Metal Inert Gas (MIG) welding, also known as gas metal arc welding (GMAW), is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun. A constant voltage, direct current power source is used mostly, but constant current systems, as well as alternating current, can be used. There are four primary methods of metal transfer in TIG welding: globular, short-circuiting, spray, and pulse-spray, each of which has distinct properties and corresponding advantages and limitations. Originally developed for welding aluminum, it also includes steels because it allows for lower welding time compared to other processes. Today, MIG welding is the most common industrial welding process, preferred for its versatility, speed, and the relative ease of adapting the process to robotic automation. The automobile industry uses the MIG welding process almost exclusively. Unlike welding processes that do not employ a shielding gas, it is rarely used outdoors. This method is often used in arc spot welding, thereby replacing riveting or resistance spot welding.