GMAW (Gas Metal Arc Welding) al so call MIG (Metal Inert Gas) if the shielding gas is inert, for example argon, or MAG (Metal active gas) if the gas has a content of an active gas such as CO2. In Europe the process is usually called MIG/MAG or just MIG welding.
The process is used in a wide range of plate thinknesses even though it has been most dominant in thin sheet welding. This is because of its easiness in starting and stopping and thereby its relatively high productivity. Compared to stick electrode (MMA) welding there is no need for frequent electrode changes and slag removal.
The principla of MIG welding is that a metallic wire is fed through the welding gun and melted in an arc. The wire serves the dual purpose of acting as current-carrying electrode and as the weld metal filler wire. Electrical energy for the arc is supplied by a welding power source. The arc and the pool of molten material are protected by a shielding gas, which is ether inert or active. In this context, an inert gas is one that does not react with the molten material. Examples of gases in this category are argon and helium. Active gases, on the other hand, participate in the processes in the arc and the molten material. Argon containing a small proportion of carbon dioxide or oxygen is an example of an active gas.
In order to achieve optimum welding performance, it is important that the welding parameters are set correctly. Examples of such parameters in MIG welding are voltage, wire feed speed and the shielding gas flow.
The process of MIG / MAG welding is a continuous wire process where the electric arc strikes between fuse wire and workpiece; the protection of the weld pool is ensured by a shielding gas, which flows from the torch to the workpiece that should be welded. As it is a continuous wire process, an high productivity is ensured to the process, at the same time the presence of gas allows to operate without slag (both features increase the cost efficiency of the process if compared to electrode welding).
On the other side, a MIG / MAG welding station is necessarily composed of the following components:
1. Torch: it carries the wire, current and gas directly into the welding bath;
2. Earth cable;
3. Arc current generator (transformer or inverter);
4. Feeder mechanism and wire control;
5. Extension lead cables/pipes: it connects the generator to the wire feeder mechanism;
6. Reel winders;
7. Tank of shielding gas.
Thanks to continuous wire, it is possible to get current densities higher than those of covered electrodes, which means more penetration, more productivity and hence fields of application. MIG / MAG welding procedures is a process derived from a submerged arc, but compared to the latter. it has the advantage that the operator can control directly the arc and therefore check the welding as during covered electrode and TIG processes. Further advantages, compared to the submerged arc, are the lack of slag formation and the possibility of welding in non-flat positions.
MIG / MAG welding is used when high productivity and an adequate application flexibility are necessary. Thanks to this technology is possible to weld carbon steels, stainless steels, light-alloys metals (Al, Mg), copper alloys, nickel alloys and titanium alloys. It finds application in every metallurgical area. As the protection of the welding pool is ensured by a gas flow, this procedure is recommended mainly workshops, because in open spaces just a light wind can waste the shield gas flow with consequent low quality of the welded joint.