Conventional TIG/GTAW is a melt-in process. Surface tension causes the molten metal to circulate, moving the heat first to the sides and then flowing to the bottom of the weld pool, before returning to
Plasma Arc Welding (PAW) was developed in the 1960’s, and until recently was the only practical choice where deep penetration welds were required. While good quality welds can be achieved, the practical upper limit for full penetration PAW welding is 8 - 10mm (5/16 to 13/32 inch), and is more typically used for root passes of 4-6mm (5/32 to 1/4 inch) followed by filler passes using TIG.
MIG/GMAW is a welding process in which an electric arc forms between a consumable wire electrode and the joint, which heats the workpiece metals, causing them to melt and join. GMAW is a low penetration process which requires extensive edge preparation and consumption of filler material.
Submerged Arc Welding is a process which requires a continuously fed, consumable, solid or tubular (metal cored) electrode. The molten weld is protected from atmospheric contamination by being ‘submerged’ under a blanket of granular flux consisting typically of lime, silica, manganese oxide, calcium fluoride and other compounds.