Page 74 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Welding Processes

Typical defects
Porosity, lack of fusion defects (particularly in the short-
circuiting mode), solidification cracking in the spray mode
and crater pipes are typical defects.
Flux-cored arc welding (FCAW)
Process description
The equipment is similar to MIG/MAG but uses a flux-cored
wire (Fig. 5.7). An arc is formed between a continuously fed
tubular electrode wire containing a flux and the work. The
arc is protected by a gaseous shroud formed by the flux
melting. An external secondary shielding gas can also be
supplied through the torch (Fig. 5.8). Using a flux-cored wire
enables the addition of alloying elements and the production
of a shielding gas more tolerant to outdoor use than MIG/
MAG. This means that the benefits of the MMA process can
be combined with the speed of the MIG/MAG process. The
downside is that it requires slag removal between runs, a
backing material for root runs and suitable equipment to
remove the large volumes of fume produced from the self-
shielding process.
Polarities
DCEP or DCEN is dependent on the wire being used. The
power source has a ‘flat’ or constant voltage characteristic
(Fig. 5.6).
Consumables
Cored wires may be self-shielded or gas shielded. Gases may
be CO 2 , Ar/CO 2 mixtures or Ar/O 2 mixtures. The Ar/O 2
mixture is often used to replace Ar/CO 2 to keep carbon levels
at a minimum when welding stainless steels or high alloy
materials.
Applications
This process is used in shipyards, structural applications, and
other medium and heavy fabrications where positional
welding would not be possible with solid wire welding.

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200905QG Welding chap5.3d Page 59 of 66