The influence of the ratio between the wire and process velocities on the wetting process during laser brazing

Abstract

Laser brazing is used in automotive production for the joining of car body parts with customer-visible seams, whereby the highest optical seam quality is demanded. During the wetting process, a constriction formation can occur within the molten brazing material, which subsequently collapses; this induces a stepwise progression of the wetting front, thereby decreasing the optical seam quality. The aim of this study is to investigate the influence of the wire and process velocities on this constriction formation. For this purpose, high-speed recordings of the process zone are performed during laser brazing and then evaluated concerning the wetting process. The results show that the constriction formation depends on the relationship between the process velocity and the process direction component of the wire velocity. The constriction formation only occurs when the process velocity exceeds the parallel-oriented component of the wire velocity. This constriction formation is unstable and collapses repeatedly. In this study, increasing velocity differences stabilizes the constriction existence. This stabilization correlates with a uniform wetting process and a reduced frequency of the occurrence of blowout events, probably due to improved outgassing of zinc bubbles from the melt pool.