Plasma arc and weld pool coupled modeling of transport phenomena in keyhole welding

Plasma arc welding involves intricate thermal, electrical, magnetic and fluid dynamics phenomena. To date, tremendous research has been carried out on the weld pool or the thermal plasma arc separately. Yet few studies have integrated the both aspects, much less the keyhole effect in addition. Accordingly, as an endeavor to advance the understanding of the transport phenomena in keyhole welding with plasma arc, a unified model coupling plasma arc and weld pool has been developed to help gain access to the more complete knowledge of energy conversion in the thermal plasma process and heat transfer to the weld pool with the consideration of keyhole effect. By solving a series of governing equations that contain the mass, the momentum and the combined thermal, electric and magnetic energy, both temperature and velocity fields in the arc region and in the weld pool were exhibited. Results show that about 10% of plasma arc outflows from the keyhole exit. The heat conduction flux is more than two times of the electron condensation flux in the welding process. It is also found that the Marangoni shear takes obvious priority over the electromagnetic force, and two circular flows appear in the weld pool. Moreover, arc flows, electrical potential, current density and electromagnetic force were all predicted to further the understanding of thermal plasma process. Two velocity-transition points were found within the keyhole, from which the arc begins to flow outwards and upwards and finally outflows through the top metal surface. Finally, experiment was conducted on the stainless steel plate, and the measured weld pool is close to that calculated by our model.