Page 59 - Welding Robots Technology, System Issues, and Applications

Welding Robots
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a b c d

Figure 2.12. Cross section of common flux-cored electrodes. Solid electrode – a; flux-cored
electrodes – b, c and d

The main limitations of flux-cored electrodes are the large quantity of fumes
generated, which is potentially toxic, and the need for removing slag, particularly
in multipass welds. Flux–cored electrodes are more expensive than solid electrodes
but the difference in cost of the consumable is compensated by the decrease in
labor costs because they have higher burn-off rate than solid electrodes.

Flux-cored electrodes of 1 and 1.2 mm diameter can be used in positional work in
contrast to electrodes of 1.6, 2.4 and 3.2 mm that must be used in flat and
horizontal positions. In the last few years electrodes have been developed mainly
for welding carbon and low alloy steels as well as for stainless steels and for
hardfacing applications. For steels, CO 2 and argon/CO 2 mixtures are used as
shielding gases.

Constant-voltage direct current machines are recommended for FCAW processes,
though output rates should be higher than for conventional process. For semi-
automatic process outputs, between 400 and 600 A are recommended while for
mechanized and robotic systems power sources with outputs, up to 1000 A may be
required for some applications. Knurled feed rollers are generally used to feed
flux-cored electrodes in order to avoid crushing the electrode, even when using low
pressure. Water-cooled torches are used mainly in automatic and robotic welding
for currents above 300 A when argon-rich shielding mixtures are used.

MIG/MAG tandem and multi wire welding can give a significant increase in
welding speed and disposition rate and also influence the weld geometry [19].

The GMAW process can be used in combination with other welding processes
such as plasma arc welding (PAW) or laser welding (LW) to improve deposition
rate, welding speed, flexibility and productivity [20],[21]. Limitations of these
processes are the high capital cost and complexity in setting optimal welding
parameters.

The AC pulsed GMA process is currently under development for robotic welding
applications. It is well suited to the welding of aluminum alloys, giving high-
quality and productivity in welding of thin-sheet joints. Moreover it extends the
root opening tolerance and reduces work-piece distortion, during the welding cycle
[58].