Determination of process parameters for stamping and sheet hydroforming of sheet metal parts using finite element method
Abstract (Summary)Increase in the complexity of the parts and emphasis on the low formability and expensive lightweight materials require the use of MultiPoint Cushion (MPC) systems in modern presses and optimal blank shapes to better control metal flow and increase drawability. Programming the MPC system for forming a part is difficult and costly to estimate by trial and error FE simulation and die tryouts as there are many variable to change. Hence, multipoint cushion system available in a modern press is hardly used in practice. Estimation of Blank Holder Force (BHF) for MPC could be best done through structured FE simulations in process design stage to realize MPC system potential. Successful application of FE simulations in stamping process design depends on the accuracy of the input parameters. Sheet material properties obtained from tensile test is insufficient for the FE analysis because maximum strain obtained in uniaxial tensile test is small compared to strains encountered in stamping operations. Therefore, there is a need for a test to determine sheet material properties over larger strain range for forming FE simulations. In this study, circular and elliptical bulge test was developed to estimate flow stress and anisotropy of sheet materials over strain range, nearly twice that of tensile test for use in process simulation. The material properties obtained from bulge test was found more appropriate for process simulation compared to tensile test. Numerical optimization technique coupled with FE analysis of the forming process was developed to predict optimum BHF required to program the multipoint cushion system. The developed technique was applied to predict the BHF to form a) GM liftgate-inner, b) IFU-Hishida part by stamping process, c) 90 mm diameter round cup by sheet hydroforming process with punch (SHF-P) and d) a rectangular part by sheet hydroforming with die (SHF-D). Predicted optimum BHF resulted in parts without failure and significantly reduced trial and error effort in the investigated stamping and sheet hydroforming operations. BHF variable in space/location significantly improved the formability/drawbility compared to conventional method of BHF constant in space/location for the investigated parts in stamping and sheet hydroforming.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2007