Special or Unique welding
processes
Plasma Arc Welding
Solid State Welding
Radiant Energy Welding Process
• Radiant Energy Beam focuses an energy beam
on the work-piece. The heat is generated only
when the energy beam strikes the work-piece.
Radiant Energy beam includes
1. Laser Beam Welding
2. Electron Beam Welding
Laser Beam Welding
• Laser Beam Welding is defined as a welding process wherein coalescence
is produced by the heat obtained from the application of a concentrated
coherent (waves are identical and parallel) light beam impinging upon the
surfaces to be joined.
• LASER :- Light Amplification by the Stimulated Emission of Radiation.
• In Laser Beam welding radiation from an intense source of light is
concentrated and amplified using a laser crystal.
• The laser beam is focused on the work-piece and heat generated is used
to weld the joint.
• This process is used for cutting and welding of metals.
• High melting point metals (stainless steel, tungsten, titanium etc) can be
welded by this process.
• Vacuum is not necessary for laser beam welding.
• Good welding speed can be obtained.
Welding Equipment
• Laser Welding System consists of
1. A cylindrical Ruby Crystal. Ruby is aluminum oxide
with chromium dispersed through it.
2. Flash tube containing inert gas – xenon is placed
around the crystal. Flash Tube converts electrical
energy into light energy.
3. Capacitor bank stores electrical energy. It is charged
with high voltage power supply. Flash tube is energized
by electrical discharge from the capacitor.
4. Optical focusing lens for focusing the laser beam to
produce small intense spot on the job.
Electron Beam Welding
• Electron Beam make use of the kinetic energy of
the fast moving electrons for welding operation.
• When fast moving electrons strike the parts to be
welded, they give up kinetic energy into heat.
• Welding is carried out under High vacuum.
• The heat generated is about 2500°C.
• Electron beam emitting from the tungsten
electrode is accelerated is focused on to the parts
to be welded.
Steps :
1. Joint Preparation : Joint gas about 0.05 to .075mm
maximum used for making narrow welds.
2. Before welding work-piece is cleaned.
3. Residual magnetism if present can cause deflection of
electron beam. It is relieved by placing the work-piece in a
fifty cycle inductive field.
4. The work-piece is then placed in the welding chamber.
5. The chamber is pumped down to the required vacuum.
6. The work-piece is preheated if necessary.
7. Welding is initiated.
Welding operation can be carried out in
1. High Vacuum : In this type both the electron gun and
the work-piece are enclosed in the same vacuum
chamber. Vacuum assures decontamination and
degasification of the molten metal being formed during
the process. Also in vacuum assures little loss of beam
energy. How ever size of the vacuum chamber limits the
size of the work-piece to be welded.
2. Partial Vacuum : In this type both the electron gun and
the work-piece are enclosed in the separate vacuum
chamber. An orifice permits the electron to pass from gun
chamber to work-piece chamber.
3. Atmosphere : In this case, work-piece is placed out side
the vacuum chamber.
Thermo-chemical Welding Process
• Thermo-chemical welding process make uses
of heat energy liberated by chemical reactions
(Exothermic Reactions) to carry out welding.
Various Thermo-Chemical reactions are
1. Thermit Welding
2. Atomic Hydrogen Welding
Thermit Welding
• Thermit Welding is a Fusion process.
• Thermit process is based on a chemical reaction which generates
heat (Exothermic reaction).
• Thermit is a mixture of aluminum and iron oxide.
• Weld is formed by pouring superheated thermit around the parts to
be united.
• Temperature produced by the Thermit reaction is around 3000°C.
• A few Thermit reactions are
1.
2.
3.
4.
8Al + 3 Fe3O4 = 4Al2O3 + 9Fe (3088°C)
2Al + Fe3O4 = Al2O3 + 2Fe (2960°C)
3 CuO + 2Al = Al2O3 + 3Cu (4865°C)
Cr2O3 +2Al = 2Cr + 2Cr (2977°C)
Steps :
• Joint is cleaned.
• Parts to be welded are lined up with a space about 1.5mm to 6mm
between the ends.
• A pattern of wax is shaped around the parts to be welded.
• An iron box is placed around the pattern and space between the
pattern and box is filled and rammed with sand. Runners and gates
are cut in the sand.
• Before pouring thermit, the parts to be welded are preheated to
prevent the chilling of steel.
• During preheating the wax pattern melts off.
• Then the superheated metal from produced by the thermit reaction
is poured in the mold surrounding the parts to be welded.
• Mechanical pressure is applied to complete the weld.