus large deformations are possible.
6. Which of the following metals has recrystallization temperature below 0⁰C?
a) Pb
b) Zn
c) Al
d) Cu
Answer: a
Explanation: Recrystallization temperatures of these metals are as follows,
• Pb: -4⁰C
• Zn: 10⁰C
• Al: 80⁰C
• Cu: 120⁰C.
7. Which of the following metals has recrystallization temperature above 1000⁰C?
a) Cu- Zn alloy
b) Ni
c) Fe
d) W
Answer: d
Explanation: Recrystallization temperatures of these metals are as follows,
• Cu- Zn alloy: 475⁰C
• Ni: 370⁰C
• Fe: 450⁰C
• W: 1200⁰C.
8. Cold working increases ______ of the metal.
a) hardness
b) ductility
c) melting point
d) conductivity
Answer: a
Explanation: Cold working increases strength, hardness, and electrical resistance, and it decreases ductility. In the recovery stage of annealing, the physical and mechanical properties that suffered changes as a result of cold working tend to recover their original values.
9. Yield strength is the stress corresponding to point of intersection of stress-strain curve and strain offset line.
a) True
b) False
Answer: a
Explanation: A convention has been established wherein a straight line is constructed parallel to the elastic portion of the stress-strain curve at some specified strain offset, usually 0.002. The stress corresponding to the intersection of this line and the stress-strain curve as it bends over in the plastic region is defined as the yield strength.
10. The stress level at which plastic deformation begins is known as the proportional limit point.
a) True
b) False
Answer: b
Explanation: The stress level at which plastic deformation begins is known as yield point. For metals that experience this gradual elastic-plastic transition, the point of yielding may be determined as the initial departure from linearity of the stress-strain curve, as indicated by point P on the stress-strain curve and it is known as proportional limit.
This set of Tricky Manufacturing Processes Questions and Answers focuses on “Annealing – 4”.
1. The yield point can be completely recovered in a zinc crystal at _____
a) room temperature
b) 32⁰C
c) 50⁰C
d) 88⁰C
Answer: a
Explanation: Recovery of the yield point thus begins very rapidly. The yield point can be completely recovered in a zinc crystal at room temperature in a period of a day. The stress-strain diagrams indicate a well-known fact: the rate at which a property recovers isothermally is a decreasing function of the time.
2. Polygonization is associated with_____
a) grain size
b) plastically bent crystals
c) conductivity
d) strength of the material
Answer: b
Explanation: Another recovery process is called polygonization. In its simplest form it is associated with crystals that have been plastically bent. Many workers have shown that the Laue spots of bent crystals assume a fine structure after a recovery anneal .
3. Polygonization is a process of _____
a) annealing a bent crystal
b) annealing a pure metal
c) heating the metal above recrystallization temperature
d) quenching
Answer: a
Explanation: When a bent crystal is annealed, the curved crystal breaks up into a number of closely related small perfect crystal segments. This process has been given the name polygonization.
4. The regrouping of edge dislocations into low-angle boundaries helps in _____
a) lowering the strain energy
b) increasing the stored energy
c) lowering the recrystallization temperature
d) increasing the strength of the metal
Answer: a
Explanation: In addition to lowering the strain energy, the regrouping of edge dislocations into low-angle boundaries has a second important effect. This is the removal of general lattice curvature. As a result of polygonization, crystal segments lying between a pair of low-angle boundaries approach the state of strain-free crystals with flat uncurved planes.
5. An edge dislocation is capable of moving by a climb in a direction _____ to the slip plane.
a) 30⁰
b) 45⁰
c) 90⁰
d) 180⁰
Answer: c
Explanation: An edge dislocation is capable of moving either by slip on its slip plane or by a climb in a direction perpendicular to its slip plane. The driving force for these movements comes from the strain energy of the dislocations, which decreases as a result of polygonization.
6. The rate of polygonization increases rapidly with _____
a) density
b) temperature
c) humidity
d) grain size
Answer: b
Explanation: The strain field of dislocations grouped on slip planes produces an effect force that makes them move into sub-boundaries. This force exists at all temperatures, but at low temperatures edge dislocations cannot climb. Since dislocation climb depends on the movement of vacancies , the rate of polygonization increases rapidly with temperature.
7. As the polygon walls become more widely separated, the rate of ______becomes a decreasing function of time and temperature.
a) polygonization
b) decay
c) coalescence
d) grain growth
Answer: c
Explanation: As the polygon walls become more widely separated, the rate of coalescence becomes a decreasing function of time and temperature so that the polygonization process approaches a more or less stable state with widely spaced, approximately parallel sub-boundaries.
8. The rate at which a recovery process occurs always decreases with _____
a) temperature
b) time
c) yield strength
d) ductility
Answer: b
Explanation: In an isothermal anneal, the rate at which a recovery process occurs always decreases with time; that is, it starts rapidly and proceeds at a slower and slower rate as the driving force for the reaction is expended.
9. In deformed polycrystalline metals, high-temperature recovery is considered to be essentially a matter of polygonization.
a) True
b) False
Answer: a
Explanation: In deformed polycrystalline metals, high-temperature recovery is considered to be essentially a matter of polygonization and annihilation of dislocations. At lower temperatures other processes such as occur in dynamic recovery are of greater importance, current theories picture the recovery process as primarily a matter of reducing the number of point defects to their equilibrium value.
10. Recrystallization during an isothermal anneal begins very slowly.
a) True
b) False
Answer: a
Explanation: Recrystallization during an isothermal anneal begins very slowly, and builds up to a maximum reaction rate, after which it finishes slowly. Recovery processes start at the beginning of the annealing cycle and account for the initial energy release, while recrystallization starts later and accounts for the second energy release.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 5”.
1. How many factors are there to determine isothermal phase transformation in terms of time and temperature?
a) 1
b) 3
c) 7
d) 5
Answer: d
Explanation: The factors that determine isothermal phase transformation in terms of time and temperature are,
• The nucleation rate
• The growth rate
• The density and distribution of nucleation sites
• The overlap of diffusion fields from adjacent transformation volume
• The impingement of adjacent transformed volumes.
2. The time needed to finish the recrystallization is inversely proportional to _____
a) surface area
b) volume
c) temperature
d) distribution of grains
Answer: c
Explanation: The higher the temperature, the shorter the time needed to finish the recrystallization. Recrystallization starts after the recover and accounts for the second energy release.
3. The ______ generally does not remain a constant throughout the recrystallization process.
a) strain energy
b) activation energy
c) threshold energy
d) recrystallization energy
Answer: b
Explanation: Modern recrystallization theory indicates that the activation energy generally does not remain a constant throughout the recrystallization process. In most cases, the activation energy changes continuously during recrystallization as the driving force for recrystallization, the stored energy of cold work, is depleted.
4. Recrystallization temperature is the temperature at which a particular metal _______
a) starts melting
b) starts solidifying
c) starts recrystallizing
d) completely recrystallizes
Answer: d
Explanation: Recrystallization temperature is the temperature at which a particular metal with a particular amount of cold deformation will completely recrystallized in a finite period of time, usually 1 hr.
