TOWARDS A SELF-CONSISTENT MODEL OF THE KEYHOLE IN PENETRATION LASER-BEAM WELDING

The stability of a cylindrical keyhole is investigated using the energy and pressure balance. Non-equilibrium evaporation from the keyhole surface, surface tension, hydrostatic and hydrodynamic pressure in the melt as well as heat conduction into the workpiece are considered. In contrast to former investigations, the temperature at the keyhole wall and the radius of the keyhole adjust themselves self-consistently. A threshold for the laser power per thickness of the workpiece is found above which the formation of a stable keyhole commences. For iron, this threshold is 790 W mm-1. The temperature at the keyhole wall exceeds evaporation temperature by approximately 100 K The keyhole radius exceeds the radius of the laser beam and is at least 1.7 times the laser radius.