Analysis and wavelet transform of vapor capillary dynamics during laser beam welding of aluminum gravity die-cast parts using in situ synchrotron diagnostics

In this study, laser beam welding (LBW) of gravity die-cast components made from the aluminum casting alloy EN AC-AlSi7Mg0.3 is investigated. The experiments are carried out using in situ X-ray observation with synchrotron radiation at the Deutsches Elektronen-Synchrotron (DESY), PETRA III beamline P07 EH4 in Hamburg, Germany. Phase-contrast videography is employed to investigate the keyhole dynamics in the LBW process, and the resulting weld pool ejections are visualized. In this investigation, the wavelet transform is introduced for time-resolved frequency analysis of keyhole dynamics in the welding process. First, the statistical fundamentals of the wavelet transform are presented based on the current state of the art. In preliminary studies, locally varying weldability is quantified using the position-dependent empirical probability of melt pool ejections. Melt pool ejections are classified as either stochastic or systematic. The subsequent wavelet analysis visualizes the frequency behavior of the maximum keyhole depth. This is followed by a position-dependent comparison of welds using frequency analyses based on the wavelet transform. This methodological study confirms the suitability of the wavelet transform for time-resolved frequency analysis of keyhole dynamics in LBW.