Abstract: Aiming at the problem of easy oxidation in welding of chemically active metals such as titanium alloy, which leads to serious deterioration of welding quality. Taking the protective device of titanium alloy laser welding as the research object, to obtain a good welding protective effect, a kind of double coaxial laser welding protection nozzle is designed. The flow field simulation software Fluent is used to simulate and optimize the parameters of the double-layer coaxial protection nozzle, including the inner and outer layer wall structure, the number of the outer protection nozzle inlet, the inlet Angle, whether there is spiral structure at the outlet and the flow rate of the protection nozzle. The final protection nozzle structure is obtained by comparing the protection effect of the airflow in the protection area. The optimized protective nozzle is fabricated by additive manufacturing technology. The titanium alloy laser welding experiment is carried out on the designed laser welding protective nozzle by changing the flow rate of the protective gas of the inner and outer nozzle, and the protection condition is compared with that of the side-axis nozzle. The results show that for the protective nozzle with an arc shaped inner and outer wall structure, four 45° air inlets, and a 30° spiral structure at the outlet, the protection range is limited when protective gas is only applied to the inner nozzle, and the weld color is dark yellow, resulting in severe oxidation pollution. As the flow rate of the outer protective gas continues to increase, the weld color changes to yellow, silver white, and blue. The welding protection effect is best when the flow rates of the inner and outer protective gases are respectively 10 L/min and 20 L/min. And the protection effect is not affected by changes in welding direction, which can create a good gas protection environment for the workpiece.

Key words: laser welding, double coaxial protection nozzle, Fluent, additive manufacturing