5. ______ is a means of mechanical deformation used on cylindrical rods.
a) Swaging
b) Swishing
c) Hammering
d) Bending
Answer: a
Explanation: Swaging is a means of mechanical deformation used on cylindrical rods in which the diameter of the rod is reduced uniformly by a mechanical hammer equipped with rotating dies.
6. Recrystallization is promoted by ______
a) increasing temperature
b) increasing cold work
c) decreasing grain size
d) decreasing temperature
Answer: b
Explanation: Recrystallization is promoted by increasing amounts of cold work. When annealed at the same temperature, the metal with the larger amount of cold work recrystallizes much faster than that with the lesser reduction.
7. The recrystallization temperature is lowered by _____
a) increasing the surface area of the component
b) increasing the amount of cold work
c) keeping the metal in cold environment
d) decreasing the amount of cold work
Answer: b
Explanation: The temperature at which the metal recrystallizes completely within an hour is lower for a greater amount of cold work. The amount of cold work is measured in terms of the percentage reduction in the area of the cylindrical cross-section.
8. The recrystallization temperature is ______
a) a time dependent function
b) a material property
c) an independent function
d) dependent on polygonization rate
Answer: b
Explanation: To the practical engineer, the sensitivity of the recrystallization process to small changes in temperature makes it appear as though the metal has a fixed temperature, below which it will not recrystallize, and for this reason, there is a tendency to regard the recrystallization temperature as a property of the metal and to neglect the time factor in recrystallization.
9. The origin of a recrystallized grain is always a pre-existing misoriented region.
a) True
b) False
Answer: a
Explanation: The origin of a recrystallized grain is always a pre-existing region that is highly misoriented in relation to the material surrounding it. This high degree of misorientation gives the region from which the new grain originates the needed growth mobility.
10. Activation energy for recrystallization is dependent on the amount of deformation.
a) True
b) False
Answer: a
Explanation: The temperature dependence of recrystallization varies with the amount of cold work, or that the activation energy for recrystallization is a function of the amount of deformation.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 6”.
1. The rate at which a metal recrystallizes depends on the rate of ______
a) cooling
b) polygonization
c) nuclei formation
d) grain growth
Answer: c
Explanation: The rate at which a metal recrystallizes depends on the rate at which nuclei form, and also on the rate at which they grow. These two rates also determine the final grain size of a recrystallized metal.
2. The grain size will be smaller when ______
a) nuclei form rapidly and grow slowly
b) nuclei form slowly and grow rapidly
c) recrystallization temperature is high
d) activation energy is low
Answer: a
Explanation: If nuclei form rapidly and grow slowly, many crystals will form before their mutual impingement completes the recrystallization process. In this case, the final grain size is small. On the other hand, it will be larger if the rate of nucleation is small compared to the rate of growth.
3. The number of nuclei that form per second is called as _____
a) recrystallization frequency
b) nucleation frequency
c) nuclei growth frequency
d) grain growth frequency
Answer: b
Explanation: It is customary to define the nucleation frequency, N, as the number of nuclei that form per second in a cubic centimetre of unrecrystallized matrix. The grain size is dependent on the rate of formation and growth of nuclei.
4. The time rate of change of the diameter of a recrystallized grain is known as_____
a) diameter rate
b) linear growth rate
c) growth rate
d) nucleation rate
Answer: b
Explanation: The linear rate of growth, G, is defined as the time rate of change of the diameter of a recrystallized grain. In practice, G is measured by annealing for different lengths of time a number of identical specimens at a chosen isothermal temperature.
5. The variation of this diameter with isothermal annealing time gives the _____
a) nucleation rate
b) linear rate of growth
c) grain size change rate
d) diametrical growth rate
Answer: b
Explanation: The variation of this diameter with isothermal annealing time gives the rate of growth, G. The diameter of the largest grain in each specimen is measured after the specimens are cooled to room temperature and prepared metallographically.
6. The rate of nucleation can be defined as______
a) number of grains per unit area
b) number of grains per unit volume
c) number of nuclei formed per unit area per unit time
d) number of grains formed per nuclei
Answer: a
Explanation: The rate of nucleation can be determined from the same metallographic specimens by counting the number of grains per unit area on the surface of each.
7. For ______ nucleation will take place preferentially at highly energetic sites.
a) pure metals
b) alloys
c) polycrystalline
d) brittle
Answer: c
Explanation: For polycrystalline materials, nucleation will take place preferentially at highly energetic sites, such as grain-boundary triple points, original grain boundaries, and boundaries between deformation bands.
8. The nuclei may form by ______
a) grain growth
b) sub-grain growth
c) nuclei boundary growth
d) combining multiple grains
Answer: b
Explanation: The nuclei may form by subgrain growth and/or grain boundary migration. As a result of polygonization, it might be possible to produce a subgrain capable of growing out into the surrounding polygonized matrix.
9. In recrystallization, an entirely new set of grains is formed.
a) True
b) False
Answer: a
Explanation: In recrystallization, an entirely new set of grains is formed. New crystals appear at points of high-lattice-strain energy, such as slip-line intersections, deformation twin intersections, and in areas close to grain boundaries. In each case, it appears at points of strong lattice curvature.
10. A region of a crystal can become a nucleus and grow only if its size exceeds some minimum value.
a) True
b) False
Answer: a
Explanation: A number of models have been proposed, these models are in general agreement on 2 points. First, a region of a crystal can become a nucleus and grow only if its size exceeds some minimum value. The other condition for the formation of a nucleus is that it becomes surrounded by the equivalent of a high-angle grain boundary. This condition is required because the mobility of an arbitrary low-angle grain boundary is normally very low.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 7”.
1. Polygonization is essentially completed before the start of ______
a) solidification
b) recrystallization
c) cooling
d) grain growth
Answer: b
Explanation: Polygonization is essentially completed before the start of recrystallization, the stored energy can be assumed to be confined to the dislocations in polygon walls. The elimination of the sub-boundaries is a basic part of the recrystallization process.
2. The recrystallized grain size is the crystal size immediately at the end of ______
a) polygonization
b) deformation
c) recrystallization
d) 1 hr from the start of the recrystallization
Answer: c
Explanation: The recrystallized grain size is the crystal size immediately at the end of recrystallization, that is before grain growth proper has had a chance to occur. The recrystallized grain size depends upon the amount of deformation given to the specimens before annealing.
3. The grain size grows rapidly with decreasing ______
a) temperature
b) deformation
c) yield strength
d) hardness
Answer: b
Explanation: The grain size grows rapidly with decreasing deformation. Too little deformation, however, will make recrystallization impossible in any reasonable length of time.
4. The critical amount of cold work is the ______
a) minimum amount of cold work that allows recrystallization
b) maximum amount of cold work that allows recrystallization
c) amount of cold work need to recover the specimen
d) amount of cold work needed to increase the yield strength by 10 MPa
Answer: a
Explanation: For very small deformation there will be no recrystallization in the specimen. This leads to the concept of the critical amount of cold work, which may be defined as the minimum amount of cold deformation that allows the specimen to recrystallize .
