Gas Metal Arc Welding (GMAW ) is also some time referred as Metal Inert Gas (MIG ) welding is an arc welding process in which a continuous solid wire electrode is heated fed through a welding gun and into the weld pool, joining the two base materials together. A shielding gas ( CO2 or Argon ) is also sent through the welding gun and protects the weld pool from contamination. When we welding aluminum than we are using argon as the shielding gas, and for carbon steels using CO2. CO2 and Ar-CO2 mixtures are known as metal active gas (MAG) processes. MIG is an attractive alternative to MMA welding, offering high deposition rates and high productivity. MIG / MAG welding is a versatile technique suitable for both thin sheet and thick sheet.
Manual MIG/MAG welding is often referred as a semi-automatic process, as the wire feed rate and arc length are controlled by the power source, but the travel speed and wire position are under manual control. The process can also be mechanised when all the process parameters are not directly controlled by a welder, but might  still require manual adjustment during welding. When no manual intervention is needed during welding, the process can be referred to as automatic.
The process usually operates with the wire positively charged and connected to a power source delivering a constant voltage. Selection of wire diameter (usually between 0.6 and 1.6mm) and wire feed speed determine the welding current, as the burn-off rate of the wire will form an equilibrium with the feed speed.