MIG (Metal Inert Gas welding) At first Gas Metal Arc Welding (GMAW) was considered to be, fundamentally, a high current density, small diameter, bare metal electrode process using an inert gas for arc shielding. Its primary application was for welding aluminum. As a result, the term MIG (Metal Inert Gas) was used and is still a common reference for the process. Subsequent process developments included operation at low current densities and pulsed direct current, application to a broader range of materials, and the use of reactive gases (particularly CO2) and gas mixtures. This latter development has led to the formal acceptance of the term gas metal arc welding (GMAW) for the process because both of inert and reactive gases are used. GMAW (MIG) may be operated in semiautomatic machine or automatic modes. All commercially important metals such as carbon steel, high-strength low alloy steel, stainless steel, aluminum, copper, titanium, and nickel alloys can be welded in all positions with MIG process by choosing of the appropriate shielding gas, electrode, and welding variables. Uses and advantages of MIG: • MIG (GMAW) is the only consumable electrode process that can be used to weld all commercial metals and alloys. • MIG (GMAW) overcomes the restriction of limited electrode length encountered with shielded metal arc welding. • MIG welding can be done in all positions, a feature not found in submerged arc welding. • MIG depositions rate are significantly higher than those obtained with shielded metal arc welding. • Welding speeds are higher than those with shielded metal arc welding because of the continuous electrode feed and higher filler metal deposition rates. • In MIG process the wire feed is continuous, long weld can be deposited without stops and starts. • When spray transfer is used, deeper penetration is possible than with shielded metal arc welding, which may permit the use of smaller size fillet welds for equivalent strengths. • For MIG minimal postweld cleaning is required due to the absence of a heavy slag. These advantages make the MIG process particularly well suited to high production and automated welding applications. This has become increasingly evident with the advent of robotics, where MIG has been predominant process choice. Limitation of MIG • MIG welding equipment is more complex, more costly, and less portable than that for SMAW. • MIG is more difficult to use in hard to reach places because the welding gun is larger than a shielded metal arc welding holder, and the welding gun must be close to the joint (10-19 mm), to insure that the weld metal is properly shielded. • MIG welding arc must be protected against air drifts that will disperse the shielding gas. This limits outdoor applications unless protective shields are placed around the welding area.