Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt and join.
The primary advantage of MIG welding is that it allows metal to be welded much more quickly than traditional "stick welding" techniques. This makes it ideal for welding softer metals such as aluminum. When this method was first developed, the cost of the inert gas made the process too expensive for welding steel. Over the years, the process has evolved, however and semi-inert gases such as carbon dioxide can now be used to provide the shielding function which now makes MIG welding cost-effective for welding steel.
Besides providing the capability to weld non-ferrous metals, MIG welding has other advantages:
It produces long, continuous welds much faster than traditional welding methods.
Since the shielding gas protects the welding arc, this type of welding produces a clean weld with very little splatter.
It can be used with a wide variety of metals and alloys.
The equipment is quite complex as MIG welding requires a source of direct current, a constant source and flow of gas, as well as the continuously moving wire electrode. Plus, electrodes are available in a wide range of sizes and are made from a number of metal types to match the welding application.
The actual technique used is different from traditional welding practices, so there is learning curve associated with MIG welding, even for experienced welders. For example, MIG welders may need to push the welding puddle away from them and along the seam.
The necessity for the inert gas shield means that MIG welding cannot be used in an open area where the wind would blow away the gas shield unless other precautions are taken to prevent this.
Since its development in the middle of the 20th century MIG welding has become commonplace in many manufacturing operations.
MIG can be used automatically or semi-automatically. An example of automatic MIG is a robotic arm welding car frames at an auto assembly plant. Semiautomatic is when an operator holds the MIG gun and manipulates the weld pool.
In automatic MIG, an operator sets up and watches the machine. An experienced welder is the preferred operator, because he has the right touch and knows what it means to be in the welding zone. In the zone is when you become one with the process of the weld metal becoming one with the base metal, grasshopper. In other words, you are seeing that you're putting down a good bead as you weld. Anyone can run a bead. A good welder sees the bead tie-in and makes sure it is uniform.