5. The critical deformation is not dependent on ______
a) material properties
b) tension
c) torsion
d) compression
Answer: a
Explanation: The critical deformation is not a property of the metal since its value varies with the type of deformation; for example — tension, torsion, compression, rolling, bending, etc.
6. Plastic deformation occurs without roughing of the surface if the grain size of the metal is less than _____ in diameter.
a) 0.002 mm
b) 0.05 mm
c) 0.1 mm
d) 1 mm
Answer: b
Explanation: If the grain size of metal is very small , plastic deformation occurs without appreciable roughing of the surface ü.
7. If the diameter of the average grain is large, cold working produces _____
a) smooth surface
b) roughened surface
c) highly tensed surface
d) cracks
Answer: b
Explanation: If the diameter of the average grain is large, cold working produces a roughened, objectionable surface. Such a phenomenon is frequently identified by the term orange peel effect because of the similarity of the roughened surface to that of the peel of a common orange.
8. Which of the following is responsible for the orange-peel effect?
a) Large diameter
b) Isotropic nature of the material
c) Anisotropic nature of the material
d) Deformation
Answer: c
Explanation: The anisotropic nature of plastic strain inside crystals is directly responsible for the orange-peel effect, and the larger the crystals the more evident will be the nonhomogeneous nature of the deformation.
9. Critical deformation may exceed several hundred percent in case of deformation due to easy glide.
a) True
b) False
Answer: a
Explanation: In single crystals of hexagonal metals, when deformation occurs by an easy glide, the critical deformation may exceed several hundred percent. Twisting the same crystal to a few percent strain, however, may make it possible to recrystallize the specimen.
10. In metal that is cold-rolled, it is relatively easy to avoid a critical amount of cold work.
a) True
b) False
Answer: a
Explanation: In metal that is cold-rolled or drawn cold through dies , it is relatively easy to avoid a critical amount of cold work because the metal is more or less uniformly deformed.
This set of Manufacturing Processes Objective Questions & Answers focuses on “Annealing – 8”.
1. The ratio of ______ is frequently used in the interpretation of recrystallization data.
a) yield strength of test specimen and standard specimen
b) temperature and time
c) rate of nucleation and rate of growth
d) rate of recrystallization and polygonization
Answer: c
Explanation: The ratio of the rate of nucleation to the rate of growth, N to G, is frequently used in the interpretation of recrystallization data. If it is assumed that both N and G are constant or are average values for an isothermal recrystallization process, then the recrystallized grain size can be deduced from this ratio.
2. Many nuclei will form before the recrystallization process is completed if the ratio of the rate of nucleation to the rate of growth is _____
a) high
b) low
c) equal to 1
d) higher than rate of grain growth
Answer: a
Explanation: If the ratio is high, many nuclei will form before the recrystallization process is completed, and a fine-grain size will result. On the other hand, a low ratio corresponds to a slow rate of nucleation relative to the rate of growth, and to a coarse crystal size in a recrystallized specimen.
3. The ratio N to G decreases in magnitude with decreasing _____
a) temperature
b) stress
c) strain
d) grain size
Answer: c
Explanation: As the deformation before annealing is reduced to smaller and smaller values, the rate of nucleation falls much faster than the rate of growth. As a consequence, the ratio N to G decreases in magnitude with decreasing strain and is effectively zero at several percent elongation.
4. The rate of recrystallization is dependent upon how many variables?
a) 2
b) 3
c) 4
d) It is an independent value
Answer: c
Explanation: The rate of recrystallization is dependent upon the following variables:
• temperature of annealing and
• amount of deformation
• purity of the metal
• initial grain size
The recrystallized grain size is independent of the annealing temperature but sensitive to the amount of strain.
5. Which of the following materials has rapid rates of recrystallization?
a) Pure metals
b) Alloys
c) Ductile metals
d) Coinage metal
Answer: a
Explanation: Extremely pure metals have very rapid rates of recrystallization. As little as 0.01% of a foreign atom in solid solution can raise the recrystallization temperature by several hundred degrees.
6. The increase in the recrystallization temperature caused due to foreign atoms depends on _____
a) nature of foreign atoms
b) temperature of foreign atoms
c) size of foreign atoms
d) electronegativity of foreign atoms
Answer: a
Explanation: The increase in the recrystallization temperature caused by the presence of foreign atoms depends markedly upon the nature of the solute atoms. The fact that very small numbers of solute atoms have such a pronounced effect on recrystallization rates is believed to indicate that the solute atoms interact with grain boundaries.
7. Decreasing the grain size increases the _____
a) recrystallization time
b) nucleation rate
c) grain boundary area
d) recrystallization temperature
Answer: c
Explanation: Decreasing the grain size increases the grain-boundary area and, as a consequence, the volume and uniformity of distorted metal . This effect increases the number of possible sites of nucleation and, therefore, the smaller the grains of the metal before cold work, the greater will be the rate of nucleation and the smaller the recrystallized grain size for a given degree of deformation.
8. _____ is the driving force for grain growth.
a) Strain
b) Surface energy
c) Recrystallization
d) Surface hardness
Answer: b
Explanation: The driving force for grain growth lies in the surface energy of the grain boundaries. As the grain grow in size and their numbers decrease, the grain boundary area diminishes and the total surface energy is lowered accordingly.
9. Annealing of a slightly deformed metal specimen can lead to a localized, very coarse-grain growth.
a) True
b) False
Answer: a
Explanation: If only a portion of a metallic object is deformed cold, a region containing a critical amount of cold work must exist between the worked and unworked areas. Annealing in this case can easily lead to a localized, very coarse-grain growth.
10. Foreign atoms lowers the recrystallization rates.
a) True
b) False
Answer: a
Explanation: When a foreign atom migrates to a grain boundary, both its elastic field, as well as that of the boundary, are lowered. In recrystallization, grain-boundary motion occurs as the nuclei form and grow. The presence of foreign atoms in atmospheres associated with these boundaries strongly retards their motion and therefore lowers the recrystallization rates.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 9”.
1. Grain cells having a number of sides _____ have grain walls which are concave inwards.
a) >3
b) <6
c) <8
d) >5
Answer: b
Explanation: The cells with less than 6 sides have walls that are primarily concave toward their centres. Those cells with more than 6 sides have walls convex toward their centres, this effect is more pronounced the larger the number of sides above 6.
2. Grain cells with _____ sides are unstable.
a) <3
b) >8
c) <6
d) >10
Answer: c
Explanation: All grain cells with less than 6 sides are basically unstable and tend to shrink in size and these grains will therefore shrink and eventually disappear during annealing; while grain cells with more than 6 sides tend to grow in size.
3. If the grain has 6 boundaries, the structure will be _____
a) stable
b) metastable
c) quasi-stable
d) non-planner
Answer: b
Explanation: If the grain has 6 boundaries, they will be planar and the structure metastable. However, if the total number of boundaries around grain is less than 6, each boundary must be concave inwards.
