Advance Manufacturing Processes ( Manufacturing Engineering – II ) MCQs – Mechanical Engineering MCQs
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Mechanical Engineering MCQs – Advance Manufacturing Processes ( Manufacturing Engineering – II ) MCQs
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Electron Beam Machining – 1
1. Mechanism of material removal in Electron Beam Machining is due to _____
a) mechanical erosion due to impact of high of energy electrons
b) chemical etching by the high energy electron
c) sputtering due to high energy electrons
d) melting and vaporisation due to the thermal effect of impingement of high energy electron
Answer: d
Explanation: EBM is typically used with higher power density to machine materials. The mechanism of material removal is primarily by melting and rapid vaporisation due to intense heating by the electrons and laser beam respectively.
2. Electron beam machining is a/an _____ process
a) adiabatic
b) thermal
c) iso-thermal
d) isentropic
Answer: b
Explanation: Electron Beam Machining (EBM) is a thermal process considering the mechanisms of material removal. However electrical energy is used to generate high-energy electrons in case of Electron Beam Machining (EBM).
3. Electron beam machining is carried out in _____
a) high pressure vessel
b) thermally insulated area
c) vacuum
d) in a room at atmospheric pressure
Answer: c
Explanation: Electron Beam Machining is required to be carried out in vacuum. Otherwise, the electrons would interact with the air molecules, thus they would lose their energy and cutting ability.
4. During EBM _____ is kept under vacuum.
a) electron gun
b) whole setup
c) the workpiece
d) laser generation setup
Answer: c
Explanation: The workpiece to be machined is located under the electron beam and is kept under vacuum. The high-energy focused electron beam is made to impinge on the workpiece with a spot size of 10 – 100 μm.
5. As the electrons strike the work material _____
a) heat energy is converted to kinetic energy
b) atomic energy is converted to heat energy
c) kinetic energy is converted to heat energy
d) electrical energy is converted to heat energy
Answer: c
Explanation: The kinetic energy of the high velocity electrons is converted to heat energy as the electrons strike the work material. Due to high power density instant melting and vaporisation starts and “melt – vaporisation” front gradually progresses.
6. The gun in EBM is used in _____ mode.
a) wave guide
b) biasing
c) pulsed
d) high intensity
Answer: c
Explanation: Unlike in Electron Beam Welding, the gun in EBM is used in pulsed mode. Holes can be drilled in thin sheets using a single pulse. For thicker plates, multiple pulses would be required. Electron beam can also be manoeuvred using the electromagnetic deflection coils for drilling holes of any shape.
7. Which of the following is not a function of electron beam gun?
a) generation of electrons
b) accelerating the electrons
c) focusing the beam
d) absorbing the electron beam
Answer: d
Explanation: Electron beam gun is the heart of any electron beam machining facility. The basic functions of any electron beam gun are to generate free electrons at the cathode, accelerate them to a sufficiently high velocity and to focus them over a small spot size. Further, the beam needs to be manoeuvred if required by the gun.
8. ______ is used to make cathode for electron beam gun.
a) Aluminium
b) Rubidium
c) Molybdenum
d) Tantalum
Answer: d
Explanation: The cathode is generally made of tungsten or tantalum. Such cathode filaments are heated, often inductively, to a temperature of around 2500⁰C.
9. Heating to a high temperature leads to thermo-ionic emission.
a) True
b) False
Answer: a
Explanation: In EBM, temperature in the electron beam gun is around 2500⁰C. Such heating leads to thermo-ionic emission of electrons, which is further enhanced by maintaining a very low vacuum within the chamber of the electron beam gun.
10. In the electron beam gun, cathode cartridge is highly negatively biased.
a) True
b) False
Answer: a
Explanation: In the electron beam gun, cathode cartridge is highly negatively biased so that the thermo-ionic electrons are strongly repelled away from the cathode. This cathode is often in the form of a cartridge so that it can be changed very quickly to reduce downtime in case of failure.
Electron Beam Machining – 2
1. In electron beam machine, just after the cathode, there is/are _____
a) deflector coils
b) a magnetic lens
c) bias grid
d) port for vacuum gauge
Answer: c
Explanation: Just after the cathode, there is an annular bias grid. A high negative bias is applied to this grid so that the electrons generated by this cathode do not diverge and approach the next element, the annular anode, in the form of a beam.
2. Electron is accelerated by _____
a) cathode cartridge
b) electromagnetic coils
c) aperture
d) annular anode
Answer: d
Explanation: The annular anode now attracts the electron beam and gradually gets accelerated. As they leave the anode section, the electrons may achieve a velocity as high as half the velocity of light.
