Electron Beam Welding Process is a fusion welding process in which a high velocity electron beam is used to join two metals together. The high velocity electron beam when strikes the weld area of two metal pieces and very intense heat is generated which melts the metal and they fuse together to form a strong weld. The whole process is carried out in vacuum chamber to prevent it from contamination.
It was developed by the German physicist Karl-Heinz Steigerwald. In 1958 he introduced the first practical EBW machine that was put into operation
It works on the principle that when a high velocity beam of electron that has Kinetic energy strikes the two metal pieces, the kinetic energy of the electron transformed into heat. The intensity of heat produced is so much that it melts the two metal pieces and fuse them together to form a strong weld.
The various Equipment of Electron beam welding are
1. Electron Gun
It is used to generate, accelerates and align the electron beam in a desired direction and spots on the w/p. There are two types of electron gun, first one is self accelerated and second one is work accelerated. In self accelerated gun, the acceleration of electron takes by applying potential difference between cathode and anode. And in work accelerated gun, the acceleration of the electron takes place by applying the potential difference between the cathode and workpiece. The workpiece (w/p) acts as anode.
The main parts of electron gun are:
(i) Cathode (Emitter or Filament): It emits the electron.
(ii) Anode: It is a positively charged Electrode and attracts the electron produced by the cathode. It accelerated the electrons under the influence of high potential difference. For high voltage equipments, the potential difference ranges from 70 kV to 150 kV and for small voltage equipment it ranges from 15 – 30 kV
(iii) Grid Cup: It is used to control the electron beam. It stops the divergence of electrons produced by the cathode. It has applied with negative voltage with respect to the cathode.
(iv) Focusing Unit: Tt consists of two parts – magnetic lens and deflector coil. The magnetic lens focuses the electron beam on the w/p. And the deflector coil is used to deflect or guide the beam to the desired locations. The extent of deflection can be varied by changing the amount of dc voltage across the deflector plate.
2. Power Supply
The power supply used in Electron Beam Welding process is dc power supply sources. The voltage ranges from 70-150 kV for high voltage equipments and 5-30 kV for small voltage equipment. The current level ranges from 50 to100 mA.
3. Vacuum Chamber
It is a chamber in which the vacuum is created by the vacuum pump. Roughing mechanical pump and diffusion pump is used to create the vacuum in the vacuum Chamber.The pressure ranges from 100 kPa for open atmosphere to 0.13-13 Pa for partial vacuum and 0.13 to 133 mPa for hard vacuum. The extent of scattering increases with the increase in the vacuum and this allows more penetration in the workpiece.
4. Work Handling Devices:
The fixtures are used to hold the workpiece. The workpiece motion is controlled by the CNC (Computer Numerical Control).
Working of Electron Beam Welding Process
- In Electron Beam welding , the electron is produced by the cathode of the electron gun.
After cathode a cup grid is provided. It prevents the divergence of electron and control it.
- Because of the high voltage applied across the cathode and anode. The anode which is positively charged attracts the electron from the cup grid.
- The anode accelerates the electron and its velocity increase and reaches to the range of 50000 – 200000 km/s. From the anode the high velocity electron beam is passed through the magnetic lens and deflector coils.
- The magnetic lens focuses the electron beam to the desired location on the workpiece. And the deflector coil deflect the beam to the required weld area. As the high velocity electron beam strikes the workpiece, an intense heat is produced and it melts the metal of the two workpiece and fill the weld area. The molten weld solidifies and forms a strong weld joint.
- High welding speed.
- Welding of dissimilar metal can be done.
- High weld quality and precision.
- Less operating cost.
- Materials with high welding temperature can be welded easily.
- Less distortion due to less affected heat zone.
- Cost of cleaning is negligible.
- It welds thicker sheets, ranges from .025 mm to 100 mm.
- It is capable of welding inaccessible joints.
- Cost of equipment is very high.
- High skilled operator is required to operate it.
- High vacuum is required.
- Due to operation in vacuum, large jobs can not welded.
- High safety measures are need to work with it.
- It is used in aerospace industries for manufacturing jet components, parts of structures, transmission parts and sensors.
- It is used in power generation industries.
- It is used in space industries to build titanium tanks and sensors.
- It is used in automobile industries to manufactures transmission system, gears and turbochargers.
- It used in electrical and electronical industries to manufactures parts of copper structures.
- The other areas where it is used are nuclear industries, medical, research centres etc .