Sensitivity Analysis on Numerical Simulation of the Weld Pool Shape in Tig Welding

Gas tungsten arc welding (GTAW) is a technique widely used for joining steel in nuclear industry where the weld quality must be ensured. An increased productivity of welding would have a very important economic impact for the industrial sector, but the occurrence of some welding defects, such as humping and undercutting at the weld edges limit the welding speed. Although GTAW is already a very efficient process, it can be improved, especially with respect the welding speed.

Simulation is a very powerful tool to help in understanding the factors limiting the quality of welding. A 3D finite element model of heat and fluid flow in weld pool considering free surface of the pool and traveling speed has been developed for the GTAW process. Cast3M software is used to compute all the governing equations. The free surface of the weld pool is calculated by minimizing the total surface energy. The combination effects of surface tension gradient, buoyancy force, arc pressure, gravity to drive the fluid flow is included in our model. The deformation of the weld pool surface and the welding speed affect fluid flow, heat flow and thus temperature gradients and molten pool dimensions and the humping phenomenon which occurs at a high arc pressure and welding speed. To understand the effects of different factors such as arc pressure, welding speed and free surface a sensitivity analysis has been performed. Welding trials study is also presented to compare our numerical results with macrograph of the molten pool. Filler metal isn't considered in the presented model of the weld pool. However heat and material deposit will be shortly included in the model to improve the prediction of welding quality for the moving GTAW process with metal deposit.