Gas Metal Arc Welding (GMAW)
GMA – commonly referred to as Metal Inert Gas (MIG) – welding embraces a group of arc welding processes in which a continuous electrode (the wire) is fed by powered feed rolls (wire feeder) into the weld pool. An electric arc is created between the tip of the wire and the weld pool. The wire is progressively melted at the same speed at which it is being fed and forms part of the weld pool.
Both the arc and the weld pool are protected from atmospheric contamination by a shield of inert (non-reactive) gas, which is delivered through a nozzle that is concentric with the welding wire guide tube.
Operation
MIG welding is usually carried out with a handheld gun as a semi-automatic process. The MIG process can be suited to a variety of job requirements by choosing the correct shielding gas, electrode (wire) size and welding parameters. Welding parameters include the voltage, travel speed, arc (stick out) length and wire feed rate. The arc voltage and wire feed rate will determine the filler metal transfer method.
This application combines the advantages of continuity, speed, comparative freedom from distortion and the reliability of automatic welding with the versatility and control of manual welding. The process is also suitable for mechanised set-ups, and its use in this respect is increasing.
MIG welding can be carried out using solid wire, flux cored, or a copper-coated solid wire electrode. The shielding gas or gas mixture may consist of the following:
- Argon.
- Carbon dioxide.
- Argon and carbon dioxide mixtures.
- Argon mixtures with oxygen or helium mixtures.
Each gas or gas mixture has specific advantages and limitations. Other forms of MIG welding include using a flux cored continuous electrode and carbon dioxide shielding gas, or using self- shielding flux cored wire, requiring no shielding.
