Experimental determination of influencing factors on the humping phenomenon during laser micro welding of thin metal sheets

Industrial applications such as joining pressure sensors or battery cells often demand short processing times for economic reasons. Thin metal sheets of thickness smaller than 100 mu m are suitable for this purpose. The possible maximum feed rate for an efficient welding process is limited by weld defects, which occur at a certain threshold value of feed rate. Materials such as stainless steel, aluminum, and titanium were welded in bead-on-plate welds in order to generate a full penetration weld. Here, our attention is focused on understanding this instability. In this paper, we performed tests to clarify the influence of the thermophysical properties of the applied materials and the process factors laser power and focal diameter on the humping effect. Due to these attributes, the weld seam formation and hydrodynamic behavior of the melt change. By means of microscopical surface line scans and high-speed imaging, the observations were analyzed depending on the feed rate. The results from the line scans provide the possibility to analyze the surface topography of the weld seam. In particular, the distance, height, and axial frequency of the solidified humps can be categorized in order to get a deeper understanding of the solidified hump structure and the phenomenon in general. To avoid the occurrence of humping, a criterion is defined by the ratio of laser power to weld seam cross section for the applied materials. (C) 2017 Laser Institute of America.