Investigation of Vapor Plume and Molten Pool in Pulsed and Continuous Keyhole Welding Based On a Three-Dimensional Dynamic Model

Laser keyhole welding is a complicated multi-phase, multi-physic process. A three-dimensional numerical model is developed to investigate the dynamics in laser keyhole welding in a self-consistent manner. The model accounts for the heat/mass transport phenomena as well as the transient change of keyhole shape, and special efforts have been spent to (a) treat the gaseous phases as compressible materials, (b) track the distribution of different chemical species in the keyhole plume, and (c) capture the steep changes of material state and physical properties across the sharp interface between liquid and vapor phases, i.e., the keyhole wall. The model is utilized to predict the keyhole evolution during its formation and collapse stages, the flow patterns in both the gaseous and liquid regions, and the effects of various phenomena are discussed, including plasma absorption, multiple-reflections, material evaporation and surface tension. Moreover, the effect of the assisting gas on the keyhole stability, through mechanical impact and chemical mixing, are also investigated.  The accuracy of the predictive model is shown via experimental validations.   The model is extended to investigate the different hydrodynamic patterns in the continuous welding process to reveal the details of laser keyhole welding mechanisms under various conditions.