Computerized simulation of laser beam weld formation comprising joint gaps

A model of laser beam weld shape formation which comprises butt and overlap joints with a small gap between the parts to be joined is considered. It is the goal of the simulation to predict the effect of technological parameters on the reinforcement or concavity of the weld or weld root and on the area of the load-carrying cross section which controls the strength of the joint. The model is based on the equations of energy transport and of equilibrium at the free surfaces for balancing vapour pressure, capillary pressure and a correction term. The correction term allows balancing the metal volume taking into account thermal expansion and shrinkage during welding and the gap width between the parts to be joined. Verification of the simulation results for gap widths in the range 0-0.2 mm shows that the model corresponds sufficiently well to the experimental data when considering laser beam weld formation in butt and overlap joints of 1.5-6.0 mm sheet thickness. The model explains the weld concavity occurring with gaps in butt and overlap joints, the increase in penetration depth for butt welds with gaps and the widening of the molten zone near the gap in overlap joints.