Method to Reduce Calculation Time in Multiphysics Modelling of Welding Processes. Application to Laser and GMAW Welding
The heat and fluid flow calculation inside the melt pool in welding processes is a complex challenge. It can be useful to predict defects in the weld seam or to study the influence of some process parameters. Even if the required equations are mastered over the last few years, the cost in time of these calculations and the complex topology of the free surface make these models difficult to introduce in an industrial study.
The aim of this presentation is to propose a complete model solving the heat and fluid flow equations in all the states (solid – liquid - gas) of the metal during keyhole laser welding with COMSOL Multiphysics®. In order to track dynamically the keyhole shape, a level set function is employed and the momentum equations are solved to predict accurately the melt pool behavior.
The particularity of this model is a drastic optimization to reduce computation time (less than 1 day on a commercial workstation [6 cores @3,33 Ghz – 8 Gb RAM]) without reducing significantly the accuracy of the fluid flow computation. To achieve this goal, a simplified approach of the recoil pressure effect is employed and an original method with three different meshes adapted for each equation and each physics is proposed and discussed. A step of solution projection with identity operators is then needed. This optimization of each mesh for the special need of each equation reduces significantly the number of degrees of freedom, a key parameter to reduce calculation times.
To validate the model simplification, an experimental validation is added with longitudinal and transverse micrographic cuts for different welding configurations, micro-thermocouples measurements in solid phase [20 - 1300 °C], pyrometer measurements in liquid phase [1500 - 3000 °C].
In addition, the same method is employed to model in 3D the Gas Metal Arc Welding (GMAW) with the heat, fluid flow and electromagnetism equations to calculate arc and plasma phenomena. The droplet creation at the wire tip, its detachment and impingement in the melt pool are dynamically predicted with the level set method in only few days.
