Experimental Study And Finite Element Analysis On Time-dependent Springback Of Typical Automotive Sheets Under Deforming

With the advancing of automobile lightening technology, all kinds of high-strength steel sheets and aluminium alloy sheets are widely applied in the manufacturing of automobile body and parts, so the formability has been paid close attention to. In addition to the instantaneous springback caused by elastic deformation, a kind of springback depending on time also exists after unloading in these two kinds of typical automobile sheets deforming, which is called the time-dependent springback.In recent years, the phenomenon of time-dependent springback and its mechanism have aroused the attention of researchers in the field of the international plastic, and relevant research and exploration ha ve proceeded. With the objects of high-strength steel sheet DP600 and aluminium alloy sheet AC170 px, aimed at the behavior of the time-dependent springback, this paper carries on studying through macroscopic tests, finite element analysis and the method of artificial intelligence. The main contents of the paper are as follows:(1) The uniaxial tension results under different different deformation conditions show that, the value of time-dependent springback after unloading goes up along with the drawing speed increase, and mainly focuses on a shorter time after the instantaneous springback, but for aluminium alloy sheet AC170 px, the effect of transition phase under the condition of rapid deformation cannot be ingored. Increasing the holding time can alleviate the growth rate of time-dependent springback to some extent, but the effect is not obvious, while the production efficiency would be reduced.(2) After the bending deformation, the value of time-dependent springback grows linearly with the increase of bending angle, and grows exponentially with the increase of bending speed. The respond of the bending time-dependent springback for AC170 px to speed is not obvious, but the value markedly increases under the bending speed of 40mm/min for DP600.(3) Based on receiving related materials viscoelastic parameters through stress relaxation and creep tests, different material models are choosed to simulate the time-dependent springback process using the finite simulaton.The updated creep model accurately describes the be nding time-dependent springback of sheets, the finite element simulation results show that releasing of residual stress is one of the reasons for driving the time-dependent springback.(4) With MATLAB platform, BP neural network is set up using time as inport and the value of time-dependedent springback as output through programming, and obtains better prediction of the time-dependent springback value at any time. Due to the dependency on sample data of BP neural network, predicting outcomes of tension time-dependent tests are more accrate. Based on the prediction, springback compensation can be set to improve the forming precision and later assembly quality of parts.