Analysis on keyhole phase change and flow field of back reflection induced synergistic laser weld

An unified model of gas phase area, liquid phase area and solid phase area during the molten pool flow process of back reflection induced synergistic laser welding was established. Plasma & vapor cloud and keyhole absorption were considered and effects of surface tension, thermal buoyancy and gravity were taken into account in the model. The three-phase keyhole phase change and flow field of molten pool were obtained by numerical calculation, surface tension effect on flow and heat transfer of molten pool was mainly discussed. Moreover, a validation experiment of back reflection induced synergistic laser welding was carried out by taking titanium alloy sheet as an example. Results show that the coupling effect of plasma & vapor cloud caused by keyhole and back plume induced by back sub-plate is the main reason for the formation of X-type weld, and surface tension is the main driving force of the “oval reflux ring” formation in the back reflection synergistic laser welding molten pool.