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Process Schematic Diagram for MIG/MAG, FCAW and MCAW
Gas hose
Gas cylinder
Power source
Return cable
6.3 Introduction to Metal Cored Arc
Welding (MCAW)
How it Works
Metal-cored arc welding (MCAW) uses the heat
generated by a DC electric arc to fuse metal in
the joint area, the arc being struck between a
continuously fed consumable filler wire and the
workpiece, melting both the filler wire and the
workpiece in the immediate vicinity. The entire arc
area is covered by a shielding gas, which protects
the molten weld pool from the atmosphere.
As MCAW is a variant of the MIG/MAG welding
process there are many common features between
the two processes, but there are also several
fundamental differences.
As with MIG/MAG, direct current power sources
with constant voltage output characteristics are
normally employed to supply the welding current.
With metal-cored wires the terminal the filler
wire is connected to depends on the specific
Continuous wire
Wire feed unit
Power cable
Torch conduit
product being used, some wires designed to run
on electrode positive, others preferring electrode
negative, and some which will run on either. The
work return lead is then connected to the opposite
terminal. Electrode negative operation will usually
give better positional welding characteristics.
The output characteristics of the power source
can have an effect on the quality of the welds
produced.
The wire feed unit takes the filler wire from a spool
or bulk pack, and feeds it through the welding
torch, to the arc at a predetermined and accurately
controlled speed. Normally, special knurled feed
rolls are used with metal-cored wires to assist
feeding and to prevent crushing the consumable.
Unlike MIG/MAG, which uses a solid consumable
filler wire, the consumable used in MCAW is
of tubular construction, an outer metal sheath
being filled entirely with metal powder except
for a small amount of non-metallic compounds.
These are added to provide some arc stability and
de-oxidation.
Welding torch
Arc
Workpiece
Earth clamp
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