Process-limiting Factors and Characteristics of Laser-based Micro Welding

In this study the process of laser-based micro welding was examined using the example of ultra-thin stainless steel foils with total welding depths of 50 μm and 100 μm. For this purpose, focal diameters between 20 μm and 200 μm were applied to the work piece using scanning units with various image scales as well as a single-mode and a multi-mode laser with different fiber core diameters. In order to generate full penetration welds, the process windows were determined applying a power level up to 500 W as well as feeding rates up to 6 m/s. A relational expression concerning related power was defined in order to characterize and predict the lower process boundary. By means of high speed recordings the dependencies of process boundaries with respect to melt pool behavior have been clarified. Furthermore a changeover of welding regime within the process window was revealed and described dependent on the focal diameter.