Research On Robot Friction Stir Welding Control System And Welding Process Of 1561 Aluminum Alloy

IIIWith the proposal of China's "Ocean Power" strategy,lightweight and large-scale shipbuilding has become a new development trend.1561 aluminum alloy has good corrosion resistance and high specific strength.It is a high-quality material for manufacturing large aluminum alloy ships.When welding aluminum alloys for ships,the fusion welding method is easy to cause pores and cracks in the joint,and the friction stir welding(FSW)method is widely used in aerospace,shipbuilding,electronic power and other industrial fields due to its solid phase connection advantages.In recent years,in order to solve the special FSW requirements of marine aluminum alloy workpiece with complex shape,robot FSW equipment has been introduced in China.However,this equipment can only use constant position control mode for welding at present,which is prone to uneven welding seam pressure caused by joint deformation.Therefore,robot FSW equipment control system is studided in this,the FSW of 1561 aluminum alloy was realized by constant pressure control method,and analyzed the mechanical properties and microstructure of the joint,providing theoretical basis for improving the joint quality.This paper mainly completed the following work:The control system of robot FSW equipment was studied.PLC + HMI +frequency converter was adopted to set up the electrical control system,PC +PLC AI/AO module + sensor converter was adopted to set up the constant pressure control system on robot FSW equipment,the constant pressure control robot FSW welding process was realized,with the parameters that the maximum pressure of the equipment was 12 k N,the highest rotation speed was 6000 rpm,and the fastest welding speed was 2 m/min.By verifying the technological performance of robot FSW system,constant pressure control mode and oncentric ring shoulder welding tool were selected as marine aluminum alloy FSW.In FSW of curved workpiece,the weld surface was well formed.FSW process of 1561 aluminum alloy was studied by single factor and process optimal experiment,the results show that the improper selection of process parameters will lead to insufficient pressure depth,grooves and flying edges on the weld surface,internal hole and non-penetration defects.When the process parameters was800-200-10,the maximum tensile strength of the joint was 358 MPa(91.6% of BM);the micro-hardness of the joint was distributed in a W shaped pattern,with the highest hardness value of BM and the lowest hardness value of HAZ near TMAZ.On this basis,the model equation between the process parameters and the tensile strength of the joint was established by using the response surface method,and the optimal process parameters was predicted to be 700-150-9.5,the corresponding joint tensile strength was 364.47 MPa(93.2% of BM),and the actual test results was 362.8 MPa(92.8% of BM).The prediction accuracy of the model equation was high.The microstructure of joints in different areas was studied.The results show that the BM grains were rolled and the average size was 6.0 ?m,the HAZ grains grew with heat,and the average size was 10.9 ?m,partial dynamic recrystallization occurs in TMAZ,the grains were elongated and directional,and the average size was 6.8 ?m,dynamic recrystallization occurs in SZ,the grains were fine and equiaxed,and the average size was 4.0 ?m.When approaching from BM to SZ,the proportion of subgrain boundary decreases successively,and that of large-angle grain boundary increases successively.In BM grains,there were a large number of tiny dislocation cell structures;in TMAZ and SZ,dislocation walls and subgrain boundary structures were found.According to the grain boundary orientation difference distribution,the dislocation density decreases gradually when the transition from BM to SZ occurs.Deformation strengthening and fine grain strengthening were the main strengthening methods of the joint,and the HAZ side near TMAZ on the forward side was a weak zone of mechanical properties.The results show that the robot FSW equipment with integrated control system in this paper,it can meet the requirements of all-position FSW welding of marine aluminum alloy workpiece with complex shape.Through the FSW welding test of1561 aluminum alloy and the analysis of the mechanical properties and microstructure of the joint,it can be shown that the constant pressure control FSW welding method can effectively improve the joint quality,which lay the foundation for the next promotion and application.