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MIG is a form of arc welding where a wire is continously fed into the welding gun, where it becomes the electrode and melts into the weld pool. A much smaller electrode wire is used compared to arc welding, and a roll of the electrode wire is fed into the weld pool. A shielding gas is also injected around the arc to keep out contaminants.
This process is also referred to as metal inert gas welding. Power is usually supplied by a direct current, constant-voltage power supply, but AC or constant current systems can also be used.
MIG is a versatile process that works well on a
variety of metals, including steel, stainless steel, alumnium, and other
non-ferrous metals. MIG welding is currently the most common form of industrial
welding, and is used in a variety of industries, from ship building to welding
race car and motorcycle frames.
The advantages of MIG welding are its versatility, relative ease of use, and the
speed of the process, especially when compared to TIG welding. MIG also lends
itself to robotic automation, and is widely used in automobile assembly lines,
among other industries.
MIG welding does have some drawbacks, however. Because the technique uses a
shielding gas to protect the weld area from contamination, it is rarely used
outdoors (because of wind) or indoors where the air is unstable. But be aware
that you will need some ventilation when welding, and you never want to inhale
the shielding gas. Argon can be harmful or even fatal if inhaled over any length
of time.
Mig welders are available in several types, including models for manual manipulation, or semiautomatic welding. There are also models for automatic or machine welding, depending on the the application (and your budget).
Due to the fact that on a Mig welder, the electrode is continuously fed, the welding gun has to have a sliding electrical contact in order to transmit the welding current to the electrode. The gun also needs a nozzle and a gas passage in order to direct the shielding gas top an area around the welding arc and the weld pool. This shielding gas is the primary reason that Mig welding is usually done indoors or in controlled environments where wind won't be a problem.
Another concern is cooling the welding gun due to the tremendous heat generated by the arc welding process. Most guns use either water circulated internally, or the shielding gas itself, for cooling.
When Mig welding, you'll also want to match your wire type to the metal being welded. For thin metals, use a smaller diameter wire. For thicker metals, use a larger diameter wire (and a more powerful welder). You'll also want to choose a wire to match the base metal to be welded. As in steel wire for welding steel, aluminum wire for welding aluminum, etc.
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