Experimental study of the dynamical coupling between the induced vapour plume and the melt pool for Nd-Yag CW laser welding

We discuss the effects of the interaction between the vapour generated by the ablation process occurring on the front keyhole wall (KW) during deep penetration Nd-Yag laser welding and the surrounding metallic melt pool. It is shown that the inclination of the front KW determines the importance of this process. At low welding velocities, the front KW inclination is small and therefore the drag forces induced by the expanding vapour accelerates a liquid thin film around the keyhole and parallel to its axis. At high welding velocities, the front KW inclination becomes large, and the evaporation process is very important. Therefore the expanding metallic vapour impinges on the rear KW and opens the keyhole aperture. These effects localize the droplet generation process. By using an adequate side gas jet nozzle, we show that we can stabilize the melt pool fluctuations, and therefore suppress droplet generation and improve the weld seam quality.