3. _____ determines the mode of an electron beam.
a) Applied voltage
b) Operating pressure
c) Position of magnetic lens
d) The nature of biasing
Answer: d
Explanation: The nature of biasing just after the cathode controls the flow of electrons and the biased grid is used as a switch to operate the electron beam gun in pulsed mode.
4. After the anode, the electron beam passes through _____
a) cathode cartridge
b) deflector coils
c) bias grid
d) a series of lenses
Answer: d
Explanation: After the anode, the electron beam passes through a series of magnetic lenses and apertures. The magnetic lenses shape the beam and try to reduce the divergence.
5. In the electron beam gun, apertures ______
a) allow only convergent electrons to pass
b) absorb convergent electrons
c) allow divergent electrons to pass
d) accelerate the electron beam
Answer: a
Explanation: The magnetic lenses shape the beam and try to reduce the divergence. Apertures on the other hand allow only the convergent electrons to pass and capture the divergent low energy electrons from the fringes. This way, the aperture and the magnetic lenses improve the quality of the electron beam.
6. In the final section of the electron beam gun, electron beam passes through the electromagnetic lens and deflection coil.
a) True
b) False
Answer: a
Explanation: After the apertures, the electron beam passes through the final section of the electromagnetic lens and deflection coil. The electromagnetic lens focuses the electron beam to the desired spot. The deflection coil can manoeuvre the electron beam, though by small amount, to improve the shape of the machined holes.
7. What is the purpose of a series of slotted rotating discs provided between the electron beam gun and the workpiece?
a) It increases the accuracy of the beam
b) It can increase the intensity of the beam (if needed)
c) It prevents power losses
d) It prevents vapour generated during machining to reach the gun
Answer: d
Explanation: Generally in between the electron beam gun and the workpiece, which is also under vacuum, there would be a series of slotted rotating discs. Such discs allow the electron beam to pass and machine materials but helpfully prevent metal fumes and vapour generated during machining to reach the gun. Thus it is essential to synchronize the motion of the rotating disc and pulsing of the electron beam gun.
8. For alignment of the beam, _____ is provided.
a) a lens
b) a telescope
c) magnifier
d) microscope
Answer: b
Explanation: Electron beam guns are also provided with illumination facility and a telescope for alignment of the beam with the workpiece. Lens are provided to focus the beam.
9. The workpiece is mounted on a CNC table.
a) True
b) False
Answer: a
Explanation: In electron beam machining, the workpiece is mounted on a CNC table so that holes of any shape can be machined using the CNC control and beam deflection in-built in the gun.
10. Level of vacuum within the gun is in the order of _____
a) 10-4 to 10-6 Torr
b) 10-1 to 10-3 Torr
c) 10-.0.65 to 10-1 Torr
d) 1 to 2 Torr
Answer: a
Explanation: One of the major requirements of EBM operation of electron beam gun is maintenance of desired vacuum. Level of vacuum within the gun is in the order of 10-4 to 10-6 Torr {1 Torr = 1mm of Hg}.
Electron Beam Machining – 3
1. In electron beam gun, vacuum is achieved by _____
a) reciprocating pump
b) rotary pump only
c) combination of rotary pump and diffusion pump
d) combination of diffusion pump and vane pump
Answer: c
Explanation: Maintenance of suitable vacuum is essential so that electrons do not lose their energy. Such a vacuum is achieved and maintained using a combination of rotary pump and diffusion pump. Diffusion pump is attached to the diffusion pump port of the electron beam gun.
2. Diffusion pump is an _____
a) oil filter equipment
b) oil heater
c) oil cooler
d) oil collector
Answer: b
Explanation: Diffusion pump is essentially an oil heater. As the oil is heated the oil vapour rushes upward where gradually converging structure is present.
3. The oil coming out of diffusion pump is evacuated by a _____
a) screw pump
b) gear pump
c) rotary pump
d) piston pump
Answer: d
Explanation: The nozzles change the direction of motion of the oil vapour and the oil vapour starts moving downward at a high velocity as jet. This oil is evacuated by a rotary pump via the backing line.
4. High velocity gets of oil vapour coming out of diffusion pump entrain ______ present within the gun.
a) water droplets
b) oil droplets
c) air molecules
d) hazardous gas molecules
Answer: b
Explanation: High velocity jets of oil vapour coming out of the diffusion pump entrain any air molecules present within the gun. The oil vapour condenses due to the presence of a cooling water jacket around the diffusion pump.
