- Plasma welding is a well-known arc welding technique in which a gas jet is ionized by means of an electric arc. Two electric circuits are included: a) Pilot-arc-An electric arc is generated between a W electrode and a Cu nozzle, with an ionized high quality inert-gas (usually Ar). The efficiency of the arc is low, but it is useful for nonconducting materials. b) Transferred-arc-The electric arc is transferred from the W electrode to the welded material. The plasma-jet is accelerated towards the material causing local fusion. A high flow-rate shielding gas (Ar-H2 mixture) contributes to the protection of the weld material, improving the weld quality.