Welding Using an Electron Beam (EBW)
When the electron beam impinges on the work piece in the EBW process, heat is created.
When the high-velocity electron beam collides with the to-be-welded surfaces, its kinetic energy is converted to thermal energy, causing the workpiece metal to melt and fuse.
The heat generated by the impact of a narrow focused beam of high velocity electrons on the object to be welded is employed in electron beam welding (EBW).
Electrons’ kinetic energy is turned into heat, which melts the surface and creates a hole.
As the weld advances, the molten metal from this hole flows back into the joint region, resulting in a deep, narrow weld with little or no deformation.
A high-voltage (50 to 100 kV) current is used to heat a tungsten filament to roughly 2200°C, causing it to release electrons.
An electron cannon is used in this technique, with the cathode being a hot tungsten or tantalum filament that generates a stream of electrons.
Because of the significant potential difference between the filament and the anode, the electrons released via thermionic emission are accelerated to a high velocity.
These electrons are accelerated to an extremely high speed using a control grid, an accelerating anode, and focusing coils, forming a narrow beam that can be focused onto the workpiece in a circular spot about 1 mm in diameter.
A magnetic lens device focuses the electron beam on the workpieces to be welded.
The speed of electrons in a normal environment is slowed to the point that the process is rendered inefficient.
As a result, the electron beam must be created and focussed in an extremely high vacuum (say, at a pressure of 0.01 Pa) to be effective as a heat source for welding.
Even the workpiece to be welded is usually enclosed in the high vacuum chamber in most applications.
The electron speed, which is influenced by the accelerating voltage, determines the depth of penetration of the weld.
The current values are low, ranging from 50 to 1000 milliamperes.
Because the heat released is low and concentrated in a small area, the heat affected zone is small, and weld deformities are nearly minimised.
It is feasible to do electron beam welding in an open environment.
The workpiece is contained in a box in which the vacuum is created when welding in vacuum.
When an electron beam goes through a normal atmosphere, the electrons collide with the gas molecules in the atmosphere, scattering them.
As a result of the scattering, the electron beam’s spot size grows larger, and penetration decreases.
The scattering effect of the electron beam diminishes as the vacuum increases, and hence penetration rises. Another benefit of vacuum welding is that the weld metal is not polluted.
Pros:
- Because vacuum ensures both de-gasification and de-contamination, welds are of great purity and quality.
- Welds have a thin profile and penetrate deeply. The depth-to-width ratio of a fusion zone can be as high as 25:1.
- The heat impacted zone is usually only 2-5 percent of what is produced in arc welding procedures.
- The amount of distortion in the weld area is minimal.
- Butt or lap welding can be used on almost any metal with a thickness of 0.2 mm to 100 mm.
- Metals like zirconium, beryllium, and tungsten, which are difficult to weld using traditional procedures, can be welded.
- Welding can also be done with metals that aren’t the same.
- Heat-sensitive materials can be welded without any damage to the workpiece material
- The procedure can be carried out from any position.
- Welding speed is high. Welding speeds of up to 10 mpm are possible when parameters are accurately controlled with servo controls.
- There is no need for shielding gas, flux, or filler metal.
- Because the weld is not polluted, no pre-welding or post-welding processes are required.
Cons:
- The equipment used in the procedure is costly.
- Because the technology releases hazardous X-rays, significant safety precautions in terms of pricey shielding are required.
- Extensive joint preparation and alignment are required.
- The size of the workpiece that can be accommodated in the vacuum chamber is limited.
- The process productivity is low because it takes a long time to re-establish the vacuum each time a new task is fed into the chamber.
- Not recommended for applications requiring a large gap filling.
Applications:
- In this case, thin and thick parts must be welded together.
- When alternative welding procedures fail to deliver the desired outcomes. That is, where the required weld quality is relatively high.
- When a lot of penetrating power is required.
- In the automobile and electronics sectors, for example.
- In the aerospace and aircraft sectors.
- Welding of reactive materials (nuclear reactor) and missile components in the military industry.
