Study On Two-point Symmetric Progressive Forming Fracture Process Of 1060 Aluminum Alloy Sheet

Two-point symmetric incremental forming is an important form of sheet metal incremental forming technology,which puts two tools distributed symmetrically on single incremental forming to improve the forming condition of the sheet in the process of deformation,eventually realizing plastic process of two-point symmetric incremental forming.As two-point symmetric incremental forming has the advantages of small deformation force,uniform stress,excellent resistance to tangential distortion,good deformation quality and high deformation efficiency,and it has recently been unprecedentedly interested in the field of plastic process.But in the process of multi-point incremental forming,fracture defect is still one of the bottlenecks in the development of incremental forming technology.Therefore,it is significant to improve the forming quality by studying the fracture process of metal sheet in two-point symmetric incremental forming.This study is finished by the combination of theoretical calculation,numerical simulation analysis and forming experiment,and the main works are done as follows: After the single tensile test with different strain rate,the ductile fracture criterion of aluminum alloy sheet incremental forming is established,and the fracture process of sheet metal incremental forming is analyzed quantitatively;Based on the ductile fracture criterion,the rules of influence of forming way and forming process parameters on the ductile fracture value have been analyzed,and the related works of sheet fracture prediction and process optimization have been carried out.After the research,primary results can be obtained as follows:(1)Based on uniaxial tensile test and finite element numerical simulation,the sensitivity characteristics of 1060 Aluminum alloy sheet to strain rate during tensile process are analyzed,the incremental forming ductile fracture criterion is proposed for aluminum alloy sheet,which is considered strain rate effect;then the material parameters of ductile fracture criteria are determined by the method of finite element numerical simulation and experiment through notch tensile test and incremental forming test.(2)The finite element analysis model is established according to the process characteristics of two-point symmetric incremental forming;the ductile fracture criterion of aluminum alloy sheet incremental forming taken strain rate into consideration is used as the basis for judging fracture,based on the secondary development,the visualization of fractureprocess of sheet is realized by using finite element numerical simulation,and the fracture mechanism of sheet metal incremental forming is explored.After the results analysis,it’s shown as blow: when the ductile value reaches a certain condition,the sheet begin to crack,the correctness of the theoretical analysis results is verified further by using the finite element numerical simulation analysis method.Finally,the change of grain structure in the process of incremental forming is analyzed from microcosmic viewpoint by means of microstructure observation and analysis method.(3)The ductile fracture criterion of aluminum alloy sheet incremental forming taken strain rate into consideration is regarded as evaluation standard,the influence mechanism and law of forming way(layer processing,spiral processing)and forming process parameters(tool head diameter,feed quantity,feed speed,sheet thickness,forming angle)on fracture process and forming performance in two-point symmetric incremental forming is analyzed quantitatively.(4)Based on the forming process parameters as influence factor and the ductile fracture value as response factor,the multiple regression fracture prediction model is established through the CCD response surface method,and the optimized design of process parameters is finished,the correctness of the fracture prediction model is verified further by using forming experiment and finite element numerical simulation.As is shown from above,the research field of sheet metal forming defects is enriched and developed,and the promotion and application of sheet metal incremental forming technology in practical production have been greatly assisted.