Study On Forming Limit And Numercial Simulation Of Double Sided Pressure Hydrofroming

With the exacerbation of energy shortage in the word-wide, the internationalautomobile industry accelerates the pace of automobile lightweight, more and morematerial with light weight, high strength but low plasticity is applied in automobileindustry for the reason, so study on the forming of this high strength, low plasticitymaterial has a lot of practical senses.Double sided pressure hydroforming is a newly forming technology. The principleof it is that: let the two sides of metal sheet full of liquid with initial pressure throughout,the sheet are hydroformed by the pressure difference of the two sided. The purpose ofapplying the double side pressure hydroforming is to improve the deformation zone'sstress state, lubricating state and the evenness degree of deformation for the promotion ofthe forming limit.Firstly, the paper analyses the reasons of inaccuracy forming limit prediction by thetheoretical FLD in forming low plasticity material with double stretch deformation;describing the ductile fracture criterion(DFC) which bases on damage effect mechanicsand the applications of the ductile fracture criterion in the sheet metal forming limitprediction. All those provide the demonstration of applying the DFC for predicting theforming limit of the double sided pressure hydroforming in next text.The paper deduce the stress, strain and thickness distribution of the part which isformed by the double sided pressure hydroforming. Then getting it's effective stress andstrain distribution by combining the Hill yield criterion and D.Drucker harden materialflow criterion.At last, the double side pressure hydroforming process of the approximatesemi-sphere parts with material of LY12(M),LF21 and st17 is numerically simulated bythe FEM software ANSYS/LS-DYNA. Generating the elements' fracture appreciationprogram by using object oriented language Visual C# .The program which combines thesimulation results data and DFC, gives the forming limit height at different initial liquidpressure p0 with different material. Drawing the limit height curves at different initialpressure, they show that the limit height of the forming could be promoted by increasinginitial the liquid pressure p0 , and when the initial liquid pressure p0 approaches to thestrength of the material, the effectiveness is obvious. The double sided pressurehydroforming simulation results of the conical box parts show that the hydroformingcould improve the friction conditions and decrease the deformation between materiallayers;numerical simulating the viscous pressure forming(VPF) by controlling up anddown sided pressure field in different areas of the sheet, the results show that VPF cancontrol the deformation subsequence of the sheet, make the deformation more uniformand release the local thickness reduction of the sheet.