A methodology to integrate melt pool convection with rapid solidification and undercooling kinetics in laser spot welding

摘要

In laser spot welding because of small melt pool and short process duration, the welding process takes place rapidly with high cooling rates. As a result the analysis of solidification in laser spot welding becomes challenging. The solidification takes place generally with non-equilibrium kinetics involving undercooling and recalescence. In this work, a methodology for handling the rapid solidification in laser spot welding is developed by solving the coupled transient conservation equations of mass, momentum and energy. Undercooling and recalescence are coupled with the melt pool convection and heat transfer using an interface tracking algorithm which predicts the rapidly evolving interface temperature and interface speed. The melt pool result is first validated with the published results. Thereafter, the effect of undercooling is investigated by presenting a detailed comparison of results obtained from the rapid (non-equilibrium) solidification model and the conventional (equilibrium) solidification model. The results conclude that undercooling and recalescence have profound effect on melt pool dimension, temperature, solidification time and melt pool convection. The rapid solidification behavior is delineated further with the help of solidification parameters, such as interface temperature, solidified thickness, temperature gradient (G) and solidification rate (R). The weld microstructure is estimated using the combined values of GR and G/R.