Numerical Simulation Of Three Dimentional Plastic Metal Flow Of Friction Stir Welding

Three dimentional flow of the plastic weld metal is the critical factor for the formation of the friction stir welding joint. The finite element software ABAQUS is used to establish three dimentional coupled thermal-mechanical plastoelastic FE model of friction stir welding with unthreaded conical tool. And then the temperature field, equivalent plastic strain field of7075aluminum alloy friction stir welding are simulated by using the numerical model, the plastic metal flow pattern is simulated by using material displacement tracer particle method. Based on these, the three dimentional weld metal flow characteristics during friction stir welding by using unthreaded conical tool and the influence of the process parameters on the weld metal flow are analysed.The research results show that, during friction stir wlding, the peak temperature of the weld is82%of the melting point of the base material, the temperature grandient on the advancing side of the weld are bigger than that on the retreating side, and the temperature grandient of the weld in front of the tool are bigger than that behind the tool. Plastic strain happens in the welded region behind the tool. The plastic strain on the advancing side of the wld is bigger than that on the retreating side.In the welding process, the weld metal, close to the upper surface of the weld, rotates clockwise around the pin under the friction and forge of tool shoulder. Whereas, the weld metal close to the lower surface of the weld moves clockwise to the back side of the tool under the rotating forge of the pin. The weld metal from advancing side of the workpiece depositeds dispersely at the center and the advancing side of weld behind the tool, only little part of the weld metal deposites at the retreating side. The weld metal from the retreating side of weld is forged to the back side of the tool in the pattern of curve like laminar flow, and then deposites at the retreating side, part of the weld metal close to the upper surface of the workpiece deposites at the advancing side behind the tool after rotating several circuits. Weld metal in front of the pin mainly deposites dispersely at the advancing side behind the tool, only little part of the metal deposites at the retreating side.During welding process, material from upper and lower surfaces of the workpiece doesn’t move in the through-thickness direction, part of the weld metal from the a d v a n c in g si d e, r e a ti n g si d e a nd le a d in g si d e of th e w e l d r o t a t e s do w n a n d d e p o si t e su n d e r th e in f lu e n c e of th e to o l, th e w e ld me ta l whi c h di d n’t d e p os i t e f o l l o w s th e ot h e rw e ld me ta l to r o ta te u p to th e r e g io n c lo se to th e u p pe r su r f a c e o f t h e w e ld.T h r ou g h r e d u c in g w e ld in g sp e ed w h il e th e r o ta ti n g s p e e d o f t he to ol k e e p in gc o n st a n t, w e ld me ta l f r o m th e adv an ci n g, r e tr ea ti n g a n d le a d in g s i d e o f t h e w e ld mo v e sa t f a st e r sp e e d to th e r e g io n b e h in d th e to o l, at th e sa me ti m e, th e tr a ns p o r ti n g e xt e n t in th e th r o u gh-th ic k n e ss di r ic ti o n o f th e w eld me ta l f ro m th e s e t hr e e r e g io ns r e d uc e s. T h r ou g h in c r e a si n g r o ta ti n g sp e ed o f th e to o l w it h th e w e ld in g sp e e d ke e p in g c o n st a n t, w e ld me ta l f r o m th e se th r e e r e g io n s d ep o si t e s fast e r to th e r e g io n b e h i n d th e to o l, a n dsi m u lt a n e o u sl y th e tr a n sp o r ti n g e xt e n t o f th e w e ld m e t a l i n t he t h r ou g h-th ic k ne ss d ir ic ti o n r e d uc e s.