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}.