Simulation of vapour keyhole and weld pool dynamics during laser beam welding

摘要

To help get a deeper insight into highly-complex characteristics of laser beam welding, a mathematical model, closely mapping all prominent phenomena, is useful. Some phenomena such as surface tension induced forces, recoil back pressure, multiple reflections of laser rays and angle dependent energy absorption of hot surfaces are all crucial. Encompassing all those presences, a simulation model has thereby been developed. A laser power transmission model built in conformity with the ray tracing scheme is proposed along with a consistently-adaptive system of time stepping and meshing. The simulation results demonstrate a tailing, deepening weld pool wrapping around an unsettled vapour keyhole forming and collapsing in a fickle manner. Besides, the development pattern of the total laser power literally conveyed to the workpiece seems well matching with the prevalent understanding on broad deep-penetration welding processes. Experimental verification comes in the end. The simulated weld pool shape at its presumably-mature state is compared with that from the laboratory. A continuous-wave multimode Ytterbium-doped fibre laser was employed in the experiment to weld a plain 6-mm-thick stainless steel plate. Apart from the computed weld pool depth appearing somewhat deeper than it is supposed to be, the calculated weld pool width and length are in good agreement with the measured ones.