X-ray analysis of capillary and melt pool dynamics using laser beam oscillation welding for aluminum die-casts

The knowledge of underlying physical phenomena and the understanding of parameter dependencies are essential for the development of stable welding processes. Quantitative data based on a sensor-based approach are necessary to draw conclusions about the resulting quality. These are at the same time key factors for the optimization of industrial processes. The paper refers to this in the context of laser welding technology using superimposed dynamic beam oscillation of aluminum alloys. However, particularly die-cast aluminum is characterized by limited weldability due to entrapped gases, which lead to defects like high porosity and blow out formation along the weld seam. For the welding trails, a novel laser processing head was designed. The optics enables a synchronized and fast beam deflection in all three spatial directions. Therefore, a galvanometer scanner for x-y-oscillation was combined with a piezo-driven mirror for the beam movement in the z-direction. By means of in situ synchrotron x-ray imaging synchronized with recordings of acoustic process emissions and high-speed imaging of the melt pool, deep insights into the interactions of the laser beam and material could be investigated. The collected data show a clear correlation between oscillation parameters (frequency and amplitude) and the resulting weld seam quality. Furthermore, audio signal information provides an explicit link for different vapor capillary formations as well as melt flow fluctuations. The adapted process dynamics for dynamic beam oscillation welding enable a significant quality improvement and open up the possibility for efficient and safe process monitoring.