Study of Nd-YAG laser welding of Zn-coated steel thin sheets Available to Purchase

The welding of Zn-coated steel thin sheets is of very great importance for the automotive industry. Previous studies have shown the main involved physical processes. The zinc vapor coming out from the interface of the two sheets is violently expelled inside the keyhole and expels the melt pool, for non controlled conditions. When using CO2 lasers, we have previously shown that an elongated laser spot produces an elongated keyhole, which is efficient for suppressing this effect. We recently adopted a similar approach for Nd:Yag laser welding. We observed that an elongated spot was not necessary for achieving good weld seams. Several diagnostics were used in order to understand these interesting results. High speed video camera visualizations of the top and the bottom of the keyhole during process show the dynamics of the keyhole hydrodynamic behavior. It appears that the role of the reflected beam on the front keyhole wall is crucial for an efficient stabilization of the process. Our dynamic keyhole modeling, that includes ray tracing, totally confirms this interpretation and explains the results for very different experimental conditions (effect of welding speed, laser intensity, variable sheet thickness, laser beam intensity distribution) that will be presented.