ELECTRON BEAM WELDING
Principle
Beam of electron is used for producing high temperatures and melting the work piece to be welded.
Working
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
1. Voltage
2. Speed
3. Distance between beam gun to work piece
FRICTION WELDING
Principle
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.
Working
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
2. Speed
3. Burn off
The materials that can be welded are listed below
1. Brass of Bronze
2. Nickel
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
DIFFUSION WELDING
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.
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