Determination of process parameters for stamping and sheet hydroforming of sheet metal parts using finite element method

Increase in the complexity of the parts and emphasis on the low formability and expensive lightweight materials require the use of multipoint cushion systems in modern presses and optimal blank shapes. Thus, better control of metal flow can be achieved for increasing the drawability and reducing the scrap rate and manufacturing cost in sheet metal forming. The blank holder force (BHF)/cushion pin force/cylinder force required to program the multipoint cushion system for forming a part is difficult and costly to estimate by trial and error FE simulation and die tryouts as there more than one variable to change. Hence, multipoint cushion system available in a modern press is hardly used in practice. Estimation of BHF to program the multipoint cushion system could be best done through structured FE simulations in process design stage so that its advantages can be incorporated in process design and carried forward to die tryout and production to realize its potential.; Successful application of FE simulations in stamping process design depends on the accuracy of the input parameters. Conventionally, properties of sheet materials obtained from tensile test are used in FE simulation. This data is insufficient for the analysis because (a) maximum strain obtained in uniaxial tensile test is small compared to strains encountered in stamping operations (b) the stress state in tensile test is uniaxial while in regular stamping it is biaxial. Therefore, there is a need for biaxial test to accurately determine the material properties (flow stress and anisotropy constants) over larger strain range for forming FE simulations.; In this study, the issue of appropriate test method to determine material properties for process simulation, the optimal blank shape determination, and the estimation of optimum force to program multipoint cushion system were addressed. Elliptical bulge test was developed to use along with circular bulge test to estimate flow stress and anisotropy of sheet materials over a large strain range, nearly twice that of tensile test for use in process simulation. The developed test was applied to estimate properties of DP600, AKDQ, BH210 steel and A5182-O aluminum alloy. Deep drawing simulations conducted using the material properties from the developed bulge test better correlated with experiments, compared to FE predictions using tensile test data. This result indicated that material properties obtained from bulge test are 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 forces required to program the multipoint cushion system. Four possible modes for application of BHF in multiple-point cushion systems were considered, namely (a) BHF constant in space/location and time/stroke, (b) BHF variable in time/stroke and constant in space/location, (c) BHF variable in space/location and constant in time/stroke and (d) BHF variable in space/location and time/stroke. The optimum BHF was predicted by (a) minimizing the risk of failure by tearing (thinning) in the formed part and (b) avoiding wrinkling. The developed technique was applied to predict the BHF to form (a) an automotive part (liftgate-inner) from A6111-T4 aluminum alloy and BH210 steel by stamping process, (b) IFU-Hishida part from aluminum alloy A5182-O and BH210 steel by stamping process, (c) 90 mm diameter roundcup from ST14 sheet material by sheet hydroforming process with punch (SHF-P) and (d) a rectangular part from DP600 sheet material by sheet hydroforming with punch (SHF-D). Material properties obtained from biaxial tests, developed as part of this study were used in the FE simulation. Experimental results showed that the FEM based optimization methodology is able to predict the optimum BHF required to program multipoint cushion system for forming the parts without failure and significantly reduce trial and error effort in the investi...