5. Which of the following parameters do not affect the electron beam machining process?
a) Accelerating voltage
b) Lens current
c) Spot size
d) Workpiece material
Answer: d
Explanation: The process parameters, which directly affect the machining characteristics in Electron Beam Machining, are:
• The accelerating voltage
• The beam current
• Pulse duration
• Energy per pulse
• Power per pulse
• Lens current
• Spot size
• Power density.
6. For the electron beam machining process, pulse duration for the electron beam is in range of_____
a) 10 μs to 90 μs
b) 50 μs to 15 ms
c) 80 μs to 10 ms
d) 15 ms to 1 s
Answer: b
Explanation: EBM the gun is operated in pulse mode. This is achieved by appropriately biasing the biased grid located just after the cathode. Switching pulses are given to the bias grid so as to achieve a pulse duration of as low as 50 μs to as long as 15 ms.
7. Beam current is in the range of _____
a) 50 μamp to 0.8 amp
b) 100 μamp to 10 amp
c) 200 μamp to 1 amp
d) 185 μamp to 1.5 amp
Answer: c
Explanation: Beam current is directly related to the number of electrons emitted by the cathode or available in the beam. Beam current once again can be as low as 200 μamp to 1 amp.
8. Increasing the beam current directly increases the _____
a) energy per pulse
b) accelerating voltage
c) spot size
d) lens current
Answer: a
Explanation: Increasing the beam current directly increases the energy per pulse. Similarly, increase in pulse duration also enhances energy per pulse. High-energy pulses (in excess of 100 J/pulse) can machine larger holes on thicker plates.
9. In electron beam machining process, the energy density is controlled by spot size.
a) True
b) False
Answer: a
Explanation: The energy density and power density is governed by energy per pulse duration and spot size. Energy density varies inversely with the spot size, i.e., higher energy density means lower spot size.
10. At higher energy densities, material removal rate is high.
a) True
b) False
Answer: a
Explanation: Spot size, on the other hand is controlled by the degree of focusing achieved by the electromagnetic lenses. A higher energy density, i.e., for lower spot size, the material removal would be faster through the size of the hole would be smaller.
Electron Beam Machining – 4
1. In electron beam machining, the plane of _____ is on the surface of the workpiece.
a) focusing
b) finishing
c) heating
d) drilling
Answer: a
Explanation: The plane of focusing would be on the surface of the workpiece or just below the surface of the workpiece. This controls the kerf shape or the shape of the hole.
2. _____ can manoeuvre the electron beam.
a) Nozzles
b) Magnetic lens
c) Electromagnetic coils
d) Deflector coils
Answer: d
Explanation: In electron beam gun assembly, the final deflection coil can manoeuvre the electron beam which helps in generating holes of non-circular cross-section as required.
3. Electron beam machining process can machine holes of diameters in the range of _____
a) 10 μm to 80 μm
b) 50 μm to 100 μm
c) 100 μm to 2 mm
d) 2 mm to 5 mm
Answer: c
Explanation: Electron beam machining can provide holes of diameter in the range of 100 μm to 2 mm with a depth up to 15 mm, i.e., with a length/diameter ratio of around 10.
4. Which of the following is true about electron beam machining (EBM)?
a) By EBM process, tapered holes can be generated
b) Electro-magnetic coils are used to change the direction of the electron beam
c) Electron beam gun works under high pressure
d) Increasing the current density increases the spot size
Answer: a
Explanation: Electron beam machining can generate a hole which can be tapered along the depth or barrel shaped. By focusing the beam below the surface a reverse taper can also be obtained.
5. Which of the following holds true for electron beam machining?
a) This process does not generate burr
b) Holes having length/diameter ratio as high as 50 can be machined by this process
c) In electron beam gun, magnetic lens is used to diverge the beam
d) Electron beam is accelerated by electromagnetic coils
Answer: a
Explanation: Generally burr formation does not occur in electron beam machining. There would be an edge rounding at the entry point along with a presence of recast layer. Also, magnetic lens is used to focus the beam at a single point. Annular anodes are used to accelerate the beam.
6. Which of the following materials is not machined by the EBM process?
a) Titanium
b) Wood
c) Plastic
d) Leather
Answer: b
Explanation: Materials which can be machined by EBM are:
• Commercial grade steel
• Stainless steel
• Ti and Ni super alloys
• Aluminium plastics
• Ceramics
• Leathers.
7. For EBM process, heat affected zone is about _____
a) 10 μm to 80 μm
b) 20 μm to 30 μm
c) 100 μm to 1 mm
d) 2 mm to 5 mm
Answer: b
Explanation: In electron beam machining, the heat-affected zone is rather narrow due to the shorter pulse duration. Typically, the heat affected zone is around 20 μm to 30 μm.
