Laser Spot Welding: Computer Model Validation Using High-Speed, High-Magnification Video Measurements of Solidification Velocities

Laser spot welding is a common technique for joining small components that require precise fit-up and small distortion after joining. Finite element models of the laser spot welding process are being developed so that more effective welds can be made. The models being developed use an arbitrary Lagrangian / Eulerian finite element method to predict the formation of the keyhole and the solidification velocities in the laser spot weld. These velocity predictions evolve from the recoil pressure caused by rapid evaporation from the high temperature molten surface and the thermal boundary conditions. The recoil pressure is used as a boundary condition to determine the deformation of the free surface of the molten pool. High-speed, high-magnification video microscopy experiments have been used to measure solidification velocities in actual laser spot welds. The welding modes filmed in this study are limited to welds with no keyhole formation. Solidification velocity data were extracted from video clips using computerized image analysis software. This data were compared to computer model predictions of solidification velocity. This comparison allowed for validation of the fluid and thermal boundary conditions used in the finite element model. Visualization and data extraction techniques will be discussed. Experimental data and predicted solidification velocities will be compared and discussed.