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PAW is an arc welding process that melts and joins metals by heating them with a constricted arc established between a tungsten electrode and the metals, as shown in Figure 1.15. It is similar to GTAW, but an orifice gas as well as a shielding gas is used. As shown in Figure 1.16, the arc in PAW is constricted or collimated because of the converging action of the orifice gas nozzle, and the arc expands only slightly with increasing arc length [5]. DCEN is normally used, but a special variable‐polarity PAW machine has been developed for welding aluminum, where the presence of tenacious aluminum oxide films prevents a keyhole from being established.

Figure 1.15 Plasma arc welding: (a) overall process; (b) welding area enlarged and shown with keyholing.

Figure 1.16 Comparison between a gas–tungsten arc and a plasma arc [5].

Source: Welding Handbook, Vol. 2, 7th Edition, © American Welding Society.