Category: Manufacturing Engineering Objective Questions

Manufacturing Processes Multiple Choice Questions on “Electrochemical Etching – 7”.

1. Morphology of μpSi and mpSi can be defined by a concrete spatial distribution.
a) True
b) False
Answer: b
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 (J) is the most critical factor.
a) True
b) False
Answer: a
Clarification: The growth of well-defined cylindrical macropores from top to bottom in MpSi can be precisely controlled through the etching parameters (e.g. etching current density, HF concentration and its temperature, wafer doping, illumination intensity, etc.). In particular, among these parameters, the etching current density (J) is a critical factor to lead a homogeneous pore growth as the longer the pore the more effective the collection of photo-generated holes.

Manufacturing Processes Multiple Choice Questions on “Abrasive Jet Micromachining – 3”.

1. In AJMM, material removal starts when the fracture strength is reached.
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: The mass loss of workpiece is proportional to the amount of abrasive.
Mass loss = (Kρmv²)/(2H), where, K (> 2) 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 (elastomers and some metals) due to time variant erosion behaviour.

4. In AJMM, there is initial weight gain in the workpiece.
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: 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 (PMMA).
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Manufacturing Processes Multiple Choice Questions 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
Clarification: Friction Welding (FRW) 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Manufacturing Processes Multiple Choice Questions on “Annealing – 7”.

1. Polygonization is essentially completed before the start of ______
a) solidification
b) recrystallization
c) cooling
d) grain growth
Answer: b
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 (within a reasonable time period).

5. The critical deformation is not dependent on ______
a) material properties
b) tension
c) torsion
d) compression
Answer: a
Clarification: 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
Clarification: If the grain size of metal is very small (less than ~0.05 mm in diameter), plastic deformation occurs without appreciable roughing of the surface (assuming that deformation does not occur by movement of Lüdersbands).

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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: In metal that is cold-rolled (sheet) or drawn cold through dies (wires, rods, and pipe), it is relatively easy to avoid a critical amount of cold work because the metal is more or less uniformly deformed.

Manufacturing Engineering Multiple Choice Questions on “Mechanical Testing”.

1. Hounsfield tensometer can be used to perform __________
a) Tensile test
b) Compressive test
c) Hardness test
d) Toughness test
Answer: a
Clarification: Hounsfield tensometer, Universal testing machine, Instron and MTS (materials testing system) are the common machine that are used to for tensile test. Hounsfield tensometer is a small machine and widely used for tensile test in research laboratories.

2. ASTM stands for __________
a) American Society for Tensile Measurement
b) American Society for Testing and Materials
c) American Society for Tool Measurement
d) American Society for Tensile Material
Answer: b
Clarification: ASTM stands for American Society for Testing and Materials. ASTM develops technical standards for a wide range of materials products. American Society for Tensile Measurement are used to decide various standard in tensile measurement.

3. According to ASTM standard, which of the following relation is correct about gauge length of cross section area ‘A’?
a) L = 2.51(sqrt{A})
b) L = 4.51(sqrt{A})
c) L = 2(sqrt{A})
d) L = 3.51(sqrt{A})
Answer: b
Clarification: According to ASTM standard, gauge length = 4.51(sqrt{A}).

4. According to BS standard, which of the following relation is correct about gauge length of cross section area ‘A’?
a) L = 2.51(sqrt{A})
b) L = 4.51(sqrt{A})
c) L = 4(sqrt{A})
d) L = 3.51(sqrt{A})
Answer: c
Clarification: According to BS standard, gauge length = 4(sqrt{A}), where A denotes the cross section area of specimen used under testing.

5. According to DIN standard, which of the following relation is correct about gauge length of cross section area ‘A’?
a) L = 12.51(sqrt{A})
b) L = 14.51(sqrt{A})
c) L = 4(sqrt{A})
d) L = 11.2(sqrt{A})
Answer: d
Clarification: According to DIN standard, gauge length=11.2(sqrt{A}), where A denotes the cross section area of specimen used under testing.

6. Mohs hardness test has a scale range of _________
a) 1 to 10
b) 100 to 200
c) 1 to 1000
d) 1 to 3000
Answer: a
Clarification: Mohs hardness scale was developed by “Frederich Mohs” in 1822, which is a chart that denotes relative hardness of the various materials (1-softest to 10-hardenst). According to Mohs scale, diamond is the hardest material and talc is the softest material.

7. Brinell hardness test has a scale range of _________
a) 0 to 10
b) 100 to 200
c) 0 to 1000
d) 0 to 3000
Answer: d
Clarification: Brinell hardness test has a scale range of 0 to 3000. Brinell hardness number of soft irons is ranges from 67 to 500.

8. Rockwell hardness test has a scale range of _________
a) 0 to 10
b) 100 to 200
c) 0 to 1000
d) 0 to 3000
Answer: c
Clarification: Rockwell hardness test has a scale range of 0 to 1000. It is used to measure the hardness of a specimen.

9. Vickers hardness test has a scale range of _____________
a) 0 to 10
b) 100 to 200
c) 0 to 1000
d) 0 to 3000
Answer: d
Clarification: Vickers hardness test has a scale range of 0 to 3000. It is used to measure the hardness of a specimen.

10. Brinell Hardness Number (BHN) for soft iron is between _____________
a) 1000-2000
b) 227-857
c) 67-500
d) 0-10
Answer: c
Clarification: Brinell hardness number (BHN) of soft iron ranges from 67 to 500.