Frequency-based analysis of weld pool dynamics and keyhole oscillations at laser beam welding of galvanized steel sheets

The movements of the keyhole and the weld pool at deep penetration solid-state laser welding can be analyzed by observing either the optical process emissions, or directly the work piece surface using camera systems in the visual range. In this paper, the welding process of zinc-coated steel sheets is monitored. The geometry and behaviour of weld pool and capillary are calculated from the acquired camera images, they are compared with the onedimensional optical process emissions, and analyzed in the time- and frequency-domain. This helps to better understand the uncontrolled process behaviour, especially regarding the destructive influence of the evaporating zinc-layer.