Penetration effects of the compound vortex in gas metal-arc welding

Abstract

Twenty-one constant current welds were made at DCRP currents from 204 to 358 A. Three experiments were conducted where the current was in the form of a very slow sawtooth waveform from 200 A to 380 A over a period of 50 seconds. Two low frequency pulsed current welds were made using a 650 A peak current and a Hz. All welds were made bead on mild steel plate using constant current GMAW equipment and argon + 2% oxygen shielding gas. After welding, the plates were cut, ground, polished and etched with 12% nital solution to show depth of penetration. The constant current welds showed that unlike its behavior in GTAW, penetration increases gradually over the current range tested. Also, the growth of the finger constituted nearly all of the total penetration increase indicating convective flows of increasing magnitude. The ramped current experiments reinforced the observation that penetration increases gradually over the current range examined. The weld pool was also observed to fluctuate, slightly depress and finally depress significantly as the compound vortex started to form, formed completely and then grew stronger. The low frequency pulsed gas metal arc welds realized very little penetration because the wire feed motor was not fast enough and the torch had to be raised causing severe arc spreading. (aw)