Modelling of Electric Arc Welding: arc-electrode coupling

Licentiate thesis, 2013

Arc welding still requires deeper process understanding and more accurate prediction of the heat transferred to the base metal. This can be provided by CFD modelling. Most works done to model arc discharge using CFD consider the arc core alone. Arc core simulation requires applying extrapolated experimental data as boundary conditions on the electrodes. This limits the applicability. To become independent of experimental input the electrodes need to be included in the arc model. The most critical part is then the interface layer between the electrodes and the arc core. This interface is complex and non-uniform, with specific physical phenomena. The present work reviews the concepts of plasma and arc discharges that are useful for this problem. The main sub-regions of the model are described, and their dominant physical roles are discussed. The coupled arc-electrode model is developed in different steps. First coupling solid and fluid regions for a simpler problem without complex coupling interface. This is applied to a laser welding problem using the CFD software OpenFOAM. The second step is the modelling of the interface layer between cathode and arc, or cathode layer. Different modelling approaches available in the literature are studied to determine their advantages and drawbacks. One of them developed by Cayla is used and further improved so as to satisfy the basic principles of charge and energy conservation in the different regions of the cathode layer. A numerical procedure is presented. The model, implemented in MATLAB, is tested for different arc core and cathode conditions. The main characteristics calculated with the interface layer model are in good agreement with the reference literature. The future step will be the implementation of the interface layer model in OpenFOAM.