Numerical Simulation Of The Dynamic Behaviors Of Laser Heat-conduction Butt Brazing On Beryllium Plate

For the optimization of welding parameters used in laser heat-conduction (LHC) butt brazing of Beryllium plate, a 3-D transient numerical model is established for the fluid flow and heat transfer in LHC butt brazing to investigate the dynamic behaviors of weld pool.Basing on the features of centerlized energy density and small Depth-width ratio of weld pool in LHC butt brazing of Beryllium plate, a complex heat source model, an exponential rotary parabolic body heat source model and a linear rotary parabolic body heat source model are established respectively to describe heat transferred from laser beam into weld pool, and then their responding expressions are given. According to the energy conservation, momentum conservation and mass conservation, the governing differential equations are derived, and then their corresponding initial conditions and boundary conditions are listed. Moreover, the governing equations are discretized and calculating software in FORTRAN is programmed.The dynamic behaviors of weld pool are analyzed numerically by using the new heat source model and mathematical model. Firstly, the advantages and disadvantages of the three heat source models in the numerical simulation of heat transfer in LHC butt brazing of Beryllium plate are studied. The comparison between the predicted results and the measured one indicates that the exponential rotary parabolic body heat source model is the best one suitable to describe the heat input distribution. Second, a vertical material method for numerically treating the butt gap between solder and base metal in LHC butt brazing of Beryllium plate is developed. The vertical material in butt gap has specific themophysical parameters that are differ from those of both solder and base metal. The effects of thermophysical parameters of vertical material, such as thermal conductivity, density and specific heat, on predicted results are carefully analyzed and the optimum values of thermophysical parameters are determined. Finally, the dynamic behaviors of weld pool in different welding parameters such as laser power and welding speed are calculated. The transient developments of 3D heat field, fluid field and shape of weld pool in a condition of constant laser power and welding speed are obtained and the variation tendency of 3D heat field, fluid field and shape of weld pool in a condition of different laser power and welding speed are also analyzed.This study would provide basic data and theoretical instruction for the industry application and optimization of welding parameters of LHC butt brazing of Beryllium plate.