MIG

GMAW OR MIG (Metal inert gas welding):

Sometimes this process is refers as MAG (Metal active gas welding).

GMAW is a arc welding process in which an electric arc forms between a consumable wire electrode and the work piece.

Along with the wire a shielding gas also feed through the welding torch to protect the weld tool from atmospheric contamination.

This process can be automatic or semi-automatic.

MIG welding can be used to weld steels, aluminium alloys, copper alloys(not with high zinc), magnesium alloys. It is suitable for position welding but works best in downhand position.

The deposit efficiency is much higher than in manual arc welding with a very small amount of slag.

MIG Welding however requires a more expensive power source than MMAW. Normally constant voltage power source is used. The equipment is also less portable.

Since the welding gun has to be close to the job, the process is less adaptable than SMAW in difficult to reach access.
Shielded gases plays a vital role in MIG Welding, it prevents the welding bead from atmospheric gases e.g. nitrogen and oxygen, which may causes porosity, fusion defects, and weld metal embrittlement if they come in contact during welding.

Required Equipment for MIG:

• Power source
• Electrode
• Shielding gases
• Welding gun Or wire feeder unit 

These are the basic requirements, except this operator should take acre of necessary PPE`s.

From quality point of view two most common quality issue are there First is DROSS and second is POROSITY. During welding process if they are not in control of operator then they lead weaker weld, less ductile, and slag inclusion. In order to prevent weld bead should be clean by wire brush and perfect control on gap.

Second is porosity because of gas entrapment in weld pool, which occurs when the metal solidify before gases escape from there. It may because of impurities in shielding gases or work piece or arc length variation.
And the cooling rate is related to gases entrapped.