300+ REAL TIME Manufacturing Engineering Objective Questions & Answers 2023

250+ TOP MCQs on Electro-Chemical Machining – 5 and Answers

Manufacturing Processes Questions and Answers for Experienced people 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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_iν_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
Clarification: In practise, metal removal rates are often higher than the estimated ones because;
(1) The exact valency at which a metal behaves in the reaction is generally unknown.
(2) 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
Clarification: 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 cm² for copper, 25 cm² bronze and brass, and 250 cm² 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
Clarification: 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.

Manufacturing Processes for Experienced people,

250+ TOP MCQs on Electrochemical Etching – 17 and Answers

Manufacturing Processes Multiple Choice Questions 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
Clarification: As far as the doping type is concerned, the etching rate in n-type silicon is faster than that of p-type silicon for (100) and (111) crystallographic orientations with the same resistivity (i.e. 7–13 Ω cm).

2. The morphology of silicon nanowires produced by metal-assisted etching of silicon changes with the doping level.
a) True
b) False
Answer: a
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: Interference lithography (IL) 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
Clarification: 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
Clarification: 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 (NAA) mask technique is used.
a) True
b) False
Answer: a
Clarification: Another approach used to etch the surface of silicon wafers at specific positions by metal-assisted etching is the use of nanoporous anodic alumina (NAA) masks. Self-ordered NAA is basically a nanoporous matrix based on alumina (aluminium oxide–Al₂O₃) 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
Clarification: NAA is produced by electrochemical anodization of aluminium, which is typically performed in acid electrolytes based on aqueous solutions of sulphuric (H₂SO₄), oxalic (H₂C₂O₄) or phosphoric acids (H₃PO₄).

250+ TOP MCQs on Abrasive Jet Micromachining – 13 and Answers

Manufacturing Processes Multiple Choice Questions 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
Clarification: 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 (keeping all other parameters unchanged) _____
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
Clarification: Assuming no losses, abrasive water jet velocity for a given pressure is calculated by formula; 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
Clarification: In this case, liquid nitrogen replaces the water phase and dry ice crystals (solid CO₂ 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
Clarification: 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
Clarification: The focussing tube is generally made of tungsten carbide (powder metallurgy product) 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
Clarification: 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*(1/(1+R))*V_wj
b) V_awj = η*(1+R)*V_wj
c) V_awj = R*(1/(1+ η))*V_wj
d) V_awj = η*(1+ η)*V_wj
Answer: a
Clarification: 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*(1/(1+R))*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 (AWJ).
a) 2
b) 3
c) 5
d) 7
Answer: b
Clarification: 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
Clarification: 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
Clarification: 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.

250+ TOP MCQs on Laser Beam Machining – 3 and Answers

Manufacturing Processes Multiple Choice Questions on “Laser Beam Machining – 3”.

1. The flash tube is operated in _____ mode.
a) pulsed
b) continuous
c) reversed
d) synchronous
Answer: a
Clarification: 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
Clarification: Gas lasers can be:
• Axial flow
• Transverse flow
• Folded flow.

3. The power of CO₂ 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
Clarification: The power of a CO₂ 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 CO₂ lasers are made of folded design.

4. In a CO₂ laser, a mixture of _____ is circulated through the gas tube.
a) CO₂, N₂ and He
b) CO₂, N₂ and Ar
c) CO₂, H₂ and N₂
d) CO₂, I₂ and O₂
Answer: a
Clarification: In a CO₂ laser, a mixture of CO₂, N₂ and He continuously circulate through the gas tube. Such continuous recirculation of gas is done to minimize consumption of gases.

5. In CO₂ laser, ‘He’ gas is used for cooling purpose.
a) True
b) False
Answer: a
Clarification: CO₂ 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. CO₂ lasers are folded to achieve _____________
a) high power
b) high depth of cuts
c) high material removal rate
d) avoid over heating
Answer: a
Clarification: CO₂ 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
Clarification: 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 CO₂ laser is not used?
a) Plastics
b) Metals
c) Organic materials
d) Ceramics
Answer: b
Clarification: For,
• Plastics— CO₂ laser is used
• Metals—Nd-YAG, Ruby, Nd-glass lasers are used
• Organic materials and non-metals—Pulsed CO₂ laser is used
• Ceramics—Pulsed CO₂, 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
Clarification: 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 CO₂ 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
Clarification: 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.

250+ TOP MCQs on Annealing – 1 and Answers

Manufacturing Processes Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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) 10⁵ to 10⁶ m^-2
b) 10⁸ to 10¹⁰m^-2
c) 10¹⁰ to 10¹² m^-2
d) 10¹⁰ to 10¹⁵ m^-2
Answer: c
Clarification: 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 10¹⁰ to 10¹² m^-2, and heavily cold-worked metals can have approximately 10¹⁶.

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
Clarification: 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 10⁴to 10⁶.

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
Clarification: 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
Clarification: 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 retained strain 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
Clarification: 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
Clarification: 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
Clarification: 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.

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250+ TOP MCQs on CNC Machining and Answers

Manufacturing Processes Multiple Choice Questions 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
Clarification: 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 (known as chips), 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.