Category: Manufacturing Engineering Objective Questions

250+ TOP MCQs on Fluid Flow and Heat Transfer and Answers

Manufacturing Engineering Multiple Choice Questions on “Fluid Flow and Heat Transfer”.

1. The flow of fluid which is highly chaotic is called as?
a) Laminar
b) Turbulence
c) Reynolds
d) Irrotational flow
Answer: b
Clarification: Turbulent flow is chaotic. However, not all chaotic flows are turbulent. Turbulent flow is characterized by the irregular movement of particles of the fluid. In contrast to laminar the fluid does not flow in parallel layers, the lateral mixing is very high, and there is a disruption between the layers. Turbulence is also characterized by recirculation, eddies, and apparent randomness, in other sense, in turbulent flow-the speed of the fluid at a point is continuously undergoing changes in both magnitude and direction.

2. The capability of molten metal to fill mold cavities is called ____________
a) viscosity
b) fluidity
c) turbulence
d) velocity
Answer: b
Clarification: Fluidity is the property of a fluid which allows fluid to flow. In general understanding, one can say, the fluidity is inversely proportional to viscosity. Factors affecting fluidity in casting are as follows.
i. Modulus: fluidity length increases as the modulus (volume/surface area) of the casting increases
ii. Section thickness: larger thickness of section results in higher fluidity
iii. Heat transfer coefficient: a reduction in the rate of heat transfer will increase fluidity
iv. Superheating: the temperature increment above the melting point increases fluidity
v. Mould temperature: higher mould temperature increases fluidity
vi. Pouring rate: lower pouring rates decrease fluidity because of larger cooling.

3. The liquid metal reduces its fluidity mainly due to?
a) high viscosity
b) high friction factor
c) high surface tension
d) high turbulence
Answer: c
Clarification: A high surface tension of the liquid metal reduces fluidity. Because of this, oxide films on the surface of the molten metal have a significant adverse effect on fluidity.

4. The slower the rate of pouring molten metal into the mold, the nature of fluidity will be?
a) lower
b) higher
c) constant
d) either higher or lower
Answer: a
Clarification: The slower the rate of pouring molten metal into the mold, the lower is the fluidity because of the higher rate of cooling when poured slowly.

5. With an increase in the thickness of insulation around a circular pipe, heat loss to surrounding due to ____________
a) convection increase, while that the due to conduction decreases
b) convection decrease, while that due to conduction increases
c) convection and conduction decreases
d) convection and conduction increases
Answer: b
Clarification: By increasing the thickness of insulation, the convection heat transfer co-efficient decreases and heat loss by the convection also decreases. These both cases are limited for the critical thickness of insulation.

6. For a given heat flow and for the same thickness, the temperature drop across the material will be maximum for ____________
a) copper
b) steel
c) glass-wool
d) refractory brick
Answer: c
Clarification: Q = -kA (dT/dx)
Qdx/A = -kdT
therefore, kdT = constant or dT ∞ 1/k.

7. In descending order of magnitude, the thermal conductivity of:
i. Pure iron,
ii. Liquid water,
iii. Saturated water vapour, and
iv. Pure aluminium
can be arranged as?
a) (i), (ii), (iii) and (iv)
b) (ii), (iii), (i) and (iv)
c) (iv), (i), (ii) and (iii)
d) (iv), (iii), (ii) and (i)
Answer: c
Clarification: Thermal conductivity of values at room temperature are tabulated below:

S.No. Material Thermal Conductivity (W/m-K)
1 Iron 79.5
2 Water 0.6
3 Water vapour 0.025
4 Aluminium 150

8. A copper block and an air mass block having similar dimensions are subjected to symmetrical heat transfer from one face of each block. The other face of the block will be reaching the same temperature at a rate is?
a) Faster in air block
b) Faster in copper block
c) Equal in air as well as copper block
d) Cannot be predicted with the given information
Answer: b
Clarification: Copper has a thermal conductivity of 400 W/m-K and air has an value of 0.026 W/m-K.

