The numerical simulation of stretch flange forming

Simulations of stretch flange forming operations are undertaken using expli cit dynamic finite element calculations utilizing various quadratic and non -quadratic yield criteria. Both circular and square cut-out blanks are inve stigated with corresponding circular and square punches. Simple stretch fla nges are considered, utilizing a single punch to expand the cut-out, as wel l as z-flanges, which employ a back-up punch to form the second bend needed in the z-flange profile. Results from a model of an automotive inner compo nent incorporating a cutout with stretch flange corner features are also pr esented. Predictions utilizing the Barlat-89 criterion are shown to accurat ely capture the effect of yield anisotropy (R-value). The predicted strains from the corner regions of square cut-out stretch flange laboratory specim ens are shown to be similar to those within the automotive inner panel, sup porting the use of laboratory-scale stretch flange experiments to simulate the larger panels. Measured limit strains from the stretch flange formabili ty experiments are compared to forming limit diagram (FLD) data from dome s pecimens. Stretch flange formability is shown to exceed allowable levels pr edicted using a classical FLD approach, particularly for simple stretch fla nges, indicating that the FLD approach is overly conservative. (C) 2000 Els evier Science Ltd. All rights reserved.