An investigation on the effects of side assisting gas flow and metallic vapour jet on the stability of keyhole and molten pool during laser full-penetration welding

This paper reports on a study aiming at separating the effects of side assisting gas flow from a metallic vapour jet on the transient behaviour of a molten pool and a keyhole during laser full-penetration welding. To achieve the research purpose, laser welding process was simulated under three different conditions: in the presence of both side gas flow and metallic vapour jet, in the presence of side gas flow alone and in the presence of metallic vapour jet alone. It was found that the side gas flow not only pushed the molten melt to flow towards the rear part of the molten pool but also formed, on the molten pool surface, a proper pressure distribution which helped maintain both the humping in the rear part of the molten pool and the concave around the upper exit of the keyhole. Under the condition with side gas flow, the swelling formed around the keyhole blocked the side gas flow and on the other hand the side gas flow pushed them to flow backwards to the rear part of the molten pool more effectively, thereby enlarging and stabilizing the keyhole exit. Furthermore, the peak value of the average pressure in the region composed of the molten pool and keyhole decreased step by step with the growth of the concave. Finally, the interaction between the metallic vapour and molten melt was well controlled using the side gas flow, which led to an improvement in the stability of the molten pool and a reduction in spatters and pores.