Research On Prediction Of Plastic Forming Limit Of Sheet Metal

Thin-walled metal materials,such as thin plate,thin-walled tube and thin-walled profile,are commonly referred to as sheet metal materials,which are simply referred to as sheet materials or plates.The sheet metal forming method is widely used in industries such as deep drawing,necking,bulging,flanging,bending,punching and combination.Formation is a hot research topic.In this paper,the wrinkling of 6063 aluminum alloy thin-walled tubes and the prediction of fracture defects of thin plates are studied by means of finite element simulation and experimental method.The main research work of this thesis is as follows:(1)The research status of sheet metal forming theory and forming limit diagram is summarized,and the process of sheet metal plastic forming and the defects in sheet metal forming are introduced.Some basic theories of plastic forming are expounded,four typical theories of instability judgment and theory of predicting wrinkling and buckling are described in detail.(2)The stress-strain relationship curve,strength coefficient and hardening index of 6063 aluminum alloy were obtained by uniaxial tensile test,and the material constitutive model was established.Then the axial compression experiments of quasi-static circular tubes are carried out to study the buckling mode and buckling load of different sizes of circular pipes.A reliable simulation analysis model is obtained.(3)Based on the obtained material properties and S-R theory,the forming limit diagram of aluminum alloy sheet was obtained by theoretical calculation.A method of forming limit prediction based on M-K theory and finite element analysis is proposed.The forming limit diagram of the aluminum alloy sheet is obtained,and the FLD calculated by theory is compared with the FLD simulated by finite element method.The forming limit of sheet metal under variable path is studied by finite element simulation,and the feasibility of the proposed method is verified by comparison with experiments.(4)The bulging process of thin plate and thin-walled tube are simulated by finite element method.Based on the obtained forming limit diagram,the formability of bulging is predicted.The factors influencing the wrinkling process of thin-walled pipe are studied and the measures to avoid wrinkling are put forward.