Abstract
The flow-field of a molten pool of the laser welding was simulated by solving the 3-dimensional Navier-Stokes equation. The keyhole diameter and depth were assumed to be 1mm and 6mm for the 4.8kW CO2 laser welding condition. The body force of (10)^7N/m3 by the evaporation reaction was given at the keyhole front region. The temperature gradient of the surface tension was assumed to be -0.5mN/mK. and the Marangoni effect was considered. The descending flow was formed at the front of the keyhole, and its velocity was about from 0.2m/s to 0.5m/s. It is enough for the bubble of 0.3mm∿1mm diameter of to be separated from the keyhole by the fluid force against the surface tension and the buoyancy. Some of the bubbles were trapped in the solidification region, which remained as the porosity.
