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Specialty Welding Processes

Explosion

Explosive Welding

Explosive welding is a solid state welding process, that uses a controlled explosive detonation to usually fuse two dissimilar metals together at high pressure. The result is a composite durable, metallurgical bond.

Explosive welding under high velocity impact was first recognized in 1944. In 1957 in the United States it was observed that metal sheets being explosively formed occasionally stuck to the metal dies, and now the process has been developed fully with large applications in the manufacturing industry.

An explosive detonated on the surface of a metal, generates a high pressure pulse and propels the metal at a very high rate of speed. When the piece of metal collides at an angle with another piece of metal, welding occurs. A jetting action is required at the collision interface of the two pieces of metals colliding. This reaction cleans the metals and allows two pure metallic surfaces to join under extremely high pressure. The metals do not mix, they are atomically fused. Due to this fact, different metal types may be welded, (i.e., copper  to steel, titanium to stainless, etc.). Typical impact pressures are in the millions of pounds per square inch.

Explosive welding is used to weld tubing, and pipe typically in exchanger, and pressure vessel tube sheets,  for plugging pipe and tubing, attaching cooling fins to rotors, and is used in joining dissimilar metals that are not weldable by standard welding processes.

Plasma Arc Welding

The plasma arc welding process was introduced to the welding industry in 1964, bringing better control to the arc welding process in lower current settings. Today, plasma arc welding retains its original advantages brought to the welding industry by advanced level of control and accuracy to produce high quality welds in miniature or precision applications, and providing long electrode life for high production applications. Plasma arc welding is suited to both manual, and automatic procedures. It has been used for high volume welding of strip metal, precision welding of surgical instruments, automatic repair of jet engine blades, and manual welding of kitchen equipment for the food and dairy industry.

Plasma is a gas which is heated to an extremely high temperature and ionized so that it becomes electrically conductive. Similar to the GTAW (Tig) welding process, the plasma arc welding process uses plasma to transfer the electric arc to a work piece. The metal to be welded is melted by the intense heat of the arc and fuses together. A tungsten electrode is located within the plasma welding torch, which is surrounded by a copper nozzle having a small opening at the tip. A pilot arc is initiated between the torch electrode and nozzle tip. This arc is then transferred to the metal to be welded forcing the plasma gas and arc through a constricted orifice, the torch delivers a high concentration of heat to a very small area, producing extremely high quality welds. The plasma gas is normally argon. The torch also uses a shielding gas, argon, argon/hydrogen or helium which assists in protecting the molten weld puddle, and minimizing oxidation of the weld.

Laser Beam Welding

Modern Laser Beam Welding (LBW) is a high energy beam process that is expanding into modern industries and new applications because of many advantages including, deep weld penetration and minimal heat inputs. Automating laser welding processes, has led to expansion, and using high technology like the use of laser and computers to improve product quality through more accurate control of laser welding processes. The laser welding process works by converting a large concentration of light energy to thermal energy on the surface of the material, or parts to be welded. Weld penetration is determined by the conduction of the generated heat, and limits material thickness to generally less than 0.80 inches.

The heat source in the laser welding process is the energy of light, thus the workpiece will be welded purely, meaning the fatigue strength of the welded joint will be excellent. Laser welding is used in the aerospace, defence/military, electronics, research and development, medical, sensor and instrumentation, communications, and energy industries. Some the advantages of laser beam welding include deep penetration, narrow weld areas,minimal heat affected zones, low distortion, and excellent weld quality due to the non-contact laser beam welding process.

Written by Brian Chalmers

Ed

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