| Friction stir welding technology is widely used in the welding between dissimilar metals and high polymer due to its advantages of wide application of materials and high welding efficiency.With the deepening of the research of friction stir welding technology,many achievements have been made in the problems of weld ability,process parameter optimization and numerical simulation.But at present,the optimal design of stirring pin is mostly carried out by experiment and intuition,which has many problems.In order to solve this problem,numerical simulation and experiment were combined to investigate the relationship between the morphology characteristics of the stirring pin and the flow behavior of the plastic metal regularly,and to optimize the design of the stirring pin.The numerical simulation model of temperature field in friction stir welding of 6061-T6 aluminum alloy was established,and the temperature field of the stirring pin with the combination of concentric shaft shoulder and threaded conical stirring needle was simulated.The temperature field and temperature distribution of friction stir welding with this shape stirring pin were studied.The influences of shaft shoulder and stirring on temperature distribution were analyzed respectively.The causes of asymmetry of temperature distribution in front and back of stirring pin,forward and backward side of welding direction were discussed.The finite element analysis model of flow field in friction stir welding was established based on computational fluid dynamics.The flow field of concentric circular and threaded conical stir pin was numerically simulated.The flow behavior and velocity distribution of plastic metal were studied,and the causes of asymmetry and eddy current formation were analyzed.On this basis,established with thread cone type and take three pyramid type two kinds of stirring needle,spokes,vortex and shoulder blades type,in view of the shoulder blade type,detailed research the influence of the number of blades and blade groove width,through the flow chart,the velocity vector diagram and statistical values of velocity distribution and evaluation standard,has carried on the comparative analysis.The results show that the conical agitator needle with screw thread and the shaft shoulder with six fan blades have the best stimulating effect on metal flow.The influence law of the change of the geometric characteristics of the shaft shoulder and the stirring needle on the flow behavior of the plastic metal material is obtained,which provides a way of thinking for the evaluation of the influence of the stirring pin on the flow behavior of the plastic metal.The friction stir welding experiments of aluminum alloy to aluminum alloy and aluminum alloy to PC were carried out by using the designed stirring pin and the conventional stirring pin.Under the two sets of parameters,the weld surface forming conditions and the mechanical properties of the welded joints of the two stirring pins were compared and analyzed.The results show that the design of the stirring pin can significantly improve the weld surface forming.In terms of mechanical properties,the tensile strength of the welds obtained by the design of the stirring pin experiment is increased by 7.88 MPa compared with the conventional stirring pin,which is 15.62% of the tensile strength of PC. |
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