4. Grain boundary migration occurs to _____
a) increase the strain energy
b) increase the surface hardness
c) reduce grain boundary energy
d) reduce recrystallization temperature
Answer: c
Explanation: Large grains will have more than 6 boundaries and will grow. The overall result of boundary migration is to reduce the number of grains, thereby increasing the mean grain size and reducing the total grain boundary energy. This phenomenon is known as grain growth or grain coarsening.
5. The phenomenon of formation of grain boundary of much lower surface energy than that of the average boundary is known as _____
a) grain boundary coalescence
b) atomic coalescence
c) geometrical coalescence
d) grain boundary migration
Answer: c
Explanation: Geometrical coalescence can be simply described as an encounter of 2 grains whose relative orientations are such that the boundary formed between the 2 grains is one of much lower surface energy than that of the average boundary. In a polycrystalline metal, such a boundary would be equivalent to a sub-grain boundary.
6. The boundary atoms in the crystal on the _____ of the boundary are more tightly bound than the boundary atoms in the crystal in the _____
a) concave side, convex side
b) convex side, concave side
c) surface, inner side
d) surface, concave side
Answer: a
Explanation: The boundary atoms in the crystal on the concave side of the boundary are more tightly bound than the boundary atoms in the crystal in the convex side because they are more nearly surrounded by neighbouring atoms of the same crystal.
7. The rate at which atoms jumps from ______ is greater than that in the opposite direction.
a) convex side to concave side of the grain
b) surface high strain energy to surface of low strain energy
c) grain at higher temperature to grain at lower temperature
d) concave side to convex side of the grain
Answer: a
Explanation: Tighter binding of the atoms on the concave side of the boundary should make the rate at which atoms jump across the boundary from the convex to the concave crystal greater than that in the opposite direction. The greater the curvature of the boundary, then the greater should be this effect, and faster the movement of the crystal boundary.
8. If _________ then there will be an elastic stress field introduced into the lattice.
a) number of foreign atoms is more than that of parent crystal atoms
b) number of foreign atoms is less than that of parent crystal atoms
c) size of foreign atoms is different than that of the parent crystal atoms
d) temperature of foreign atoms is different than that of parent crystal atoms
Answer: c
Explanation: If the size of a foreign atom and that of the parent crystal are different, then there will be an elastic stress field introduced into the lattice by each foreign atom.
9. The strain energy of the grain boundary can be reduced by migration of the foreign atoms into the pure crystal grain.
a) True
b) False
Answer: a
Explanation: Since grain boundaries are regions of lattice misfit, the strain energy of the boundary, as well as that of the lattice surrounding a foreign atom, can be reduced by the migration of the foreign atom to the neighbourhood of the grain boundary.
10. Higher the temperature faster will be the grain growth.
a) True
b) False
Answer: a
Explanation: As the metal approaches 100% purity, the grain-growth exponent increases toward the theoretical value ½. Also, note that at the higher temperature the rate of approach is faster.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 10”.
1. Temperature dependence of the grain-growth can be explained by ______
a) recrystallization theory
b) planks theory
c) assuming that grain boundaries brake due to thermal vibrations
d) strain energy theory
Answer: c
Explanation: The temperature dependence of the grain-growth exponent can be explained by assuming that the grain-boundary solute atmospheres are broken up by thermal vibrations at high temperatures. Those elements that distort the lattice structure the most have the largest effect on the rate of grain growth.
2. The presence of foreign particles _____
a) increases recrystallization temperature
b) improves surface hardness of the specimen
c) retards the grain boundary motion
d) softens the specimen
Answer: c
Explanation: Solute atoms in solid solution can form grain boundary atmospheres, the presence of which retards the normal surface-tension induced boundary motion. In order for the boundary to move, it must carry its atmosphere along with it.
3. _____ lowers the retarding effect of the solute/foreign atoms.
a) Increase in temperature
b) Decrease in temperature
c) Increase in amount of solute atoms
d) Decrease in size of solute atoms
Answer: a
Explanation: An increase in temperature lowers the retarding effect of the solute atoms and grain growth occurs under conditions more closely resembling the growth of soap cells.
4. At the high temperatures normally associated with annealing, _____
a) grooves may form on the surface
b) irregularity in surface roughness may occur
c) unwanted bump may form
d) decrease in yield strength may occur
Answer: a
Explanation: At the high temperatures normally associated with annealing, grooves may form on the surfaces where grain boundaries intersect the specimen surface.
5. Grain-boundary grooves are important in grain growth because of _____
a) they can counter the unwanted surface irregularities
b) they improve surface finish
c) they tend to fix the ends of grain boundaries
d) they are the result of perfect recrystallization process
Answer: c
Explanation: Grain-boundary grooves are important in grain growth because they tend to anchor the ends of the grain boundaries , especially if the boundaries are nearly normal to the surface.
6. Thermal grooving has little effect on the overall rate of growth when ______
a) average grain size of the specimen is very small as compared to the size of the specimen
b) average grain size of the specimen is larger as compared to the size of the specimen
c) temperature of the specimen is lower than recrystallization temperature
d) specimen has a high thermal conductivity
Answer: a
Explanation: When the average grain size of a metal specimen is very small compared to the dimensions of the specimen, thermal grooving, or the lack of curvature in the surface grains, has little effect on the overall rate of growth. However, when the grain size approaches the dimensions of the thickness of the specimen, it can be expected that grain-growth rates will be decreased.
7. During normal grain growth, the moving boundaries will be attached to the particles, so that _____
a) the particles exert a pulling force on the boundary
b) the particles exert a pushing force on the boundary
c) grain growth occurs at higher rate
d) surface structure does not get disturbed
Answer: a
Explanation: The moving boundaries will be attached to the particles so that the particles exert a pulling force on the boundary restricting its motion. The boundary will be attached to the particle along the length. If the boundary intersects the particle surface at 90 degrees, the particle will feel a pull of force.
8. The stabilization of fine grain size during heating at high temperatures requires _____
a) a large volume fraction of very small particles
b) a large volume fraction of bigger particles
c) planner grains
d) small grain boundaries
Answer: a
Explanation: The stabilization of fine grain size during heating at high temperatures requires a large volume fraction of very small particles. If the temperature is too high, the particles tend to coarsen or dissolve. When this occurs, some boundaries can break away before the others and abnormal grain growth occurs, transforming the fine-grain array into a very coarse-grain structure.
9. Metal grain boundaries differ from soap films.
a) True
b) False
Answer: a
Explanation: Metal grain boundaries differ from soap films for they possess only a single surface, whereas the latter has 2 surfaces. The driving force per unit area for grain boundary movement can be written in the following manner:
f = ϒ/R
Where f is the force per unit area, ϒ the surface tension of the grain boundary, and R the net radius of curvature of the boundary.
10. Specimen geometry has no part in controlling the rate of grain growth.
a) True
b) False
Answer: b
Explanation: Specimen geometry may play a part in controlling the rate of grain growth. Grain boundaries near any free surfaces of a metal specimen tend to lie perpendicular to the specimen surface. This means that the curvature becomes cylindrical rather than spherical and, in general, cylindrical surfaces move at a slower rate than spherical surfaces with the same radius of curvature.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Annealing – 11”.
