Gas Metal Arc Welding (GMAW) is also known as Metal Inert Gas Welding (MIG welding). In this process, consumable electrode is used in the form of wire and an inert gas such as Argon, Helium, Carbon dioxide or a mixture of them are used. These inert gases shield the weld pool from atmospheric contamination. The shielding gas is allowed to flow through the weld gun. Electrode of MIG welding (which comes in wire form) is fed continuously, at a fixed rate, by a feeding mechanism. The wire is consumed during the process and thereby provides filler metal. This process is illustrated in the below Figure.
Selection of inert gas should be done with lots of care. A mixture of CO2 and Argon is considered as a good combination. 75% Argon + 25% CO2 (very popularly known as “75/25” or “C25”) works as the best “all purpose” shielding gas for carbon steel. It results in least amount of spatter and proper weld bead.
100% carbon dioxide yields deeper penetration, but extra caution needed since it may increase the amount of spatters.