Stabilization of laser welding processes by means of beam oscillation

Welding with high-brightness laser beams suffers from increased sensitivity of both, the process itself and the laser beam shaping optics[1]. Laser beam oscillations create comparably large melt pool surfaces while maintaining the high laser beam brightness. Fast laser beam oscillation is known to be favourable for joining of dissimilar materials[2][3]. In our work we use such oscillations to stabilize high-quality laser welding processes. Comparison of the cross sections for different oscillation properties clearly showed that the welding depth is determined by the static beam properties, i.e. high brightness, while the weld width is given by the oscillation amplitude. The width corresponds to the width which is obtained by a static, lower brightness beam that has parameters equal to the time averaged oscillating high-brightness beam. We denote the time averaged oscillating beam as "virtual lower quality beam". It follows that in many cases the process efficiency given by the amount of melt is improved by oscillation since we combine the welding depth - and hence increased coupling efficiency - achieved with the high-brightness beam with the width of the time-averaged oscillation High-speed videos show that motion patterns have to be chosen carefully in order to minimize unwanted effects such as e. g. melt ejection. However, the aim of the present investigations is to improve process stability, in particular to make the welding process less sensitive to focal shift. Therefore the results of welding with an oscillating laser beam in different focus positions are discussed with respect to process stabilization.