Effect of shielding conditions of local dry cavity on weld quality in underwater Nd:YAG laser welding

During underwater laser beam welding (LBW), the welding quality is severely influenced by the shielding condition of the local dry cavity. In this paper, the stability of the local dry cavity and the effect of shielding condition on the weld quality during laser welding of Type 304 stainless steel were investigated. Firstly, welding experiments under various water depths without any way to exclude water from the welding zone were performed. It was found that one kind of laser-induced plasma having strong shielding effect to the incident laser beam forms when the laser irradiates the water directly if the water depth is larger than 3 mm. This shielding effect will lead to the impossibility of deep penetration welding in water. So in the welding, a water curtain nozzle was used to form a local dry cavity. The effect of the shielding conditions, e.g. water flow rate, gas flow rate and water flow angle, on the stability of the local dry cavity was studied. The welding results under various shielding conditions show the relationship between the shielding condition and the quality of the weld bead.