1. For which of the following purposes, annealing is not done?
a) Homogenization
b) Recrystallization
c) Stress relieving
d) Decreasing brittleness
Answer: d
Explanation: Annealing refers to a wide group of heat treatment processes and is performed primarily for homogenization, recrystallization or relief of residual stress in typical cold worked or welded components.
2. Depending upon the ______ under which it is performed, annealing eliminates chemical or physical non-homogeneity.
a) humidity conditions
b) temperature conditions
c) time
d) weight of the component
Answer: b
Explanation: Depending upon the temperature conditions under which it is performed, annealing eliminates chemical or physical non-homogeneity produced of phase transformations.
3. How many types of annealing are there?
a) 3
b) 4
c) 5
d) 6
Answer: c
Explanation: Few important variants of annealing are;
• full annealing
• isothermal annealing
• spheroidise annealing
• recrystallization annealing
• stress relief annealing.
4. In case of full annealing of hypo-eutectoid steels, it is heated to a temperature _____
a) above upper critical temperature
b) above lower critical temperature
c) to a critical temperature
d) recrystallization temperature
Answer: a
Explanation: The steel component to above upper critical temperature of ferrite for hypoeutectoid steels and above lower critical temperature for hypereutectoid steels by 30-50⁰C.
5. During full annealing of steel, the component needs to be held above lower or higher critical temperature for _____ per cm of the thickness.
a) 5 min
b) 13 min
c) 20 min
d) 25 min
Answer: c
Explanation: The steel component to above upper critical temperature for a definite holding period of at least 20 minutes per cm of the thick section to assure equalization of temperature throughout the cross-section of the component and complete austenization.
6. In the final stage of full annealing, a steel component is cooled _____
a) rapidly using jet of water
b) using blast of liquid which a mixture of water and some anti-corrosion powder
c) slowly in the furnace
d) slowly in air
Answer: c
Explanation: The final step in the full annealing of steel, is to cool the hot steel component to room temperature slowly in the furnace, which is also called furnace cooling. Rapid cooling is done in the quenching process.
7. The full annealing is used to _____
a) increase the hardness
b) to decrease ductility
c) to refine the grain structure
d) to decrease machinability
Answer: c
Explanation: The full annealing is used to relieve the internal stresses induced due to cold working, welding, etc., to reduce hardness and increase ductility, to refine the grain structure, to make the material homogenous in respect of chemical composition, to increase the uniformity of phase distribution, and to increase machinability.
8. Iso thermal annealing is done in _____ steps.
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: Isothermal annealing consists of four steps. The first step is heating the steel components similar as in the case of full annealing. The second step is slightly fast cooling from the usual austenitizing temperature to a constant temperature just below A1. The third step is to hold at this reduced temperature for sufficient soaking period for the completion of transformation and the final step involves cooling the steel component to room temperature in air.
9. Isothermal annealing requires less time than that for full annealing.
a) True
b) False
Answer: a
Explanation: Due to isothermal annealing, the annealing time is reduced especially for alloy steels which need very slow cooling to obtain the required reduction in hardness by the full annealing. Also, more homogeneity in a structure is obtained as the transformation occurs at the same time throughout the cross section.
10. Isothermal annealing is primarily used for _____
a) high carbon steels
b) low carbon steels
c) aluminium alloy
d) hastelloy
Answer: a
Explanation: Isothermal annealing is primarily used for medium carbon, high carbon and some of the alloy steels. Due to this Improved machinability and surface finish is obtained after machining as compared to that of the full annealed components.
This set of Tough Manufacturing Processes Questions and Answers focuses on “Annealing – 12”.
1. In thermal cycling stage of spheroidised annealing transforms _____ to ______
a) austenite to perlite
b) cementite to carbide
c) cementite from perlite to spheroidal
d) cementite from ferrite to spheroidal
Answer: c
Explanation: In this stage, the thermal cycling in the narrow temperature range around lower critical temperature transforms cementite lamellae from pearlite to spheroidal. During heating above lower critical temperature, cementite or carbides try to dissolve and during cooling they try to re-form. This repeated action spheroidises the carbide particles.
2. Spheroidised annealing is used for ______
a) medium carbon steel
b) hardened alloy steels
c) tool steel
d) stainless steel
Answer: b
Explanation: Spheroidised structures are softer than the fully annealed structures and have excellent machinability. This heat treatment is utilized to high carbon and air hardened alloy steels to soften them and to increase machinability and to reduce the decarburization while hardening of thin sections such as safety razor blades and needles.
3. In recrystallization annealing process, steel component is heated at the temperature in the range______
a) 300⁰C to 400⁰C
b) 455⁰C to 540⁰C
c) 590⁰C to 660⁰C
d) 625⁰C to 675⁰C
Answer: d
Explanation: Recrystallization annealing process consists of heating a steel component below lower critical temperature i.e. at temperature between 625⁰C and 675⁰C , holding at this temperature and subsequent cooling.
4. Recrystallization annealing is applied before _____
a) hot working
b) cold working
c) stress relieving
d) full annealing
Answer: b
Explanation: This type of annealing is applied either before cold working or as an intermediate operation to remove strain hardening between multistep cold working operations. In certain case, recrystallization annealing may also be applied as final heat treatment.
5. Recrystallization annealing _____
a) improves ductility
b) improves hardness
c) decreases surface strain
d) decreases strength
Answer: a
Explanation: Recrystallization annealing relieves the internal stresses in the cold worked steels and weldments and improves the ductility and softness of the steel. Refinement in grain size is also possible by the control of the degree of cold work prior to annealing or by control of annealing temperature and time.
6. In stress relief annealing, steel is heated to a temperature between ______
a) 200⁰C to 250⁰C
b) 300⁰C to 325⁰C
c) 385⁰C to 440⁰C
d) 500⁰C to 550⁰C
Answer: d
Explanation: Stress relief annealing process consists of three steps. In the first step, the cold worked steel is heated to a temperature between 500⁰C to 550⁰C i.e., below recrystallization temperature. The second step involves holding the steel component at this temperature for1-2 hours. The final step is to cool the steel component to room temperature in air.
7. Stress relief annealing _____
a) decreases corrosion resistance
b) relieves stress at the loss of strength
c) improves corrosion resistance
d) improves yield strength
Answer: c
Explanation: The stress relief annealing partly relieves the internal stress in cold worked steels without loss of strength and hardness i.e. without a change in the microstructure. It reduces the risk of distortion while machining and increases corrosion resistance.
8. Stress relief annealing is applicable for _____
a) hypoeutectoid steel containing less than 0.4% carbon
b) hypoeutectoid steel containing less than 1% carbon
c) hypereutectoid steel containing less than 0.4% carbon
d) high speed tool steel
Answer: a
Explanation: Since only low carbon steels can be cold worked, the process is applicable to hypoeutectoid steels containing less than 0.4% carbon. This annealing process is also used on components to relieve internal stresses developed from rapid cooling and phase changes.
