Computer Modeling of Keyhole Mode Laser Welding To Avoid Maencecro-porosity

A transport phenomena based numerical model is developed to predict the keyhole geometry and temperature profiles in the weldment during laser welding. The model can be used to prevent macro porosity formation during laser welding of automotive aluminum alloys. The experimental results show that the weld metal contains large pores when the welding mode changes from conduction to keyhole mode or vice versa due to changes in welding variables. Based on this observation, the mathematical model predicts macro porosity formation when welding is conducted under conditions where small changes in welding parameters lead to a change in the welding mode. The model has been used to predict the geometry of the keyhole and the fusion zone, and the weldment temperature field for laser welding of aluminum alloys 5182 and 5754. The calculated weld pool depth, width, and shape for different welding speeds agreed well with the experimental results. The results showed that the keyhole profiles for high speed welding were asymmetric. Negative beam defocusing resulted in deeper keyhole than that obtained with positive beam defocusing. The transition from keyhole to conduction mode was more abrupt for negative beam defocusing. The model could predict formation of macro porosity during laser welding of aluminum alloys 5182 and 5754.