Self-consistent modeling of keyhole and weld pool dynamics in tandem dual beam laser welding of aluminum alloy

A three dimensional model incorporating heat transfer, fluid flow and the keyhole free surface, Marangoni force, surface tension and recoil pressure is described. Possible multiple reflection Fresnel absorptions in complex keyhole profiles and laser plume interactions are also treated in the model. The results show that the keyhole is usually highly unstable and its depth undergoes severe oscillations in deep penetration tandem dual beam laser welding. The frequency of the depth oscillations is several kHz, which is comparable to that in single beam laser welding. Under the same heat input conditions, the amplitude of keyhole depth oscillations is smaller than that in single beam laser welding. Increasing the welding speed could improve the keyhole instability in dual beam laser welding. The mechanism of process stabilization of tandem dual beam laser welding over single beam laser welding is a joint effect of several beneficial physical factors, but not only the common known degassing effect. Good agreement is obtained between simulation results and prior experiments. (C) 2014 Elsevier B.V. All rights reserved.