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Product Code: ICA13_405

Complete Heat and Fluid Flow Modeling of Keyhole Formation and Collapse During Spot Laser Welding
Authors:
Mickael Courtois, Limatb - Ea 4250; Lorient France
Muriel Carin, Limatb - Ea 4250; Lorient France
Philippe Le Masson, Limatb - Ea 4250; Lorient France
Sadok Gaied, Arcelormittal; Montataire
Mikhael Balabane, Institute Galilee Universite; Villentaneuse France
Presented at ICALEO 2013

During laser welding of metals, an important issue is the understanding of phenomena responsible for defects in the solidified welded joint. With the increasing of computation capabilities, models developed in recent years become more physic and need less and less restrictive assumptions. Nevertheless, some efforts remain to be done to offer robust and predictive models to explain key phenomena. The vapor plume, its interaction with the melt pool and its role are not yet totally mastered. In this instance, a model is developed in order to offer an adaptive tool, the more predictive as possible in the commercial code Comsol Multiphysics®. The model takes into account the three phase, namely: the vaporized metal in the keyhole with the plume generation, the liquid metal in the melt pool and the solid metal base. The coupled energy and momentum equations are solved in the three phases. The free surface of the keyhole is tracked with the fixed mesh method Level-Set. The phase change during vaporization is treated with an original approach, which introduces a source term in the continuity equation to represent the vapor generation and the resulting recoil pressure. The mass flow rate is deduced from the temperature and the recoil pressure is modeled by momentum equations without introducing volume forces (Knight‘s formulation). To model the energy deposition, in contrast of the complex ray tracing method, a new approach is proposed which consists of treating laser under its wave form by solving Maxwell’s equations. This new approach coupled with the Level-Set method is fully implementable in commercial software. The presence of mask at the surface or the effect of polarization can easily be simulated. This paper presents this new approach and its validation. The results obtained with the complete model of heat and fluid flow are analyzed in a 2D axially-symmetric configuration. The mechanism of porosity capturing during the collapsing of keyhole is described. Finally, the model is compared with experimental results in terms of melt pool dimensions and its dynamic evolution.

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