Page 72 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Welding Processes

the spray mode for one second, giving deep penetration, but
then reduce the amps/volts for one second to allow the weld
pool to reduce in size before increasing back up to the spray
mode, and so on. In this way the likelihood of getting a lack
of fusion-type defects found with the short-circuiting mode is
reduced.
Consumables
The only consumables used in a MIG/MAG process are solid
wires between 0.6 and 2.4 mm and gases consisting of argon,
helium, argon/helium mixtures, CO 2 , Ar/CO 2 mixtures, Ar/
O 2 mixtures or other proprietary mixtures. It is worth noting
the following points in relation to gases:
. Pure CO 2 can be used with steels 4 0.4% C and low alloy
steels using triple deoxidised wire, but it is not usually used
in the spray mode.
. Argon produces a better arc in the spray mode and is
better with non-ferrous metals and alloys.
. Ar/O 2 (1 or 2%) mixtures are used for stainless steels.
. Helium is normally mixed with argon, oxygen or CO 2 . The
higher helium contents produce higher arc voltages and
heat inputs and give deeper penetrating welds with higher
welding speeds.
. Argon/CO 2 (5 to <20%) mixtures are normally used to
give a combination of good penetration, a stable arc, less
spatter and a flatter weld profile. The lower 5% CO 2 is
used in the spray mode and the higher 20% CO 2 is used in
the short-circuiting mode. The higher CO 2 level is required
to give better penetration in what is a low heat input
transfer mode.
Applications
MIG/MAG is commonly used for the welding of structural
steels, aluminium alloys and stainless steels. It combines
good weld properties with fast deposition rates in light,
medium and heavy fabrications.

57

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200905QG Welding chap5.3d Page 57 of 66