Gas Metal Arc Welding (GMAW), sometimes referred to by its subtypes Metal Inert Gas (MIG) Welding or Metal Active Gas(MAG) Welding, is a Welding process in which an electric arc is formed between a consumable wire electrode and the work piece metal, which heats the work piece metal, causing them to melt and join. Along with the wire electrode, a shielding gas is fed through the welding gun, which shields the process from the contaminants in the air. The process can be semi-automatic or automatic. A constant voltage, direct current, power source is most commonly used with GMAW, but constant current systems as well as alternating current can be used.