Method On Design, Manufacturing And Wear Property Of Electronic Current Aided Friction Stir Welding Tool

The research was from the project named heat affect and microstructure changingregularity of Electronic current aided Friction Stir Welding supported by NationalScience Foundation of China (51075413).Electric current aided Friction Stir Welding (EFSW) was proposed for a problemexisted in conventional Friction Stir Welding due to insufficient heat production, whichhas limited its welding scope. As one of the key technologies of EFSW, there exist aclose relationship between the tool design and the microstructures and mechanicalproperties of the joint. During FSW processing, the tool will bear a combination of hightemperature, upsetting force, friction torque and welding resistance. Long time workingwill lead to the failure of the tool and further shorten its service life. Friction wear is thekey factor to affect the FSW tool’s life, and it’s also one of the main failure ways. Thewear of the FSW tool will seriously lowing the welding efficiency, arising theproduction cost and shorten the lifespan. The electric current aided Friction Stir Welding(EFSW) has combined the advantages of resistance welding and friction stir weldingand creatively formed a new hybrid heat source welding technique, which is expected toimprove the working condition of tool. In this article, tools of EFSW were designed andmanufactured, and then the experiment and simulation work on them was investigatedby taking ZK60magnesium as welding material.Five tools with various geometries were designed and manufactured by additivemanufacture technology, named flat shoulder and threaded column pin with4slidingfaces (1#), flat shoulder and threaded column pin (2#), concave concentric groovesshoulder and taper threaded pin with concentric grooves (3#), concave shoulder andtaper threaded pin (4#) and concave shoulder and taper threaded pin with3slopes (5#).The loads situation of the tool was analyzed at idealization case. And the results showthat the tools only bear the normal stress along the axis and the friction torque in theopposite direction of the tools rotation. The normal stress and friction torque isincreasing with the welding depth. At the welding stage, besides the stress and torqueexerted on the forward lateral section of the pin, the friction stir welding tool also bearthe resistance force in opposite direction of welding and its generated bending moment.The loads exerted on the tools in stable welding stage are only concerned with the sizeand geometry of pin and shoulder. The tool’s optimization experiment shows that microstructures of TMAZ inadvancing side and retreating side show obvious differences due to different heat historyand mechanical action. Joints obtained by2#tool under two welding speed have smoothappearance, little flashes, fine and uniform microstructure in WNZ and the bestmechanical properties.The orthogonal test method was adopted to evaluate the effects of rotation speed,welding speed and electrical current on mechanical properties (tensile strength andelongation) of the joint fabricated by EFSW. The results show that electrical current hasremarkable influence, and then are rotation speed and welding speed on turn. TheANOVA of experiment data indicates that effect of electrical current and rotation onjoint quality is significance under the condition of significance level set at0.2.Optimized process parameters of EFSW were rotation speed1400r/min, welding speed72mm/min and electrical current30A. When optimized parameter was taken inexperiment, the tensile strength of the joint can be82.6%of BM, and the elongation isup to5.36%.The effect of electric current on EFSW tool wear during the welding of ZK60magnesium alloy was simulated based on Archard wear theory. And the results indicatethat the maximum wear depth of5tools is decreasing when the electric currentchanging from30A to150A. The maximum wear depth of tools with column features(1#,2#) is larger than those with conical features (3#,4#,5#) under different electriccurrent, and its reducing rate has experienced a changing process from relatively rapidto gentle. A wear ring zone was generated on the outer indent surface of4#and5#tool’sshoulder due to a sufficient contact with plastic material.Resistance generated heat during EFSW can improve the welding temperature,reducing flowing stress, strengthening plastic material fluidity and decreasing therelative slide velocity between EFSW tool and welding material. So the mechanicalloads and wear of the tool during EFSW can be reduced effectively.