Laser Hemming Welding of Aluminum Alloy Sheets for Autobody Application 931935

This study was carried out to investigate the CO₂ laser weldability of aluminum alloy sheets for the welding of hemmed region. Efforts were made to obtain the best bead dimension for hemming welding. Thus, a following criterion was formulated: a hemming bead which has less than 0.8 mm of welding depth and more than 1.0 mm of welding width works satisfactorily for hemming joint in terms of both strength and visual appearance. The dimension of hemming bead was greatly affected by surface conditions as well as welding parameters. Clean surface condition coupled with helium shielding gas produced a most sound welding bead. The effect of lubricant on the formation of welding defect was also investigated. It was found that the welding defect, i.e., porosity in the weld zone, was caused by the lubricant at the surface and degraded the strength of weld joint. The laser welding did not soften both the heat affected zone (HAZ) and weld zone of aluminum alloy sheets in this study. The fracture, therefore, occurred at the stress concentration site, not at the HAZ.