Simulation And Experimental Study On Flow Field Of Laser Welding Coaxial Nozzle

Laser deep penetration welding has high power density,and the plasma/feathers generated directly above the weld pool during welding will have an adverse effect on the absorption or scattering of incident laser light.The working gas is usual y output through the welding nozzle to regulate the plasma/feathers,and the welding pool is protected to ensure the stable implementation of the welding process.In the process of laser welding of precision components,the stability of weld formation and welding processes is particularly important.Therefore,in this paper,the coaxial welding nozzles are designed for CO₂ lasers and fiber lasers in combination with simulation calculations,schlieren experiments,and process tests,respectively,and their respective intracavity/out-cavity output gas flow states and the formation of weld seams are determined.The influence laws were studied,and the optimized nozzle structure and gas input parameters were obtained,which effectively controlled the weld forming quality.Firstly,for the coaxial welding nozzle,the fluent software was used to simulate the gas flow state under different structural conditions of the coaxial nozzle.It was found that each structure of the coaxial nozzle?gas input channel,collection zone,and output segment?was in the cavity/cavity.External output flow has a significant effect.Combined with the schlieren test,the output gas flow pattern of the coaxial nozzle was observed.It was found that the coaxial nozzle with the optimized structure can simultaneously realize the laminar output and reverse output of the gas,and achieve the dual effects of protecting the molten pool and preventing air entrainment above the nozzle.Through the implementation of CO₂ laser welding test,combined with the weld morphology analysis,analysis of the optimization structure of the coaxial nozzle in the CO₂ laser long welding seam welding stability.Through experimental research,the structure of double-layer coaxial welding nozzle was proposed for the feather plume eruption characteristics of fiber laser deep penetration welding.Through the simulation calculation of the external nozzle gas flow state,the flow characteristics of the outer nozzle output working gas flowing along the outer nozzle wall of the inner layer are obtained.Through the schlieren test,it was observed that the gas flow states of the inner and outer nozzles can influence each other.Then systematically studied the influence of working gas flow,atmosphere and welding process parameters on welding quality.Through the welding process test and the detection of weld profile and composition,the optimized input gas parameters and structural characteristics of the double coaxial welding nozzle were obtained.On this basis,a fiber laser coaxial working head was designed and tested.The results show that the local atmosphere above the molten pool in fiber laser welding has a significant regulatory effect on the welding process stability,weld formation and spattering behavior.