The three-dimensional modeling of the plasma arc and metal transfer in arc welding

Most previous three-dimensional modeling work on arc welding focused on the weld pool dynamics. Almost all these weld pool models were based on the two-dimensional axisymmetric Gaussian assumptions of arc pressure, plasma heat flux, and/or current density. They may not represent the real situation when the metal droplet presents. Furthermore, the real world is three-dimensional and the non-axisymmetric plasma arc caused by the moving arc, joint configurations, and external perturbations can not be handled by a two-dimensional plasma arc model. This dissertation presented a newly developed three-dimensional model for the plasma arc. It is more computationally efficient as compared with an existing model. The mathematic formulation includes both Navier-Stokes equations and Maxwell's equations. Through solving these governing equations, it is possible to predict the velocity, pressure, temperature, electric potential, current density, and magnetic field of the plasma arc. The correctness of the model was verified by comparing the numerical results to the experimental measurements in GTAW. They were in good overall agreements. The developed model was also applied to the GMAW case. By integrating it with the simplified droplet transfer model in GMAW, the evolvement of the plasma arc under the influence of droplet transfer was studied. The numerical results showed that the distributions of arc pressure, plasma heat flux, and current density on the workpiece surface were time-dependent, not time-invariant as used in the previous weld pool models. It was found that these distributions were nonaxisymmetric for a moving arc.