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Thermadyne S.A. Welding Information
Bulletin #13

Gas Metal Arc Welding (GMAW):- 
Metal Inert / Active Gas Welding (M.I.G. - M.A.G.)

Gas Metal Arc Welding (GMAW) (M.I.G. – M.A.G.) Process

Gas metal arc welding, commonly known as M.I.G. welding, consists of various components as indicated in the drawing above. The system uses continuous small diameter solid wire and an externally supplied gas or mixtures of gasses. The shielding gas can be Helium, Argon, Carbon dioxide or mixtures thereof.

M.I.G. – M.A.G. welding is suitable for use on all major commercial metals i.e. Low Carbon, Low and High Alloy Steels, Stainless Steels, High Strength quenched and tempered steels, Aluminium, Magnesium, Copper, Titanium, etc. With these various metals the welding techniques and weld procedures may vary widely.

Carbon – Dioxide or Argon – Oxygen (ACTIVE) mixtures are suitable as shielding gasses on low carbon and low alloy steels, whereas pure (INERT) gas (Argon – Helium) is used when welding high alloyed steels and alloys of Aluminium, Magnesium, Copper, Titanium, Stainless Steel and the Nickel Based alloys.

Welding is either semi-automatic, using a hand-held torch (manual) through which the wire is fed automatically, or fully-automatic equipment can be used.

Metal transfer achieved using the M.I.G. – M.A.G. process is done by one of two methods, namely, “spray arc” or short circuiting (globular). With spray arc, drops of molten metal detach from the wire and move through the arc column to the workpiece. With the short circuiting method, metal is transferred to the workpiece when the tip of the wire contacts the molten metal.

In short – circuit welding (globular), lower current, low voltages and small diameter wire is used and the metal is transferred with each short – circuit rather than across the arc as in spray arc welding. This method results in low heat input with the minimum of distortion and used on thin or poor fit-ups and bridging wide gap applications.

Spray arc M.I.G. welding produces a very hot, high voltage arc and gives a higher deposition rate than short circuit welding. The spray arc method is normally recommended for thicker sections requiring heavy single or multi-pass applications where deposition rate is important.

Gas Metal Arc (M.I.G. – M.A.G.) welding is done with Direct Current (D.C.) rectifier power sources, using reverse polarity, wire positive (+) and this provides a stable arc, smooth metal transfer, relatively low spatter loss and good weld bead.

Some M.I.G. – M.A.G. equipment also provides Spot Welding features that can assist with poor fit-ups or on thicker materials.

Problem Solving & Maintenance on M.I.G. – M.A.G. Welding Systems

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