9. Spheroidal annealing produces globules of carbide in ferrite.
a) True
b) False
Answer: a
Explanation: Spheroidised annealing is one of the variants of the annealing process that produces typical microstructure consisting of the globules of cementite or carbides in the matrix of ferrite.
10. Holding the steel component at just below the lower critical temperature transforms the _____ to globular cementite particles.
a) perlite
b) austenite
c) martensite
d) lignite
Answer: a
Explanation: Holding the steel component at just below the lower critical temperature transforms the pearlite to globular cementite particles. But this process is very slow and requires more time for obtaining spheroidised structure.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Normalizing & Tempering”.
1. In normalizing of hypoeutectoid steel, the component is heated to a temperature above _____
a) 535⁰C
b) 610⁰C
c) 800⁰C
d) 910⁰C
Answer: d
Explanation: Normalizing process consists of three steps. The first step involves heating the steel component above the 910⁰C temperature for hypoeutectoid steels and above Acm temperature for hypereutectoid steels by 30⁰C to 50⁰C.
2. In normalizing, components are cooled _____
a) using water
b) using oil
c) in still air
d) in furnace
Answer: c
Explanation: The final step in normalizing involves cooling the hot steel component to room temperature in still air. Due to air cooling, normalized components show a slightly different structure and properties than annealed components.
3. Normalizing is used for _____
a) alloy steels
b) high carbon steels
c) tool steels
d) aluminium alloys
Answer: b
Explanation: Normalizing is used for high-carbon steels to eliminate the cementite network that may develop upon slow cooling in the temperature range from point Acm to point A1 .
4. Normalizing is not used for relieve internal stresses by which of the following processes?
a) Casting
b) Drilling
c) Welding
d) Forming
Answer: b
Explanation: Normalizing is also used to relieve internal stresses induced by heat treating, welding, casting, forging, forming, or machining. Normalizing also improves the ductility without reducing the hardness and strength.
5. Martensite obtained after hardening is extremely _______
a) hard
b) ductile
c) brittle
d) soft
Answer: c
Explanation: The hardened steel is not readily suitable for engineering applications. It possesses few drawbacks, which are as follows:
• martensite obtained after hardening is extremely brittle and will result in failure of engineering components by cracking
• Formation of martensite from austenite by quenching produces high internal stresses in the hardened steel.
6. Structures obtained after hardening consists of _______
a) martensite
b) cementite
c) perlite
d) carbon
Answer: a
Explanation: Structures obtained after hardening consists of martensite and retained austenite. Both these phases are metastable and will change to stable phases with time which subsequently results in a change in dimensions and properties of the steel in service.
7. Tempering is achieved by heating hardened steel to a temperature in the range of ______
a) 100⁰C – 150⁰C
b) 100⁰C – 680⁰C
c) 200⁰C – 375⁰C
d) 300⁰C – 835⁰C
Answer: b
Explanation: Tempering is achieved by heating hardened steel to a temperature below lower critical temperature, which is in the range of 100⁰C – 680⁰C, hold the component at this temperature for a soaking period of 1 to 2 hours , and subsequently cooling back to room temperature.
8. Highly alloyed tool steels are tempered in the range of ______
a) 100⁰C – 190⁰C
b) 180⁰C – 300⁰C
c) 450⁰C – 620⁰C
d) 500⁰C – 600⁰C
Answer: d
Explanation: The tempering temperature is decided based on the type of steel. Highly alloyed tool steels are tempered in the range of 500⁰C – 600⁰C. Low alloy steels are tempered above 400⁰C to get a good combination of strength and ductility. Spring steels are tempered between 300⁰C – 400⁰C.
9. Increase in the tempering temperature ______
a) increases hardness
b) increases ductility
c) decreases conductivity
d) increases toughness
Answer: d
Explanation: It is observed that the increase in the tempering temperature decreases the hardness and internal stresses while increases the toughness. But after a particular temperature, there is no significant change in hardness and toughness.
10. Normalizing takes less time than that for annealing.
a) True
b) False
Answer: a
Explanation: The properties of normalized components are not much different from those of annealed components. However, normalizing takes less time and is more convenient and economical than annealing and hence is a more common heat treatment in industries.
11. Perlite formed during normalising is coarse in nature.
a) True
b) False
Answer: b
Explanation: Pearlite formed during normalizing is fine and usually appears unresolved with an optical microscope. Whereas, pearlite during annealing is coarse and usually gets resolved by the optical microscope.
12. In normalizing, grain size distribution ______
a) is uniform
b) is less uniform
c) varies directly with temperature
d) varies with time
Answer: b
Explanation: If we compare annealing and normalizing, the following point can be made:
In annealing,
• Grain size distribution is more uniform
• Internal stresses are least
• Less hardness, tensile strength and toughness
In normalizing,
• Grain size distribution is slightly less uniform
• Internal stresses are slightly more
• Slightly more hardness, tensile strength and toughness.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Hardening – 1”.
1. How many types of hardening techniques are there?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: Different techniques to improve the hardness of the steels are as follows:
• conventional hardening
• martempering
• austempering.
2. In a conventional hardening of hypereutectoid steels, the component is heated above _____
a) 228⁰C
b) 363⁰C
c) 585⁰C
d) 738⁰C
Answer: d
Explanation: The first step in hardening involves heating the steel to above 910⁰C for hypoeutectoid steels and above 738⁰C for hypereutectoid steels by approximately 50⁰C.
3. After hardening, the component is cooled ______
a) at the critical cooling rate
b) at the rate just more than the critical cooling rate
c) in still air
d) at rate at which it was heated
Answer: b
Explanation: After austenization, the next step in hardening involves cooling of hot steel components at a rate just exceeding the critical cooling rate of the steel to room temperature or below room temperature.
4. In conventional hardening _______ transforms to _______
a) austenite, martensite
b) cementite, martensite
c) perlite, α-iron
d) austenite, ferrite
Answer: a
Explanation: In this conventional hardening process, the austenite transforms to martensite. The final step in the hardening process is the tempering of the martensite to achieve the desired hardness. This martensite structure improves the hardness of the component.
5. Martempering uses _______ quenching.
a) water
b) oil
c) brine
d) interrupted
Answer: d
Explanation: Martempering process overcomes the limitation of the conventional hardening process. This process follows interrupted quenching operation. In other words, the cooling is stopped at a point above the martensite transformation region to allow sufficient time for the centre to cool to the temperature as the surface. Further cooling is continued through the martensite region, followed by the usual tempering.
6. Austempering is used to overcome the limitations of ______
a) martempering
b) conventional hardening
c) quenching
d) annealing
Answer: b
Explanation: This process is also used to overcome the limitation of the conventional hardening process. Here the quench is interrupted at a higher temperature than for martempering to allow the metal at the centre of the part to reach the same temperature as the surface.
7. During austempering, steel is transformed to ______
a) bainite
b) bauxite
c) α-ferrite
d) α-martensite
Answer: a
Explanation: In austempering, both the centre and surface are allowed to transform to bainite and are then cooled to room temperature. Austempering causes less distortion and cracking than that in the case of martempering.