9. Consider the following statements:
The Fourier heat conduction equation Q = -kA(dT/dx) presumes
i. Steady-state conditions
ii. Constant value of thermal conductivity.
iii. Uniform temperatures at the wall surfaces
iv. One-dimensional heat flow.
Which of the above statements are correct?
a) (i), (ii) and (iii) are correct
b) (i), (ii) and (iv) are correct
c) (ii), (iii) and (iv) are correct
d) (i), (iii) and (iv) are correct
Answer: d
Clarification: Thermal conductivity may constant or variable.

10. The outer surface of a long cylinder is maintained at constant temperature. The cylinder does not have any heat source. The temperature in the cylinder will?
a) Increase linearly with radius
b) Decrease linearly with radius
c) Be independent of radius
d) Vary logarithmically with radius
Answer: d
Clarification: In case of cylinder, in Q = -kA (dT/dr), thus indicating the logarithmic change.

11. For conduction through a spherical wall with constant thermal conductivity and with inner side temperature greater than outer wall temperature, (one dimensional heat transfer), what is the type of temperature distribution?
a) Linear
b) Parabolic
c) Hyperbolic
d) Logarithmic
Answer: c
Clarification: Temp distribution would be t – t1.

250+ TOP MCQs on Electrochemical Grinding and Answers

Manufacturing Processes Multiple Choice Questions on “Electrochemical Grinding”.

1. In electro-chemical grinding, grinding wheel is used as a cathode.
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: 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 (ECM), ECG consumes less power.
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Applications of ECG are as follows;
(1) Single largest use for ECG is in the manufacturing and remanufacturing of turbine blades and vanes for aircraft turbine engines
(2) Grinding of tungsten carbide tool inserts
(3) Re-profiling worn locomotive traction motor gears
(4) Burr-free sharpening of hypodermic needles
(5) Grinding of surgical needles, other thin wall tubes, and fragile parts
(6) Machining of fragile or very hard and tough material – honey comb, thin walled tubes and skins
(7) High MRR’s when grinding hard, tough, stringy, work-hardenable or heat sensitive materials.

250+ TOP MCQs on Electrochemical Etching – 12 and Answers

Manufacturing Processes Multiple Choice Questions 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
Clarification: 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
Clarification: The etching direction in metal-assisted etching can be controlled on silicon (100) and non-(100) 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
Clarification: 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
Clarification: 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
Clarification: When a silicon substrate is partly covered by a noble metal and it is immersed in an etchant solution composed of an oxidative agent (e.g. hydrogen peroxide) 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
Clarification: 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
Clarification: 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 H2O2.

8. In metal-assisted etching of pSi, the noble metal works as a cathode.
a) True
b) False
Answer: a
Clarification: 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:
H2O2 + 2H+ -> 2H2O + 2H+
2H+ -> H2 + 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
Clarification: 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
Clarification: 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.

250+ TOP MCQs on Abrasive Jet Micromachining – 8 and Answers

Manufacturing Processes Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 (sensing mass and thick supporting beam).

250+ TOP MCQs on Electron Beam Machining – 2 and Answers

Manufacturing Processes Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: After the apertures, the electron beam passes through the final section of the electromagnetic lens and deflection coil. The electromagnetic lens 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 (if needed)
c) It prevents power losses
d) It prevents vapour generated during machining to reach the gun
Answer: d
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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}.

250+ TOP MCQs on Laser Welding – 3 and Answers

Manufacturing Processes Question Paper 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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/mm2.
a) 101
b) 102
c) 103
d) 104
Answer: d
Clarification: Conduction joining describes a family of processes in which the laser beam is focused:
– To give a power density on the order of 103 W/mm2
– 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
Clarification: 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
Clarification: The first conduction welds were made in the early 1960s, using low power
• pulsed ruby lasers, and
• CO2 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
Clarification: 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
Clarification: 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
– CO2, Nd-YAG and diode lasers with power levels on the order of tens of watts
– Direct heating by a CO2 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
Clarification: Transmission welding is an efficient means of joining polymers that transmit the near infrared radiation of Nd-YAG lasers and diode lasers.

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