Engineering Questions with Answers - Multiple Choice Questions
Manufacturing Processes – Electron Beam Machining – 2
1 - Question
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
View Answer
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 - Question
Electron is accelerated by _____
a) cathode cartridge
b) electromagnetic coils
c) aperture
d) annular anode
View Answer
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 - Question
_____ determines the mode of an electron beam.
a) Applied voltage
b) Operating pressure
c) Position of magnetic lens
d) The nature of biasing
View Answer
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 - Question
After the anode, the electron beam passes through _____
a) cathode cartridge
b) deflector coils
c) bias grid
d) a series of lenses
View Answer
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 - Question
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
View Answer
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 - Question
In the final section of the electron beam gun, electron beam passes through the electromagnetic lens and deflection coil.
a) True
b) False
View Answer
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 - Question
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
View Answer
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 - Question
For alignment of the beam, _____ is provided.
a) a lens
b) a telescope
c) magnifier
d) microscope
View Answer
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 - Question
The workpiece is mounted on a CNC table.
a) True
b) False
View Answer
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 - Question
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
View Answer
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}.