Engineering Questions with Answers - Multiple Choice Questions
Manufacturing Processes – Electron Beam Machining – 3
1 - Question
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
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 - Question
Diffusion pump is an _____
a) oil filter equipment
b) oil heater
c) oil cooler
d) oil collector
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 - Question
The oil coming out of diffusion pump is evacuated by a _____
a) screw pump
b) gear pump
c) rotary pump
d) piston pump
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 - Question
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
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 - Question
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
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 - Question
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
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 - Question
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
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 - Question
Increasing the beam current directly increases the _____
a) energy per pulse
b) accelerating voltage
c) spot size
d) lens current
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 - Question
In electron beam machining process, the energy density is controlled by spot size.
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 - Question
At higher energy densities, material removal rate is high.
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.