ELECTRON BEAM WELDING
Beam of electron is used for producing high temperatures and melting the work piece to be welded.
When tungsten filament is electrically heated in vacuum, it will emit the electrons. These electrons carry a negative charge which is passed through the anode hole. The electron beam is focused by the focusing lens. When the focused electron beam strikes the work piece, the kinetic energy of this electron beam is converted into heat energy.
This heat energy is used to weld the metals. The operation is carried out in vacuum. So, it is possible to weld holes. The beams are focused about 0.25 to 1mm diameter and power density of 10kW/mm aluminium material having focusing length of about 40mm and steel about 30mm.
The variables which are controlled in the electron beam welding are
3. Distance between beam gun to work piece
It is a solid state welding process wherein coalescence is formed by the heat which is obtained from mechanically induced sliding motion between rubbing surfaces.
Initially, the components to be welded are held under pressure. One part is rotated at high speed and other part is held stationary. In this welding, the movable clamp is moved and contacted with the rotating component. The heat is produced between contact surfaces. This heat is used to weld the components under pressure. The pressure during welding may be about to few Mpa.
During this period, metal is slowly extruded from the weld region to form on upset For stopping the relative motion, the brake system is applied.
Parameters which are considered in friction welds are
1. Friction Pressure
3. Burn off
The materials that can be welded are listed below
1. Brass of Bronze
3. Titanium alloys
4. Stainless steel
5. Aluminium & Aluminium alloys
The basic joints are made by friction welding as follows
1. Bar-belt joint
2. Bar-ball joint
3. Tee-butt joint
It is a solid state joining process in which the strength of the joint results primarily from diffusion. This process requires temperature of about 0.5 in order to have a high diffusion rate between the parts being joined. The strength of the welding depends on pressure, temperature, time of contact and the Cleanliness of the metal. The example for diffusion welding is bonding of gold over copper. First, a thin layer of gold foil is obtained by hammering. The gold is then located over copper and then weight is placed on top of it. The assembly is then placed in a furnace and left until a good bond is obtained.
Generally in diffusion welding, pressure may be applied by dead weight or a by a press using differential gas pressure. The parts are usually heated in a furnace or by electrical resistance. The diffusion welding is suitable for dissimilar metals. It is also used in reactive metals like titanium, zirconium and refractory metal alloys. The diffusion welding process is very slow when compare to other welding process.