Whilst welding has been practiced in some form or other for centuries, MIG (Metalic Inert Gas) welding is a relatively new process. First used in the 1940's, it has one main advantage over both conventional gas welding and electric arc welding, namely that no flux is required. Standard electric arc welding is around six times faster than gas, but the fact that MIG welding requires no flux makes this process quicker still.
Based on the electric arc method, the electrode is a continuous length of welding wire, which is fed from a spool normally mounted overhead or on a motorised drum within the welder. The wire is then fed in at the desired rate to suit the welding speed. The welding area is shielded by an inert gas, usually argon or carbon dioxide, which is forced in to expel the oxygen present in the atmosphere. This is an important aspect of the whole process because it is the oxygen that causes a film of oxide on the metal. This is prevented in conventional welding by using flux. However, when welding is complete all traces of flux must be removed. This involves dipping the work in hot water, followed by caustic soda. Then it must be dipped in nitric acid and finally washed with cold water. It is a very time consuming process and it is here that the MIG method really scores over the conventional methods.
The equipment is relatively expensive, and more training and practice is required than for the conventional methods. However this is offset by the speed of the whole process and the fact that, once ground and polished, a good weld can be almost invisible. Especially suitable for aluminum, the MIG process is also used on stainless steel and, to a lesser extent, mild steel.