8. Which of the following materials are easy to a machine by EBM process?
a) Aluminium
b) Steel
c) Plastic
d) Wood
Answer: a
Explanation: EBM can machine steel titanium alloys, aluminium, plastics, nickel alloys, etc., but some of the materials like Al and Ti alloys are more readily machined compared to steel.
9. Number of holes drilled per second depends on the holes diameter.
a) True
b) False
Answer: a
Explanation: Number of holes drilled per second depends on:
• hole diameter
• power density
• depth of the hole
• material type.
10. While machining, there are chances of thermal damage associated with EBM.
a) True
b) False
Answer: a
Explanation: As the mechanism of material removal is thermal in nature as for example in electro-discharge machining, there would be thermal damages associated with EBM. On the contrary, heat affected zone is narrow.
Laser Beam Machining – 1
1. Mechanism of material removal in Laser Beam Machining is due to _____
a) mechanical erosion due to impact of high of energy photons
b) electro-chemical etching
c) melting and vaporisation due to thermal effect of impingement of high energy laser beam
d) fatigue failure
Answer: c
Explanation: Laser beam machining is carried out utilizing the energy of coherent photons or laser beam, which is mostly converted into thermal energy upon interaction with most of the materials.
2. Laser Beam is produced due to _____
a) spontaneous emission
b) stimulated emission followed by spontaneous emission
c) spontaneous emission followed by Spontaneous absorption
d) spontaneous absorption leading to “population inversion” and followed by stimulated emission
Answer: d
Explanation: Lasing process describes the basic operation of laser, i.e. generation of a coherent (both temporal and spatial) beam of light by “light amplification” using “stimulated emission”.
3. Which of the following processes does not use lasers?
a) Cladding
b) Alloying
c) Nitriding
d) Cutting
Answer: c
Explanation: Laser Beam Machining or more broadly laser material processing deals with machining and material processing like heat treatment, alloying, cladding, sheet metal bending, etc.
4. Lasers are also used for_____
a) riveting
b) nitriding
c) rapid prototyping
d) facing
Answer: c
Explanation: Nowadays, laser is also finding application in regenerative machining or rapid prototyping as in processes like stereo-lithography, selective laser sintering etc.
5. Laser stands for light amplification by stimulated emission of radiation.
a) True
b) False
Answer: a
Explanation: Laser stands for light amplification by stimulated emission of radiation. The underline working principle of a laser was first put forward by Albert Einstein in 1917 through the first industrial laser for experimentation was developed around the 1960s.
6 Laser beams can have power density upto _____
a) 1 kW/mm2
b) 10 kW/mm2
c) 1 MW/mm2
d) 10 MW/mm2
Answer: c
Explanation: Laser beam can very easily be focused using optical lenses as their wavelength ranges from half micron to around 70 microns. Focussed laser beam as indicated earlier can have power density in excess of 1 MW/mm2.
7. Laser causes a rapid substantial rise in _____ of the material.
a) local temperature
b) local pressure
c) indentation
d) cracks
Answer: a
Explanation: As laser interacts with the material, the energy of the photon is absorbed by the work material leading to rapid substantial rise in local temperature. This in turn results in melting and vaporisation of the work material and finally material removal.
8. At _____ temperature an atom is considered to be at ground level.
a) absolute zero
b) 0oC
c) 100oC
d) 100 K
Answer: a
Explanation: Each of the orbital electrons is associated with unique energy levels. At absolute zero temperature an atom is considered to be at ground level when all the electrons occupy their respective lowest potential energy.
9. The electrons at ground state can be excited to a higher state of energy by _____
a) increasing the pressure
b) lowering the energy
c) absorbing the energy
d) oxidising the atom
Answer: c
Explanation: The electrons at ground state can be excited to higher state of energy by absorbing energy form external sources like increase in electronic vibration at elevated temperature, through chemical reaction as well as via absorbing the energy of the photon.
10. The geometry and radii of orbital paths of electrons depend on the presence of an electromagnetic field.
a) True
b) False
Answer: a
Explanation: In the model of an atom, negatively charged electrons rotate around the positively charged nucleus in some specified orbital paths. The geometry and radii of such orbital paths depend on a variety of parameters like number of electrons, presence of neighbouring atoms and their electron structure, presence of an electromagnetic field, etc.
Laser Beam Machining – 2
1. When coming back to normal state from excited state, electron releases _____
a) proton
b) anti-proton
c) positron
d) photon
Answer: d
Explanation: On reaching the higher energy level, the electron reaches an unstable energy band. And it comes back to its ground state within a very small time by releasing a photon. This is called spontaneous emission.
