Plasma arc welding is a welding method using plasma arc as heat source.The gas is dissociated by arc heating and compressed when it passes through the water cooling nozzle at high speed, which increases the energy density and dissociation degree and forms a plasma arc.Its stability, calorific value and temperature are higher than those of ordinary arc, so it has higher penetration force and welding speed.Argon is generally used for the gas forming the plasma arc and the protective gas around it.According to the material properties of various workpieces, argon, hydrogen and other mixed gases are also used.