Gas metal arc welding (GMAW), also known as metal inert gas (MIG) welding or metal active gas (MAG) welding is a semiautomatic or automatic arc welding process in which a continuous and consumable the wire electrode and a shielding gas are fed through a welding gun. Originally developed for welding aluminum and other nonferrous metals in the 1940s Gas metal arc welding was soon applied to other steels because it allowed for lower welding time compared to other welding processes. Developments during the 1950s and 1960s gave the process more versatility, and as a result it became a highly used industrial process.

The automobile industry in particular uses gas metal arc welding almost exclusively! Unlike welding processes that do not employ a shielding gas, such as shielded metal arc welding, it is rarely used outdoors. The electric arc was discovered and developed by Humphry Davy in 1800. C.L Coffin also had the idea of welding an inert gas atmosphere in 1890, but even in the early 1900, welding non-ferrous materials like aluminum and magnesium remained difficult.

To solve the problem, bottled inert gasses were used in the beginning of 1930. The electric arc process was perfected in 1941, and became known as heliarc or tungsten inert gas welding because it utilized a tungsten electrode and helium as a shielding gas. In 1953, a new process based on GTAW was developed, called plasma arc welding. It affords greater control and improves weld quality by using a nozzle to focus the electric arc, but is largely limited to automated systems, whereas GTAW remains primarily a manual, hand-held method.

Advantages of Mig welders:

1- Easy to learn
2- Welding can be done in all positions
3- High rate of filler metal deposition
4- Narrow weld bead
5- Creates clean, precise welds, resulting in higher quality welding
6- High welding speeds
7- Gaps filled or bridged easily
8- No stub loss
9- No slag

Books to read for more information on Mig Welding:
Welder's Handbook: A Complete Guide to Mig, Tig, Arc & Oxyacetylene Welding (Hp1264) by Richard Finch
Performance Welding Handbook (Motor books Workshop) by Richard Finch
Monster Garage: How to Weld Damn Near Anything (Motor books Workshop) by Richard Finch
The Complete Guide to Auto Body Repair (Motor books Workshop) by Dennis W. Parks
Metal Fabricator's Handbook by Ron Fournier

Websites to visit for more information on the TIG welder as well as other welders; Instructables, Carmen Electrode, Lincoln Electric and Miller Welds.

Best brands to look for; Hobart, Miller, Lincoln. Good luck in your search!