Thermal-Fluid Model for Weld Pool Geometry Dynamics

Abstract

This paper describes an experimental and analytical program to provide a predictive weld pool modeling technique useful as one component of a feed back control automatic welding machine. Stationary arc experiments were performed with stainless-steel plugs and showed two different regimes in the growth of the weld pool. Initially the surface tension driven flow was dominant in the shaping of the pool (t<3 s). Once enough material was molten, the electromagnetic (E-M) forces became the dominant factor. This behavior was also observed for the moving arc cases. Detailed measurements of the pool shape were made for steady and transient conditions. A thermal-fluid model of the weld pool was developed for the case of a stationary arc in which a deep paraboloidal pool is formed. This model uses the current and heat distribution at the anode surface as inputs. Matching of convective and conductive heat fluxes along the melt boundary was used to predict the weld pool shape. The conductive heat flux on the solid side was calculated by the finite element method. The convective heat flux on the liquid side was calculated by solving the fluid and heat transfer equations assuming a single cell circulation flow inside the weld pool. For the stationary arc cases under consideration, the E-M force field was found to dominate the flow pattern. This method was capable of determining the transient in weld pool geometry for changes in different process conditions, e.g., arc length, pulsed current. Comparison between experiments and the model showed agreement of weld pool size (top width and penetration) within 10 percent. This modeling technique can be extended to analyse weld pools with multi-cell circulation patterns which are encountered in the moving arc and the stationary arc cases with a shallow pool.