Comparing CW-GMAW in direct current electrode positive (DCEP) and direct current electrode negative (DCEN)

Abstract

Gas metal arc welding (GMAW) with direct current electrode negative (DCEN) can offer some advantages over direct current electrode positive (DCEP) welding, such as a higher electrode melting rate and lower heat input imposed onto the workpiece. Despite these advantages, DCEN is not commonly used in field applications due to instabilities caused by arc climb and the volatile repelled metal transfer mode across the arc. This work reports a comparison between DCEP and DCEN in natural spray transfer mode using a welding power source operating in constant voltage (CV). It aims to assess the feasibility of DCEN in cold wire gas metal arc welding (CW-GMAW) comparing the results obtained in DCEN with previous results obtained in DCEP for the same welding parameters. During experiments, the current and voltage were acquired with synchronized high-speed video to study the arc dynamics. Bead-on-plate welds were deposited onto AISI 1020 steel flat bars. Three cross sections for each bead were cut and metallographically examined to compare bead geometry. Results suggest that the cold wire feeding can suppress arc climb in DCEN welding, consequently improving the arc stability and bead finish. Moreover, the DCEN welds suggest that the heat transferred to the weld pool is fundamental to accommodate high feed rates of cold wire. Lastly, the cross section results show that penetration, dilution, and HAZ area are lower in DCEN than in DCEP mode.