Gas metal arc welding (GMAW) - Metal inert gas (MIG) and metal active gas (MAG) welding
GMAW or MIG/MAG is a semi-automatic process in which a metal arc burns between a current carrying wire electrode and the workpiece, protected by a shielding gas . The wire is fed mechanically into the arc by a wire drive unit with rollers.
Argon, helium or mixtures of these inert gases are used as shielding gas in the MIG process. Shielding gases of argon with the addition of oxygen, helium with the addition of oxygen, carbon dioxide (CO2) or mixtures of these gases are used in the MAG process. The shielding gas promotes the creation of a stable arc and protects the molten weld pool from coming into contact with the atmospheric air. The addition of oxygen to the shielding gases reduces the surface tension of the weld pool and leads to the formation of a flatter weld surface with good wetting onto the weld edges. The transfer of metal in the arc also becomes finer.
Excessive alloying of the wire electrodes equalizes the burn-off of alloying elements which occurs. It is imperative that the welding area is free from draughts. At high welding speeds and rapid oscillation, care must be taken to ensure complete shielding of the molten weld pool by using appropriate quantities of shielding gas and correct nozzle shapes.
Only direct current inverters or rectifiers are suited as as power sources, with the positive pole mainly on the electrode. Although welding with the negative pole increases the metal deposition efficiency, droplet transfer is higher and the arc less steady. Welding can be in the spray-arc or short arc mode, depending on welding current and arc voltage.
