The prediction of strip shape and restraining force for shallow drawbead systems

Computer models to predict the draw force of a drawbead assume the strip takes up the geometry of the bead as it passes through—a valid assumption for deep drawbeads, but not for shallow drawbeads. A geometric model has been used to calculate the shape of the strip passing through shallow ones. This model predicts the variation of ingress radius with a change in bead height or groove width in a constant clearance bead system. It is shown that the egress radius cannot be predicted, as an additional factor, since the strip tension must also be considered. However, the limits of the egress radius variation may be determined. The geometric model was used to formulate the correct strip geometry, which was then used as input to a previously published drawbead model to predict draw forces over a range of bead geometries for two material thicknesses and two different steels. This approach has been shown to significantly improve the predictive accuracy of the drawbead model and has extended its use to predict the draw restraint for shallow bead systems.