8. Austempering improves ______
a) corrosion resistance
b) toughness
c) hardness
d) tensile strength
Answer: b
Explanation: Austempering improves the impact toughness and the ductility of the metal than that in the case of martempering and conventional hardening. It also avoids the tempering operation.
9. Alloy steels can be hardened by simple air cooling.
a) True
b) False
Answer: a
Explanation: Alloy steels have less critical cooling rate and hence some of the alloy steels can be hardened by simple air cooling. Proper quenching medium should be used such that the component gets cooled at a rate just exceeding the critical cooling rate of that steel.
10. High carbon steels are hardened by oil quenching.
a) True
b) False
Answer: a
Explanation: High carbon steels have slightly more critical cooling rate and has to be hardened by oil quenching. Medium carbon steels have still higher critical cooling rates and hence water or brine quenching is necessary.
This set of Manufacturing Processes Questions & Answers for Exams focuses on “Hardening – 2”.
1. How many types of hardening processes are commonly used?
a) 3
b) 5
c) 6
d) 7
Answer: b
Explanation: There are several other ways the strength or the hardness of the surface can be increased without adversely affecting the toughness of the core. Some of the most common techniques are as follows:
• Induction hardening
• Case carburizing + case hardening
• Nitriding
• Shot peening
• Hard facing, coating or surface alloying.
2. Which of the following is not the purpose of the surface hardening?
a) To improve wear resistance
b) To increase fatigue life
c) Prevention from cracking
d) To improve ductility
Answer: d
Explanation: The purpose of surface hardening is to develop a hard surface with compressive residual stress, to improve its wear resistance, to increase its fatigue life and to avoid susceptibility to distortion and cracking.
3. How many surface hardening methods are there which are commonly used?
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: The most commonly used methods of surface hardening are as follows:
• Shot peening: general applicable to all metals
• Coating / hard facing
• Surface heating & cooling: steel
• Surface diffusion & subsequent treatment.
4. Shot peening technique is applicable to all metals and alloys that are prone to _____
a) plastic deformation
b) brittle failure
c) fatigue failure
d) ductile deformation
Answer: a
Explanation: Shot peening technique is applicable to all metals and alloys that are amenable to plastic deformation. The part to be hardened is placed in a chamber where extremely fine hard particles moving at a high speed keep striking at its surface. The energy of the moving particles is high enough to cause local plastic deformation at its surface.
5. Which of the following is not subjected to shot peening?
a) Landing gears of an aircraft
b) Automotive gears
c) Shafts
d) Coil springs
Answer: c
Explanation: BLanding gears of aircraft are subjected to shot peening to develop residual compressive stress on its surface. Even automotive gears, following carburizing, are subjected to hot peening to raise the value of compressive residual stress (to as high as 1000 – 1200 MPa particularly at depths of 30 – 40 microns. This help resist crack propagation during service as result of fatigue loading.
6. Which of the following is not the outcome of hard facing?
a) Improved resistance to particle erosion
b) Improved resistance to abrasion
c) Improved resistance to fretting
d) Improved resistance to plastic deformation
Answer: d
Explanation: Engineering components that are required to resist solid particle erosion, abrasion, fretting orcavitation are usually given a hard surface coating. This consists of a fine dispersion of hard metal carbides in a compatible metal matrix. Thermal spray is the most commonly used technique to apply such coatings on the component.
7. Which of the following is the most commonly used coating materials for hard facing?
a) Mixture of chromium carbide and cobalt
b) Mixture of calcium nitrate and iron carbide
c) Mixture of copper oxide and zinc oxide
d) Mixture of boron carbide and vanadium pentoxide
Answer: a
Explanation: The most commonly used coating materials are mixtures of chromium or tungsten carbides in either cobalt or nickel-chromium alloy matrix. Hard facing is also a commonly used technique to salvage worn out parts so that they could be reused.
8. Induction hardening is used for _____
a) steels
b) aluminium alloys
c) copper alloys
d) zinc alloys
Answer: a
Explanation: This is applicable only for steel. An induction coil is used to heat the component to be hardened. Only the surface gets heated. Its microstructure transforms into austenite from a mixture of ferrite and cementite, but the structure of the core remains intact as it remains cold all through the process.
9. During induction hardening, the microstructure of the surface gets transformed into _____
a) austenite
b) perlite
c) bainite
d) martensite
Answer: d
Explanation: Once the process is complete the microstructure of the surface gets transformed into martensite while that at its core remains unaltered. Hardness of induction hardened steel component may often be higher than that in through hardened steel having identical composition. One of the main advantages of induction hardening is good surface finish and little distortion.
10. Which of following is not the feature of induction hardening?
a) Heat the surface to a temperature above an austenitic region
b) Good surface finish
c) Fast heating & short hold time
d) Applicable to carbon steels having
Answer: d
Explanation: The salient features of induction hardening are as follows:
• Heat the surface to a temperature above austenitic region
• Core does not get heated: the structure remains unaltered
• Surface converts to martensite on quenching.
• Fast heating & short hold time: needs higher austenization temperature
• Martensite forms in fine inhomogeneous grains of austenite
• Applicable to carbon steels
• Little distortion & good surface finish.
11. The hardness of steel depends only on the ______
a) carbon content
b) temperature
c) yield strength
d) tensile strength
Answer: a
Explanation: The hardness of steel depends only on the concentration of carbon in steel. Therefore it may be enough to have high carbon only at the surface. This can be achieved by increasing the concentration of carbon in a component made of low carbon steel by allowing carbon to diffuse into it.
12. A major limitation of pack carburizing is poor control over_____
a) temperature
b) ductility
c) hardness
d) strength
Answer: a
Explanation: A major limitation of pack carburizing is poor control over temperature & carburization depth. On completion of the process, the steel parts are cooled slowly. Direct quenching is not possible as the job is surrounded by carburizing mixture packed in a sealed box having high thermal mass. This can be overcome by using a gaseous or liquid carburizing medium.
13. Which of the following is most commonly used as carburizing gas?
a) CH 4
b) CO
c) N 2
d) C 2 H 2
Answer: a
Explanation: CH 4 and CO are the most commonly used carburizing gas. It is usually mixed with decarburizing (H 2 and CO 2 ) and neutral gases (N 2 ). This helps maintain close control over carbon potential. Gas carburization is done by keeping the samples at the carburizing temperature for a specified time in a furnace having a mixture of carburizing and neutral gas.
14. The main purpose of this stage is to harden the case consisting of austenite and globules of un‐dissolved carbide.
a) True
b) False
Answer: a
Explanation: The main purpose of case hardening is to harden the case. Therefore the component after case refining is heated to 30⁰C-40⁰C above the lower critical temperature. At this temperature, the case consists of austenite and globules of undissolved carbide. The structure of the core during this stage of heat treatment should have ferrite and austenite.
15. The reasons for case hardening is to develop compressive residual stress.
a) True
b) False
Answer: a
Explanation: One of the main reasons for case hardening is to develop compressive residual stress at the surface of the components that are subjected to fatigue loading. A general thumb rule is that the region that transforms last has a compressive stress. In the case of a carburized steel there is a large difference in the concentration of carbon at the surface and that at the centre. The difference is of large that although the surfaced on quenching cools faster it transforms to martensite later than the core. Since it transforms last it should be under compression. This is the reason why case hardened components have compressive residual stress.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “Quenching”.
