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Numerical Simulation of Rotational Tool Shoulder Shape’s Effect on Transfer Behavior of Welding Plastic Metal in Friction Stir Welding

The plunging process of rotational tool is simulated while the shapes of rotational tool shoulder are inner-concave-flute, concentric-circles-flute and three-spiral-flute respectively. The effect of rotational tool shoulder’s shape on transfer behavior of welding plastic metal is obtained. The results show that whatever the shape of tool shoulder is, the metal of contact surface in the workpiece undergoes relatively big plastic transfer. To the rotational tool with three-spiral-flute shoulder, the transfer velocity and displacement of plastic metal inside the workpiece slowly decrease with the increase of the distance away from the surface of workpiece. To the rotational tool with the inner-concave-flute shoulder or the concentric-circles–flute shoulder, the transfer velocity of metal inside the workpiece is very small and the value is close to zero. Using the rotational tool with no pin, the experiment of friction stir welding is processed. The results show that the size of every grain in weld nugget zone which is made by the rotational tool with three-spiral-flute shoulder is nearly the same. The degree of uniformity of grain made by three-spiral-flute shoulder is much higher than that made by inner-concave-flute shoulder or concentric-circles-flute shoulder.