2. In population inversion, no of electrons in _____ are more as compared to numbers of electrons in _____
a) quasi-stable state, ground state
b) meta-stable state, ground state
c) meta-stable state, quasi-stable state
d) mono-stable state, ground state
Answer: b
Explanation: Sometimes such change of energy state puts the electrons in a meta-stable energy band. Instead of coming back to its ground state immediately (within tens of ns) it stays at the elevated energy state for micro to milliseconds. In a material, if more number of electrons can be somehow pumped to the higher meta-stable energy state as compared to the number of atoms at ground state, then it is called “population inversion”.
3. In laser beam machine, one end of the glass is_____
a) open
b) blocked with a 10% reflective mirror
c) blocked with a 75% reflective mirror
d) blocked with a 100% reflective mirror
Answer: d
Explanation: The gas, called lasing medium is enclosed in a cylindrical glass vessel. One end of the glass is blocked with a 100% reflective mirror and the other end is having a partially reflective mirror.
4. In laser beam machining, electrons are excited by _____
a) high temperature steam
b) flash lamps
c) flash torch
d) cathode ray tube
Answer: b
Explanation: Population inversion can be carried out by exciting the gas atoms or molecules by pumping it with flash lamps. Then stimulated emission would initiate lasing action. Stimulated emission of photons could be in all directions.
5. The photons emitted in the _____ direction form a laser beam.
a) vertical
b) horizontal
c) longitudinal
d) lateral
Answer: c
Explanation: Most of the stimulated photons, not along the longitudinal direction would be lost and generate waste heat. The photons in the longitudinal direction would form coherent, highly directional, intense laser beam.
6. How many types of lasers are there?
a) 2
b) 3
c) 4
d) 5
Answer: a
Explanation: Many materials can be used as the heart of the laser. Depending on the lasing medium lasers are classified as:
• Solid-state laser
• Gas laser.
7. How many types of solid state lasers are there?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: Solid-state lasers are commonly of the following type:
• Ruby which is a chromium – alumina alloy having a wavelength of 0.7 μm
• Nd-glass lasers having a wavelength of 1.64 μm
• Nd-YAG laser having a wavelength of 1.06 μm
These solid-state lasers are generally used in material processing.
8. Lasers can be operated in _____ modes
a) 2
b) 7
c) 8
d) only one
Answer: a
Explanation: Lasers can be operated in
• continuous mode, or
• pulsed mode
Typically CO2 gas laser is operated in continuous mode and Nd – YAG laser is operated in pulsed mode.
9. Helium-Neon is a gas laser.
a) True
b) False
Answer: a
Explanation: The generally used gas lasers are:
• Helium – Neon
• Argon
• CO2 etc.
10. Flash tubes used for Nd-YAG laser can be helical or flat.
a) True
b) False
Answer: a
Explanation: Nd-YAG laser is pumped using a flash tube. Flash tubes can be helical, or they can be flat. Typically the lasing material is at the focal plane of the flash tube. Though helical flash tubes provide better pumping, they are difficult to maintain.
Laser Beam Machining – 3
1. The flash tube is operated in _____ mode.
a) pulsed
b) continuous
c) reversed
d) synchronous
Answer: a
Explanation: The flash tube is operated in pulsed mode by charging and discharging of the capacitor. Thus the pulse on time is decided by the resistance on the flash tube side and pulse off time is decided by the charging resistance. There is also a high voltage switching supply for initiation of pulses.
2. How many types of flows are possible in gas lasers?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: Gas lasers can be:
• Axial flow
• Transverse flow
• Folded flow.
3. The power of 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: For drilling holes as small as 0.25mm and as large as 1.5mm diameter, following lasers are used;
• Nd-YAG,
• Nd-glass, and
• Ruby.
8. For which of the following materials CO2 laser is not used?
a) Plastics
b) Metals
c) Organic materials
d) Ceramics
Answer: b
Explanation: 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
Explanation: Following are the limitations of laser beam machining;
• High initial capital cost
• High maintenance cost
• Not very efficient process
• Presence of Heat Affected Zone – specially in gas assist 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
Explanation: Following are the advantages of laser beam machining:
• In laser machining, there is no physical tool. Thus no machining force or wear of the tool takes place.
• Large aspect ratio in laser drilling can be achieved along with acceptable accuracy or dimension, form or location
• Micro-holes can be drilled in difficult – to – machine materials
• Though laser processing is a thermal processing but heat affected zone especially in pulse laser processing is not very significant due to the shorter pulse duration.