Study of the influence of the electrode tilt angle in GTAW doing CFD simulation of the heat source

Övrigt, 2013

Gas Tungsten Arc Welding (GTAW) is often used in production tilting the electrode by a few degrees. However, when GTAW is studied using Computational Fluid Dynamics (CFD) the electrode uses to be assumed perpendicular to the base metal (i.e. zero tilt). This bachelor thesis aimed at investigating if a perpendicular electrode is a valid approximation for the CFD simulation of GTAW process with 12° electrode tilt. No earlier simulation study with a similar aim is known. The project started from a simplified problem with electromagnetism (and no fluid flow) in an infinite electrically conducting rod. This problem has a known analytical solution that was used for validating the simulation results. A 3D mesh was developed for this test case so as to reproduce the analytic solution with good accuracy. This mesh was then used as base for building the 3D mesh of the GTAW problem. The model describing the physics of GTAW combines the electromagnetic model with a thermal fluid model. The 3D mesh was reduced to half space because of symmetry along the welding path. After memory related problems the number of cells of the mesh had to be further reduced. Two test cases that only differ by the electrode tip angle (0° and 12° angle) were simulated. The simulation results show that on the top surface of the base metal the shape of the heat affected zone is narrower behind the electrode and wider in front of the electrode for a 12° tilt compared to a 0° tilt. The heat distribution on the base metal is thus influenced if the tilt angle is 12°. This shows that a perpendicular electrode is not a valid approximation for the CFD simulation of GTAW process with a 12° electrode tilt.