Effect of welding parameters on the working envelopes for plasma arc welding

The working envelopes for plasma keyhole welding, which were confined by various combinations of plasma gas flow rate (PGFR), travel speed, and welding current, have been established. Welding parameters chosen within these envelopes represent that sound welds could be obtained. Welding outside the envelopes would result in welding defects such as intrinsic undercut and underfill in the welds or an unstable keyhole during the process. Conditions for the double (twin) arc formation were also studied. The results indicate that the welding voltage, in general, increased with increasing arc length, welding current, and PGFR. The critical current (Ic), defined as the welding current beyond which double arc forms and the corresponding welding voltage drops, had a maximum value at PGFR of 0.24 Ipm (0.5 cfh). However, a PGFR of at least 0.76 Ipm (1.6 cfh) was required for the keyhole welding of 3.2 mm thick 410 stainless steel. No apparent correlation of the critical current and arc length was observed. The influe...