Physical Modelling Of The Plastic Flow In The Friction Stir Welds

In this paper, the material flow for friction stir welding process was explored usingplaticine as analog. The flow driving force and influence of the tool shape on thematerial flow were analyzed, via the observation of the marker platicine distribution indifferent weld sections and stressed state of the platicine; finally, the results of physicalanalogue have been compared with the aluminum friction stir weld. Further, high-speedvideo flow visualization in friction stir welds of PVC was used to the verification of theplaticine analog.The results showed that the platicine on the upper part of the weld took acontinuous smearing-like movement with the viscous force of the shoulder. Whensmooth pin was used, the material around the pin moved with the rotation of the pinunder the viscous force of the pin, the process showing a vortex-type flow pattern.While, when the threaded pin was used, the strength of the upper part material withright threaded pin cases was much larger than the left threaded cases. In the weld whenthe left/right threaded pin was taken, the downwards/upperwards extrusion of screwthread on the plasticine caused the materia along the pin took a downwards/upperwardsspiral movement. During the processing, the plasticine dropped away continuous fromthe tip/root of the pin and finally accumulated and generated an extrusion area at thebottom/top of the weld. Meanwhile, part of the plasticine under the visco force of thepin moved around with the rotary stirring of the pin then filled the transient cavitybehind the pin.Visualization experiments indicated that the stirring action of the smooth pinbrought the migration of the entire material backwards to the transient cavity in thespirally movement. When the threaded pin is concerned, the movement round the pinstill exists. when the left srew is used, the sucking effect will occurred and the Adhesionellipsoid will generated at the bottom of the weld, whereas, when the right screw is usedit will happened at the top, while the material accumulated on the weld top experiencedthe “smearing-like” movement and filled the transient cavity before it could be formedadhesion ellipsoid.It came to conclusion that the identical characteristics on the welds of plasticine and of metal demonstrated that the results of physical simulation can be accuratelyapplied on the platic flow behavior of metal welding，and the transparent PVC sheetvisualization experiments demonstrated the correctness of the physical modeling of thePlastic metal flow pattern using plasticine in friction stir welding.