What is Electron beam machining or EBM ?
Electron beam machining (EBM) is a non conventional machining process which uses the high velocity focused electrons beam for the machining.
These electrons have high velocity about 200,000 km/s, that is at 65% of speed of the light.
EBM is used for the machining of the brittle & hard materials which are cannot be machined by conventional machining. It is suitable for the machining of the small parts.
The Electron Beam machining works on the following principle:-
When the high velocity electrons fall on the work-piece surface, the kinetic energy of these electrons gets converted into the heat energy that vaporizes the metal from the work-piece surface.
In such a way, material removal takes place in EBM.
EDM is carried out inside the vacuum chamber because if electrons comes in contact with particles in atmospheric air, then electrons will lose their energy.
This machining process is consists of the following components:
1) Power supply:
Power supply provides the high voltage in range of 50 kV-200 kV to the electron gun for the acceleration of the electrons to the 200,000 km/s.
The positive terminal of the power supply is connected to the anode and the negative terminal is connected to the cathode.
2) Electron gun:
It is source of the electron beam which is consists of the tungsten filament, cathode, control grid, anode.
A) Tungsten filament:- The tungsten filament is made of the tungsten material which coverts the electrical energy into heat energy. When power starts to flow across the electron gun, this tungsten filament generates heat, due to which the heated cathode generates an electron beam.
B) Cathode:- Cathode is the source of electrons. The negative terminal of the power source is connected to the cathode. When the filament gets on, the cathode emits the electron beam.
C) Control grid:- Control grid is the nickel cylinder having 15 mm length & diameter of 15 mm, which is located after the cathode.
It has drilled hole of 0.25 mm for the flow of electron beam through it. The control grid is negatively biased, hence it controls the flow of electron beam.
D) Anode:- The anode is connected to the positive terminal of the power source. Anode accelerates the electron beam passing through the electron gun at about 2000,000 km/s which is 65% of the speed of the light.
3) Tungsten Diaphragm:
The tungsten diaphragm removes the stray electrons from the electron beam.
4) Focusing lens:
It is an electromagnetic lens which shapes the divergence of electron beam and focus it on the work-piece surface.
The focusing lens is made up of copper wire coils into the iron pole pieces.
5) Deflector coil:
It is the magnetic coil located below the focusing lens which bends the electron beam to directly falls it on the desired point of work-piece surface.
6) Work-piece Table:
Work-piece table firmly holds the work-piece on it. It can move in x, y & z axes as per requirement.
This advanced machining process works in the following manner:
a] Electron emission:
When high voltage power supply (In range of 50 kV-200 kV) starts flow towards electron gun, tungsten filament converts this electrical energy into the heat energy. The tungsten filament becomes hot around, 2000°C.
This heated tungsten filament heats the cathode. Due to heat, the cathode starts emitting electrons.
b] Controlling and accelerating electrons:
After the cathode, this electron beam goes through the control grid. It controls the flow of electron beam.
The electron beam from the control grid is then passed to the anode. The anode accelerates this electron beam at about 200,000 km/s which is 65% of the speed of the light.
c] Removing stray electrons:
The high velocity electron beam then passed through the tungsten diaphragm, that removes the stray electrons from the high velocity electron beam.
d] Focusing and bending the beam:
After the tungsten diaphragm, the electron beam passes through a focusing lens. The focusing lens reduces the diverging of the high velocity electron beam and focuses it on the work-piece surface.
The focused electron beam from the focusing lens goes through a deflector coil, which bends the beam to fall directly to the required point on the work-piece surface.
This high velocity electron beam impinges onto the work-piece surface, where its kinetic energy converts into heat energy. This heat melts and vaporizes the material from the work-piece surface.
Therefore, in such way machining is carried out in electron Beam Machining with the help of high velocity electron beam.
The characteristics of the EBM are as follows:-
- Power supply in range of 50 kV-200 kV.
- Capacity of 4000 holes per second.
- Velocity of electron beam, about 200,000 km/sec.
- Beam current in range of 200 micro-ampere to 1 Ampere.
- Pulse generation by control grid which is negatively biased with pulse duration around 50 microseconds to 15 milliseconds.
- It can produce small diameters hole of 0.1 mm to 1.4 mm.
The EBM has the following advantages:-
- Less tool wear since no physical contact between tool & work-piece
- Better surface finish
- High drilling rate which is up to 4000 hole per second
- Very closed dimensional tolerances can be achieved.
- High dimensional accuracy obtained.
- Hard and brittle material can be machined.
- It is best suited for the machining of small parts.
- Possible of machining of electrical conducting materials.
- Less heat affected zone.
- It can drill different shape & size holes.
- Less operating cost.
The EBM has the following disadvantages:-
- It has less material removal rate.
- When an electron beam falls on a work-piece, it produces hazardous x-rays. Hence, high skilled operator required.
- It has limited machining thickness of 10 mm.
- Costly equipment’s required.
- EBM is required to be carried out in vacuum chamber.
- Power consumption is high.
Electron beam machining applications:
It has the following applications:-
- In drilling multiple hole at one time.
- In automobile industries for machining smaller parts.
- For the drilling of non-circular holes on workpiece.
- In drilling small size holes in aerospace industry.
What is the mechanism of material removal in electron beam machining?
In EBM, when the high velocity electrons hit the workpiece surface, the kinetic energy of the electron gets converted into the heat energy that vaporizes the metal from the workpiece.
Why EBM is carried out in vacuum?
If electrons come in contact with particles in atmospheric air, then electrons will lose their energy. Hence, the EBM process is carried in vacuum.
What does EBM stand for?
EBM stands for Electron Beam Machining.