Analysis of multi-phase interaction and its effects on keyhole dynamics with a multi-physics numerical model

A numerical model is developed to investigate the three-dimensional transient dynamics of the keyhole in continuous welding processes with/without assisting gas. The model features the utilization of the sharp interface method for accurate consideration of the complex boundary conditions on the keyhole wall and a comprehensive hydrodynamic calculation for both the gaseous and liquid phases. The model gives good prediction of the weld geometry, and more importantly, provides detailed information regarding the multi-phase interaction and its effects on keyhole dynamics. It is shown that different welding parameters can cause different coupling effects between the vapour plume and molten pool and hence produce keyholes of different shapes. The addition of assisting gas flow not only modifies the interaction between the vapour plume and molten pool, but also reduces the laser attenuation by the plume. These two-folded effects can significantly change the keyhole shape. The dependence of laser absorptivity on incidence angle is found to be a major source of keyhole fluctuation. If the welding heat input is high and the keyhole is deep, vertical and slim, the fluctuation may cause keyhole collapse and hence porosity in the final weldment.