An evolutionary keyhole-mode heat transfer model in continuous plasma arc welding

Abstract

Keyhole plasma arc welding is superior to other ordinary arc welding technologies in deep penetration welding. Energy can be transferred to bottom metal by hot plasma arc in keyhole rather than merely by heat conduction through whole thickness. Hence, an evolutionary keyhole-mode heat transfer model was developed to demonstrate this thermo-physical process. In view of the relative movement of plasma torch and workpiece, a double-elliptical heat source was set up on top surface and a developing conical heat source below, which is closely related to keyhole depth by Volume of Fluid method. Based on analogy to practical welding process, a dynamic energy distribution coefficient was established and an adjustment factor was introduced to account for pressure variation. According to numerical simulation, evolutionary energy propagation process, corresponding temperature field and molten pool geometry were demonstrated simultaneously. The dynamical keyholing process and the consequent keyhole-mode heat transfer and fluid flow were revealed in continuous keyhole plasma arc welding. Experiment was conducted on an 8 mm-thick stainless steel plate, and the measured weld geometry, keyhole size and keyhole exit deviation show reasonable agreement with calculated results.