Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
toughness. These changes are insufficient to affect the weld metal property
requirements for most applications, but may be significant in critical lowtemperature
and cryogenic joints.
In carbon steel wires, it has been found that excessively thick copper
coating can cause feedability problems, and it was feared at one time that
copper fumes from the coating might represent a health hazard. As a result
uncoppered wires became available. These wires give good feedability, by
virtue of a surface lubricant, and it has been demonstrated [51] that they can
reduce breathing zone fume levels. However, higher contact tip wear has
been suggested to be a potential problem. It is now common for copper
coating thickness to be controlled to a relatively thin layer and it has been
demonstrated that this overcomes fume and feedability problems.
4.4.2 Flux-cored wire
Flux-cored wires consist of a metal outer sheath filled with a combination of
mineral flux and metal powders (Fig. 4.3). The FCAW process is operated in
a similar manner to GMAW welding and the principle is illustrated in Fig.
4.4. The most common production technique used to produce the wire involves
folding a thin metal strip into a U shape, filling it with the flux constituents,
closing the U to form a circular section and reducing the diameter of the tube
by drawing or rolling.
The production process is illustrated diagrammatically in Fig. 4.5. The
seam is closed during the reduction process. Alternative configurations (Fig.
4.6) may be produced by lapping or folding the strip or the consumable may
be made by filling a tube with flux followed by a drawing operation to
reduce the diameter. Typical finished wire diameters range from 3.2 to
0.8 mm. Flux-cored wires offer the following advantages:
∑ high deposition rates;
∑ alloying addition from the flux core;
∑ slag shielding and support;
∑ improved arc stabilization and shielding.
Flux powder core
Outer metal sheath
4.3 Construction of a flux-cored wire.