Determination of Minimum Blankholding Pressure for Producing Wrinkle Free Products in Multistage Deep Drawing

Wrinkling in the flange region has been observed during redrawing operation by few researchers. In the present work an analysis methodology, based on a combination of upper bound and energy approaches, is proposed for the prediction of number of wrinkles and minimum blankholding pressure necessary to avoid wrinkling in redrawing operation. Thickness variation predicted by the upper bound formulation is used as input for the wrinkling analysis by assuming a suitable waveform based on geometrical and process conditions. The flange is constrained at both the ends, i.e. by the blank holder profile radius and at the die entry point (where the sheet enters into the die cavity). The waveform for present analysis is assumed such that it has zero displacement at both the ends (since it is constrained) and the maximum amplitude of the wave at some point in between those ends. The wrinkling predicted by the present methodology seems to be reasonably accurate considering the geometrical and process constraints of the redraw.