Stochastic model of the deep penetration laser welding of metals

Abstract

Deep penetration laser welding of metals generates a keyhole surrounded by a molten region which forms the weld on freezing. Mathematical models of the process produce relationships between the process parameters to provide an effective simulation of the process and a guide to optimal operating conditions both for continuous wave (cw) and pulsed systems. It is usual when pursuing such an analysis to assume the existence of a suitably averaged keyhole structure. To assume a steady-state keyhole with suitably averaged properties, however, constitutes a considerable idealization. Actually, the keyhole manifests itself as a writhing, twisting entity. This characteristic arises from many different instabilities that can and do inevitably come into play. They represent the reaction of the material being welded to the laser beam. It is even more necessary to consider such reactions to the laser beam when pulsed lasers or cw lasers with pulsed modulation are considered. The details concerning the characteristics of specific instabilities are not considered here. Instead, a stochastic description of some aspects of the laser welding process is provided when the laser operates in the cw case. The applicability of current mathematical models is thus extended giving increased insight into the nature of the laser welding process.