Overcoming Physical Limits for High Speed GMAW on Thin Sheets

Overcoming physical limits for high speed GMAW on thin sheets

Productivity is one of the main drivers in manufacturing industries. For welded products, productivity is usually related to welding travel speed, but some welding defects related to bead shape, such as formation of bead humps and undercutting at the weld edges limit the maximum travel speed that can be industrially applied.
As a consequence, a better understanding of the humping phenomenon during the welding process is needed to lead to a significant breakthrough of welding speed increase. First a state of the art in the literature knowledge is presented, then our own experimental results are discussed and finally a way of improvement for GMAW is proposed.
A review of literature suggests that bead hump formation in GMAW is complex and probably involves more than one mechanism depending on process variables.
Through our experiments, we investigate the humping phenomenon with the observation of final weld geometry, microstructures, parametric study of welding conditions and parameters. We also dynamically captured the humping appearance using high speed video imaging. Our main conclusion is that the key event in humping phenomenon is the formation of a thin liquid channel generated by elongation of the molten metal deposit. Indeed this channel solidifies promptly and prevents backfilling of metal from the created hump.
In order to fight against this event we have first quantified the improvement of best practices known in the prior art. Then based on our theoretical study of the mechanism of the humping defect, we propose a new hybrid process based on GMAW and GTAW combination. A parametric study of this new process offered us the possibility of an increase of 30% of the welding speed.