Numerical modelling of shielding gas flow and heat transfer in laser welding process

In the present work a three-dimensional model has been developed to study shielding gas flow and heat transfer in a laser welding process using computational fluid dynamics. This investigation was motivated by problems met while using an optical system to track the weld path. The aim of this study was to investigate if the shielding gas flow could disturb the observation area of the optical system. The model combines heat conduction in the solid work piece and thermal flow in the fluid region occupied by the shielding gas. These two regions are coupled through their energy equations so as to allow heat transfer between solid and fluid region. Laser heating was modelled by imposing a volumetric heat source, moving along the welding path. The model was implemented in the open source software OpenFOAM and applied to argon shielding gas and titanium alloy Ti6Al4V base metal. Test cases were done to investigate the shielding gas flow produced by two components: a pipe allowing shielding the melt, and a plate allowing shielding the weld while it cools down. The simulation results confirmed that these two components do provide an efficient shielding. They also showed that a significant amount of shielding gas flows towards the observation area of the optical system intended to track the weld path. This is not desired since it could transport smoke that would disturb the optical signal. The design of the shielding system thus needs to be modified.