A MIG welder is a welding machine that creates a heated arc that melts and fuses two pieces of metal.

Versatile and relatively easy to learn, MIG welding consists of a continuously-fed spool of wire and a welding gun fueled by an inert gas. The MIG (metal inert gas) welding process originated in the 1940s and has evolved into the most popular welding method in industrial applications.

How Does a MIG Welder Work?

• The wire, averaging about .030" in diameter, is fed through a copper contact tube that conducts the current into the wire.
• Shielding gas, fed through a nozzle around the wire, protects the weld pool from the surrounding atmosphere.
• The MIG welder contains a motor-driven reel that feeds the wire as the operator moves the welding gun along the joint line.
• Wires are often solid, but they could also be cored, which means they have a metal sheath surrounding either flux or metal filling.
• The wire acts as a heat source via the arc at the wire's tip and also as filler metal for the weld joint.
• Many MIG welders allow the operator to select the wire diameter and then dial in the metal's thickness, allowing the machine to automatically select the correct voltage and amperage, along with the speed of the wire-feed.

Compared with other welding processes, the consumables in MIG welding are relatively inexpensive. And because the wire is continuously fed, the MIG process lends itself to higher productivity, especially when compared to the frequent electrode changes required in stick welding.

Shielding Gases & MIG Welding

Shielding gases can be mixtures of argon, oxygen, CO2, and sometimes even helium, all depending on the material being welded. The gases' primary duty is to prevent the molten weld pool from being exposed to oxygen, nitrogen, and hydrogen in the surrounding air. These elements, if left unchecked, could result in excessive spatter and porosity.