Influence of the brazing speed on the seam characteristics in laser beam brazing of zinc coated steel

In car body manufacturing, the joints in the outer skin exterior shell are especially challenging. They have to fulfill very high surface quality requirements. Laser beam brazing of electrogalvanized steel is a well established process for these joints in the direct view of the customer. However, the quality of the brazed seam is very sensitive to changes in the process parameters or in the environmental conditions. Currently, the process speed is limited due to quality requirements of the brazed seam. In this paper, the authors describe the influence of the brazing speed on the resulting braze seam. By the use of high-speed videography, the authors study the process and analyze the occurring macroscopic effects. The two main effects that can be observed with high-speed videography are surface instabilities and an inhomogeneous movement of the melt pool front. Moreover, the authors could detect a correlation between the movement of the melt pool front and the formation of notches.