Gas shielded welding is an arc welding method that uses external gas as a protective medium. Its advantages are good visibility of the arc and molten pool, easy operation; no slag or very little slag, and no need to remove slag after welding. However, special wind-proof measures must be taken when working outdoors.
According to whether the electrode is melted during the welding process, gas shielded welding can be divided into non-melting electrode (tungsten electrode) gas shielded welding and molten electrode gas shielded welding. The former includes tungsten inert gas welding, plasma arc welding and atomic hydrogen welding. At present, atomic hydrogen welding is rarely used in production.
Tungsten Inert Gas Welding is abbreviated as TIG (Tungsten Inert Gas Welding) welding. It is a welding method that uses the arc heat generated between the tungsten electrode and the workpiece to melt the base material and filler wire (if filler wire is used) under the protection of inert gas. During welding, the shielding gas is continuously sprayed from the nozzle of the welding torch, forming a gas protective layer around the arc to isolate the air to prevent its harmful effects on the tungsten electrode, the molten pool and the adjacent heat-affected zone, so as to obtain a high-quality weld. The shielding gas can be argon, helium or a mixed gas of argon and helium. In special applications, a small amount of hydrogen can be added. It is called argon tungsten arc welding which uses argon gas as the shielding gas, and that which uses helium gas is called tungsten helium arc welding. Because helium is expensive, the application of argon tungsten arc welding in industry is much wider than that of helium arc welding. This chapter takes argon tungsten arc welding as a typical example, introduces tungsten inert gas shielded welding, and in some places also explains the unique properties of helium and tungsten helium arc welding.