page_title: Gas metal arc welding
section_title: Welding gun and wire feed unit
hierarchical_section_title: Gas metal arc welding / Equipment / Welding gun and wire feed unit
caption_attribution_description: English: GMAW on Stainless Steel
context_page_description: Gas metal arc welding, sometimes referred to by its subtypes metal inert gas welding or metal active gas welding, is a welding process in which an electric arc forms between a consumable MIG wire electrode and the workpiece metal, which heats the workpiece metal, causing them to melt and join. Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from atmospheric contamination.
  The process can be semi-automatic or automatic. A constant voltage, direct current power source is most commonly used with GMAW, but constant current systems, as well as alternating current, can be used. There are four primary methods of metal transfer in GMAW, called globular, short-circuiting, spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and limitations.
  Originally developed in the 1940s for welding aluminium and other non-ferrous materials, GMAW was soon applied to steels because it provided faster welding time compared to other welding processes. The cost of inert gas limited its use in steels until several years later, when the use of semi-inert gases such as carbon dioxide became common.
context_section_description: The typical GMAW welding gun has a number of key parts—a control switch, a contact tip, a power cable, a gas nozzle, an electrode conduit and liner, and a gas hose. The control switch, or trigger, when pressed by the operator, initiates the wire feed, electric power, and the shielding gas flow, causing an electric arc to be struck. The contact tip, normally made of copper and sometimes chemically treated to reduce spatter, is connected to the welding power source through the power cable and transmits the electrical energy to the electrode while directing it to the weld area.  It must be firmly secured and properly sized, since it must allow the electrode to pass while maintaining electrical contact. On the way to the contact tip, the wire is protected and guided by the electrode conduit and liner, which help prevent buckling and maintain an uninterrupted wire feed. The gas nozzle directs the shielding gas evenly into the welding zone. Inconsistent flow may not adequately protect the weld area. Larger nozzles provide greater shielding gas flow, which is useful for high current welding operations that develop a larger molten weld pool.  A gas hose from the tanks of shielding gas supplies the gas to the nozzle. Sometimes, a water hose is also built into the welding gun, cooling the gun in high heat operations.
  The wire feed unit supplies the electrode to the work, driving it through the conduit and on to the contact tip.  Most models provide the wire at a constant feed rate, but more advanced machines can vary the feed rate in response to the arc length and voltage.  Some wire feeders can reach feed rates as high as 30 m/min (1200 in/min), but feed rates for semiautomatic GMAW typically range from 2 to 10 m/min (75 – 400 in/min).
caption: GMAW on stainless steel
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