Page 68 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Welding Processes

Applications
Common uses of MMA are welding of pipelines, nozzles and
nodes and medium to heavy fabrications. MMA is com-
monly used outdoors owing to the good gas shielding
supplied from the melting flux.
Typical defects
Typical defects include slag inclusions, porosity, undercut,
lack of fusion and profile defects.
Metal inert gas (MIG)/metal active gas (MAG)/gas
metal arc welding (GMAW)
Process description
Figure 5.4 shows the equipment. An electric arc is struck
between a continuously fed consumable solid electrode wire
and the workpiece. The arc is protected by a shielding gas,
which can be either inert or active, depending on the material
being welded (Fig. 5.5). An inert gas such as argon or helium
does not affect the weld pool properties but an active gas
such as CO 2 does have an effect. MIG is known as a semi-
automatic process because the welding wire is continually fed

Figure 5.4 MIG welding equipment

53

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200905QG Welding chap5.3d Page 53 of 66