Modeling buckled developable surfaces by triangulation

In the first stage of sheet metal stamping, a binder ring, an annular surface surrounding the die cavity, clamps down on the flat blank, bending it to a developable binder wrap surface which may be smooth or buckled. Buckles generally appear in the binder wrap when the binder ring does not lie on a smooth developable surface that spans the die cavity. However, sometimes buckles can improve the formability of the stamped part, so the ability to design buckled developable surfaces becomes desirable. Designing buckled developable surfaces requires geometric modeling of creases and other singularities in the interior a flat sheet. In this paper we review the properties of such surfaces, show how to approximate buckled binder wrap surfaces by developable three-dimensional triangulations and discuss the insights gained from specific examples.