Page 13 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

A 10 Minute Guide

Here are some frequently asked questions about welding
inspection subjects. You can answer them if you spend ten
minutes reading the following information.
1. What is the difference between the main
welding processes? (four minutes)
MMA has an arc struck between a consumable flux-coated
electrode and the workpiece. The electrode melts and fills the
joint with weld metal. The flux coating melts and produces
gas to shield the arc. The melted flux also helps to remove
impurities from the weld and forms a layer of slag on top of
the weld. This slag must be removed between runs or it can
cause slag inclusions within the weld. This is the most
commonly used outdoor site welding process.
MIG/MAG has an arc struck between a reel-fed consumable
solid wire electrode and the workpiece. It does not produce
slag because the arc is shielded by an inert gas (active gas for
MAG). It deposits weld metal quickly and can be used semi-
automatically, mechanized or automated. This process can
achieve fast weld metal deposition rates.
FCAW is similar to MIG/MAG but the consumable reel-fed
electrode is hollow with a flux contained inside. The arc can
be self-shielded using only the melting flux or a secondary gas
shield can be used. Slag will be produced and must be
removed between runs. Basically, this process gives a
combination of the advantages (and disadvantages) of
MMA and MIG/MAG.
TIG has an arc struck between a non-consumable tungsten
electrode and the workpiece. Filler in wire or rod form is
added separately. It does not produce slag because the arc is
shielded by an inert gas. It is a very slow process but
produces very high quality welds.

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200900QG Welding Prelims.3d Page 12 of 14