Material Transfer Behavior During The Process In Friction Stir Welding

Considering the practical geometry of rotational tool and the relation between thematerial properties and temperature, transfer behavior of welding plastic metal is obtained bythe ANSYS FLUENT software while the metal of weldment is7075aluminum alloy. In thesimulation, the plane shoulder, the inner-concave-flute shoulder and theconcentric-circles-flute shoulder are studied. On basis of Friction Stir Welding experimentalmethod, transfer behavior of welding plastic metal is obtained. And the effect of weldingparameters on flow behavior of plastic material is also analyzed.The simulation results show that when the shoulder of the tool is plane, the biggestvelocity appears at the edge of the shoulder. When the rotational tool with the left screw pinrotates clockwise, the flow direction of material near pin is downward while the flowdirection near the thermal–mechanical affected zone is upward, which is opposite to that ofthe right screw pin. For the change of tool shoulder geometry nearly has no effect on the trendof material flow. For the material flow velocity, the value under the condition of theconcentric-circles-flute shoulder is the biggest while the value under the condition of planeshoulder is the smallest. From the view of avoiding the root defect, the rotational tool withconcentric-circles-flute shoulder is better than the tool with inner-concave-flute shoulder,which is verified by experiment. The flow velocity of material inside weldment is increasedby decreasing the cone angle of pine or decreasing the width of screw groove. Therefore,choosing the reasonable shoulder geometry and the reasonable pin geometry can be good forimproving the material flow during the friction stir welding process and avoiding the rootdefects. On basis of preliminary research work, a new kind of rotational tool which is madeup of the one-spiral-flute shoulder and the rotational pin with right screw is designed. Theresults show that this kind of rotational tool is better for materials flow.The simulation results show that with the increase of the rotational tool’s speed, thematerial flow velocity increases and the region which material flows strongly also enlargesand the effect of welding speed on material flow is not obvious for changing the welding parameters.The experimental results show that the material which is near the surface of weldmentflows downwards while the material in the middle of weldment flows upwards and also at thisposition the transfer displacement of plastic metal is the biggest. And the transferdisplacement of plastic metal at the bottom of weldment is close to zero. The transferdisplacement of plastic metal on the retreating side is bigger than that the advancing side.With the increase of welding speed, the transfer displacement of plastic metal will decrease.While the transfer displacement of plastic metal increase, with the increase of rotational tool’sspeed.