Numerical Simulation Of Thermal Process And Fluid Flow In Laser-MIG Hybrid Weld Pool

Laser-MIG hybrid welding is a welding process with high efficiency and weld quality.Heat and mass transport action and fluid dynamics behavior of weld pool have a decisive influence on hybrid welding process and weld quality.Therefore,it is of great significance to study the thermal process,fluid flow and keyhole dynamics by using the method of numerical simulation.In this way.the mechanism of Laser-MIG hybrid welding process is revealed,and the welding parameters are optimized.In this study,Laser-MIG hybrid welding processes with two configurations are considered.One is laser leading/MIG arc trailing,and the other is arc leading/laser trailing.For accurate description of energy deposition within the keyhole,the Fresnel absorption and the multiple reflections absorption are taken into account to describe the laser heat distribution.The metal transfer is treated as a periodic molten metal flow with specific temperature and velocity,and the effect of inclined torch on the droplet transfer is considered.The Continuum Surface Force method is employed to deal with the conversion of heat and force of the welding process from surface distributions to volumetric distributions.In the calculation,the thermal physical parameters of materials such as thermal conductivity and specific heat are temperature dependent.The grids are meshed by Gambit software,and numerical calculation is done by ANSYS FLUENT software,where the VOF method and PISO algorithm are used.The Laser-MIG welding processes on 6.6 mm thickness high strength steel and 8 mm thickness high nitrogen steel plates are numerically simulated,respectively,for the laser trailing configuration.The formation,growth and dynamic variation of keyhole are analysed.Meantime,the molten pool temperature field and fluid flow are quantitatively investigated according to their distributions on the longitudinal section,cross section and top surface.The corresponding laser-MIG hybrid welding experiments are carried out to verify the numerical models.The simulation results of Laser-MIG hybrid welding in laser leading/trailing configuration are compared to investigate the effect of the relative location of laser and MIG arc on the temperature field and fluid flow in weld pool.For the laser trailing configuration,the front wall of keyhole is easy to become unstable because of the impact by arc pressure and droplets,and the back wall of keyhole is mainly affected by the backward flow at the rear part of weld pool.For the laser leading case,the front wall of keyhole has good stability,and he arc pressure and droplets impact on the back wall of keyhole,which results in embossments or even closure of the keyhole.