The effect of welding speed and contact-tip-to-workpiece distance on the microstructural homogeneity and bead profile of Tandem GMA steel welds

Automated tandem gas metal arc welding (T-GMAW) has been identified as a welding system potentially capable of increasing productivity and minimising distortion in the fabrication of ship panels. The T-GMAW process was used in pulse-pulse mode on 6 mm plain carbon steel plate to determine the effect of welding travel speed (WTS) (1.0-2.0 m/min) and contact-tip-to-workpiece distance (CTWD) (20-35 mm) on weld metal microstructure and bead profile. In this mode, the leading and trailing welding wires alternately transfer metal into a single molten weld pool at welding travel speeds much greater than those used in conventional single-wire gas metal arc welding (GMAW). The results show that for the bead-onplate (BOP) welding of 6 mm plain carbon steel plate, adequate weld pool mixing and an acceptable level of microstructural homogeneity in the solidified weld metal were achieved for all welding conditions. BOP welding tests were also undertaken on 20 mm plain carbon steel plate which results in a greater weld cooling rate compared with the thin 6 mm plate. In the 20 mm plate, a relatively homogenous weld metal microstructure was also present, but there was evidence of limited weld pool mixing. Also, in-situ analysis of the arcs during welding and post test characterisation of the BOP samples showed that arc stability and bead profile are sensitive to both CTWD and WTS.