Sringback Prediction In Multichannel Forming Of Ultrathin Stainless Steel Sheet

Microforming is widely used to manufacture all kinds of micro parts because of its high producing efficiency,high utilization of material,thus there is enormous market potential to produce micro parts using microforming technology in many fields.Springback is the inevitable elastic release phenomenon after the load is removed in sheet plastic deformation process.It is the main problem occurs in sheet forming and seriously affects the size precision and shape precision of sheet parts.In microforming process,with the decreasing of part feature size,springback phenomenon shows remarkable size effect,traditional bending springback theory can't been directly applied to the springback of micro sheet forming process anymore.Conducting researches on the rule of sheet foil springback behavior and the process control methods considering the influence of size effect is significantly important.This paper focus on the springback prediction and control in micro sheet forming process,SUS316 L stainless steel sheet metal is employed.Various heat treatment experiments are conducted to obtain specimens with different grain size,then the uniaxial tensile test is conducted to obtain the mechanical property of material,conducted microbending experiments,the effect of different process parameters on springback angle is then studied.Established the constitute model based on composite model,proposed a springback prediction method based on the proposed model taking the size effect into consideration,based on the proposed model,he effect of different process parameters on springback angle is studied.Designed a pair of microchannel forming mould,conducted multichannel forming process experiment,furthermore,using the developed PEMFC plate mould,the multichannel forming experiment is conducted and the distribution of channel height is studied,the FE model of multichannel forming is established and the effect of different parameters on the height is studied.The main research work is as below:(1)Microbending experiments of SUS316 L sheet and results analysisObtained specimens with different grain size using different heat treatment process,the uniaxial tensile test is conducted to obtain the true strain-true stress curves.The effect of grain size on the mechanical property of material is analyzed.a group of microforming mould is designed and manufactured to conduct pure bending and stretch-bending experiments,then the microbending experiments is carried out to study the rule of microbending of micro sheet metal.Furthermore the effect of grain size,the punch radius/grain size ratio and strain condition on springback of micro sheet bending is analyzed,the springback angle increases as the t/d ratio decreases,the springback angle increases as the punch radius increase,and the tensile strain condition can significantly reduce the springback amount of micro sheet.(2)Proposed a springback prediction method considering size effect and analyzed the effect of process parameters on springback angleBased on the composite model,the constitute model considering size effect is established,and verified its precision using FE simulation method.Based on the traditional springback theory,the prediction model of micro sheet considering size effect is then derived,and the calculated springback angle shows fine agreement with the experiment results,the precision of this new method is verified.Using the obtained prediction,the effect of bending radius,grain size and elastic modulus on springback angle is analyzed,the springback angle decreases as the grain size grows,the springback angle increases with the increasing of bending radius,the springback angle decreases with the increasing of elastic modulus.The distribution of feature height is studied to provide guidance in microchannel manufacturing process.(3)The springback process study in the multichannel forming process of ultrathin sheetThe multichannel forming mould is designed and manufactured,the experiment is conducted to study the forming rule in multichannel forming process and the effect of punch radius on channel height in multichannel forming process.The multichannel experiment with channel number in large scale in further carried out using the PEMFC plate forming mould designed by our group,the distribution of channel height is further studied,in the width direction,the height of inner channels is smaller than that of the external channels,and the variation increases as the overall forming height decreases.Moreover,the multichannel forming FE model is established based on plain strain theory to study the effect of punch radius?clearance and friction coefficient on the distribution rule in multichannel forming process,which provides important guidance to the manufacturing of PEMFC plate.