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.