Welding MIG
In GMAW the arc is struck between the filler wire and the workpiece
The uncovered filler wire is automatically fed through the centre of the gun. The shielding gas is supplied through the gun and surrounds the arc pool during welding, thus protecting the weld from the atmosphere. The gas usually consists of argon with an added 1-2% oxygen or of pure argon.
A distinction is drawn between spray-arc welding and short-arc welding. The latter method is suitable for welding light-gauge sheet as well as for welding root beads in heavier material. It is also suitable for position welding. This process takes place at a lower voltage and current than in the case of spray-arc welding. A thin filler wire (0.8 mm) is used. The arc is short, hence the name, and metal transfer is in the form of big drops shortcircuiting the arc. This provides rapid alternation between arc heating and resistance heating.
By contrast, in spray-arc welding, the metal is transferred in the form of a fine mist of droplets which do not short-circuit the arc. The process, which derives its name from this feature, is suitable for material thicknesses of 3 mm and upwards.
The GMAW process is either semi-automatic or fully automatic. In many cases, it is more economical than welding with covered electrodes. However, all gas-shielded processes are sensitive to draughts. Thus, they are not suitable for outdoor work or for welding in open vessels in which a chimney effect may easily occur.
