A Numerical and Experimental Investigation of Heat and Fluid Flow in Electric Arc Weld Pools

摘要

A numerical and experimental study of the influence of convection on temperature distribution and weld pool geometry during gas tungsten arc (GTA) welding of low alloy S460M-steel has been carried out. A comprehensive model of thermofluids phenomena has been implemented on the basis of commercial CFD-code FIDAP~(TM) The model considers thermo-capillary and electromagnetic forces, buoyancy, volume expansion, arc pressure and heat exchange mechanisms, including heat input by the arc and heat losses due to evaporation, radiation and convection. Special emphasis was put to the free surface phenomena. The free surface position of the weld pool is considered as an additional variable to be solved. The surface configuration is computed from the equilibrium between the hydrodynamic, hydrostatic and arc pressure from one side and capillary forces from the other, under influence of the thermal and phase-change volume expansion. The above extensions over other known weld pool models allow more exact calculations to be carried out. The numerical results have been thoroughly compared with the experimental stationary GTA welds of the material studied. The stationary weld pools were produced on the plates placed over a calorimetric cell. Both, the weld pool geometry and the heat flux across the plates have been used for the model verification. Qualitatively different weld pool shapes were obtained using argon and helium as shielding gases. When we/ding with argon, groove is formed at the weld pool periphery, resulting in an increase of the weld pool depth with increasing the distance from the centre. The helium arc results in a much deeper penetration, which is attributed to the action of electromagnetic body forces. With a proper choice of the model parameters an agreement between calculations and experiments can be obtained. However, in order to make reliable numerical predictions in general cases, more exact models of heat and current fluxes from the arc to the workpiece have to be considered. Also mechanisms responsible for the surface tension, evaporation phenomenon and the possible role of turbulence need to be deeper investigated.