Waveform analysis for MIG / GMAW "Lincoln RapidArc" on steel

These welds were performed on 5mm steel plate with 1.2mm diameter steel MIG wire and Ar/20%CO2 shielding gas.

All traces are for Lincoln Electric's "RapidArc" - a variant of Pulse-GMAW claimed to give stable welding at fast run rates.

Sampling rate for all data-logging shown here is 20kHz.

Review of comments here, 18 June 2011

I will not be re-writing these notes, but several comments are misguided.

It is clear that I have identified "pure pulse" as the "nice" condition. That's the "200/1.30" condition. "RapidArc" is gone, becoming "pulse transfer" as generally understood. The "420/1.20" condition has little of "RapidArc" left.

I know now that there is intended to be a "dipping" event, which can be seen where the voltage goes to a low value presumably representing the voltage drop of the Ohmic resistance of the wire bridging between contactor tip and weld pool. The "dipping" ("shorting") event happens at low current always. So as I do credit at the time, it results in no spatter. It is clear the brochure description of "RapidArc" is compatible with the waveform measured. The second small current peak does indeed look to be designed to depress the weld-pool away from the wire when the short-circuit breaks, as claimed in the brochure(s).

Trying welding again - doing a T-fillet weld on 6mm plate using 1.2mm wire, example conditions giving excellent results were