1. Quenching is the process of _______
a) rapid cooling
b) slow cooling
c) rapid heating
d) slow heating
Answer: a
Explanation: Quenching is the process of rapidly cooling material from high temperature. This rapid cooling is achieved using quenching media. Quenching is done during the hardening process.
2. Quenching medium is decided on the basis of ______
a) weight of the specimen
b) material of the specimen
c) thickness of the specimen
d) application of the specimen
Answer: c
Explanation: The thickness of the material to be quenched along with the rate of cooling required helps to choose the quenching medium. The quenching medium has to be chosen carefully.
3. How many types of quenching are there?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: There are many different types of quenching:
• quenching in a fine vapour or mist is known as fog quenching
• if quenching is carried out directly from some other heat treatment operation , it is known as direct quenching
• if only some portions of a workpiece are quenched, it is known as selective quenching.
4. An alloy quenched past the nose of the C-curve in the isothermal transformation diagram will undergo _______ transformation.
a) martensitic
b) perlitic
c) austentic
d) ferritic
Answer: a
Explanation: The most common example of quenching is what is used in steels; an alloy quenched past the nose of the C-curve in the isothermal transformation diagram will undergo a martensitic transformation, which will lead to high hardness in the material.
5. Quenching is can also be used for _____
a) fibres
b) polymers
c) metallic glasses
d) plastics
Answer: c
Explanation: Quenching can also be possible to rapidly quench molten metallic liquids to retain the liquid-like structure; such materials are commonly known as metallic glasses. Quenching is also a method used to determine hardenability of materials.
6. Quenching is generally carried out to _____
a) remove brittleness
b) remove rust
c) freeze the high temperature structure
d) oxidise the surface of the component for good reason
Answer: c
Explanation: Quenching is generally carried out to freeze the high temperature structure or phase in the material; however, it is not always possible for the structure to be retained.
7. The heat transfer during quenching is related to heat transfer during ______
a) annealing
b) boiling
c) martempering
d) hardening
Answer: b
Explanation: The heat transfer during quenching is very closely related to heat transfer during boiling; and, boiling is a very complicated phenomenon as far as the energy transport is considered.
8. If a quenching medium cools slower than the required rate, the final product will have different properties than desired.
a) True
b) False
Answer: a
Explanation: If a quenching medium that cools slower than the required rate is chosen, the quench is not effective in producing the required microstructures and hence properties.
9. If the quenching medium cools the specimen at a faster rate, cracks might occur in the specimen.
a) True
b) False
Answer: a
Explanation: If a quenching medium that cools faster than the required rate is used, then that can sometimes lead to defects such as warping and cracking. Therefore special care should be taken while selecting the quenching medium.
10. During quenching, there could be a mechanism like ______
a) vacancy diffusion
b) vacancy formation
c) grain diffusion
d) grain boundary distortion
Answer: a
Explanation: During quenching, there could be mechanisms such as vacancies diffusing to the grain boundaries leading to PFZs that become operative.
This set of Manufacturing Processes Multiple Choice Questions & Answers focuses on “CNC Machining”.
1. In machining of a workpiece, the material is removed by_____
a) drilling action
b) melting action
c) shearing acting
d) using brittleness of the material
Answer: c
Explanation: There are different machining processes, such as turning, milling, boring etc. In all these cases metal is removed by a shearing process, which occurs due to the relative motion between the workpiece and the tool. Generally, one of the two rotates at designated and generally high speed, causing the shearing of material , from the workpiece. The other moves relatively slowly to effect removal of metal throughout the workpiece.
2. The depth that the tool is plunged into the surface is called as ______
a) feed
b) depth of cut
c) depth of tool
d) working depth
Answer: b
Explanation: The depth of cut, DOC is the depth that the tool is plunged into the surface. Feed defines the relative lateral movement between the cutting tool and the workpiece. Thus, together with the depth of cut, feed decides the cross section of the material removed for every rotation of the job or the tool.
3. Feed is measured in units of _____
a) length/revolution
b) degree/revolution
c) length
d) velocity
Answer: a
Explanation: Feed is the amount of material removed for each revolution or per pass of the tool over the workpiece and is measured in units of length/revolution, length/pass or other appropriate units for the particular process.
4. CNC machining centres do not include operations like ______
a) milling
b) boring
c) welding
d) tapping
Answer: c
Explanation: CNC machining centres are developed for machining prismatic components combining operations like milling, drilling, boring and tapping. Gradually machines for manufacturing cylindrical components, called turning centres are also developed.
5. In CNC systems multiple microprocessors and programmable logic controllers work ______
a) in parallel
b) in series
c) one after the other
d) for 80% of the total machining time
Answer: a
Explanation: In CNC systems multiple microprocessors and programmable logic controllers work in parallel for simultaneous servo position and velocity control of several axes of a machine for contour cutting as well as monitoring of the cutting process and the machine tool.
6. Which of the following is not the advantage of CNC machines?
a) Higher flexibility
b) Improved quality
c) Reduced scrap rate
d) Improved strength of the components
Answer: d
Explanation: CNC machines offer the following advantages in manufacturing:
• Higher flexibility
• Increased productivity
• Improved quality
• Reduced scrap rate
• Reliable and Safe operation
• Smaller footprint.
7. In how many ways CNC machine tool systems can be classified?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: CNC machine tool systems can be classified in various ways such as:
• Point-to-point or contouring: depending on whether the machine cuts metal while the workpiece moves relative to the tool
• Incremental or absolute: depending on the type of coordinate system adopted to parameterise the motion commands
• Open-loop or closed-loop: depending on the control system adopted for axis motion control.
8. Point-to-point systems are used for _____
a) reaming
b) parting
c) grooving
d) facing
Answer: a
Explanation: Such systems are used, typically, to perform hole operations such as drilling, boring, reaming, tapping and punching. In a PTP system, the path of the cutting tool and its feed rate while traveling from one point to the next are not significant, since, the tool is not cutting while there is motion.
9. In part programming, interpolation is used for obtaining _______ trajectory.
a) helicoidal
b) pentagonal
c) triangular
d) zig-zag
Answer: a
Explanation: Interpolation consists of the calculation of the coordinated movement of several axes using the programmed parameters, in order to obtain a resulting trajectory, which can be of various types, such as:
– Straight line
– Circular
– Helicoidal.
10. For CNC machining skilled part programmers are needed.
a) True
b) False
Answer: a
Explanation: The main disadvantages of NC systems are:
• Relatively higher cost compared to manual versions
• More complicated maintenance due to the complex nature of the technologies
• Need for skilled part programmers.
11. An absolute NC system is one in which all position coordinates are referred to one fixed origin called the zero point.
a) True
b) False
Answer: a
Explanation: An absolute NC system is one in which all position coordinates are referred to one fixed origin called the zero point. The zero point may be defined at any suitable point within the limits of the machine tool table and can be redefined from time to time.
