A MIG welder is a device that uses the Metal Inert Gas welding process to join pieces of metal. MIG welders are generally considered the easiest welding tool to use because the gas mixture used in the process is least likely to add contaminants to the weld.
MIG welding is a semi-automated process. The wire spool inside the welding device automatically feeds into the flame so that the person doing the welding only needs to focus on guiding the torch. Variables such as welding temperature, density of the gas shield and wire feed rate can be adjusted using controls on the welder.