Category: Manufacturing Engineering Objective Questions

Manufacturing Processes Puzzles on “Electrochemical Etching – 10”.

1. Pore formation in μpSi is independent of quantum confinement.
a) True
b) False
Answer: b
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: If the energy barrier in the wall region( as stated in the previous question) 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

To practice all Puzzles on Manufacturing Processes,

Manufacturing Processes Multiple Choice Questions on “Abrasive Jet Micromachining – 6”.

1. Powder flowability is affected by particle size and surface texture.
a) True
b) False
Answer: a
Clarification: 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
Clarification: Inter particle adhesion is further enhanced by moisture that adsorbs readily onto these hygroscopic (having a tendency to absorb moisture) surfaces.

3. Relative humidity can affect adhesive forces.
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 (similar to the tool used for boring earth).

7. In powder feeding systems, powder bridging, compaction, and agglomeration are desirable.
a) True
b) False
Answer: b
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Manufacturing Processes Questions and Answers for Aptitude test 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
Clarification: 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
Clarification: 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
Clarification: 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 (flash trap).

4. Part geometry and accessibility of the flash are the factors which decide flash removal process.
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

Processes for Aptitude test,

Manufacturing Processes Multiple Choice Questions on “Laser Welding – 1”.

1. Laser beam welding is a ______ joining process.
a) fission
b) fusion
c) coherent
d) plastic
Answer: b
Clarification: Laser is an acronym for light amplification by stimulated emission of radiation. Laser Beam Welding (LBW) 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
Clarification: In the LBM process, the laser beam is directed by flat optical elements, such as mirrors and then focused to a small spot (for high power density) 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
Clarification: 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 CO₂ laser
c) 2 µm wavelength CO₂ laser
d) Nd- YAS laser
Answer: b
Clarification: The Lasers which are predominantly being used for industrial material processing and welding tasks are the Nd-YAG laser and 1.06 µm wavelength CO₂ laser, with the active elements most commonly employed in these two varieties of lasers being the neodymium (Nd) ion and the CO₂ 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
Clarification: It utilizes an impurity in a host material as the active medium. Thus, the neodymium ion (Nd+++) 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
Clarification: 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
Clarification: 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) CO₂ lasers
b) Nd-YAG lasers
c) Ruby lasers
d) Dye lasers
Answer: a
Clarification: The electric discharge style CO₂ 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. CO₂ lasers employs gas mixture of _____
a) nitrogen and helium
b) hydrogen and helium
c) argon and xenon
d) oxygen and nitrogen
Answer: a
Clarification: 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
Clarification: 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 CO₂ lasers?
a) 2
b) 3
c) 4
d) 5
Answer: b
Clarification: CO₂ 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 CO₂ lasers.
a) True
b) False
Answer: a
Clarification: They are the simplest of the CO₂ 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 CO₂ lasers can generate laser beams with a constant rating of 80 Watts.
a) True
b) False
Answer: a
Clarification: 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.

Manufacturing Processes Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Grain-boundary grooves are important in grain growth because they tend to anchor the ends of the grain boundaries (where they meet the surface), 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 (∆pin the analogous soap bubble case) can be written in the following manner:
f = (2ϒ)/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
Clarification: 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.