42nd International Deep Drawing Research Group Conference - IDDRG 2023

A developable surface is one that can be flattened into a plane without distortion. Thin sheet metal is often treated as a developable surface. The classical theory of folded developables proves that curved crease, origami-style folding can be applied to thin sheet metal of high strength to manufacture parts with rather complex geometries. However, its applications are found to be limited to sheet metal with low-medium strength and adaptation of various thickness accommodation techniques like grooving or perforation of the material at the fold lines. Removing material at the fold lines facilitates curved axis bending of rigid materials having finite thicknesses. Applying the geometrical concept otherwise, although has attractive applications in sheet metal intensive industries like automotive and transportation, remains unexplored. The current study tests the applicability of the theory of folded developables without compromising material integrity at the fold lines, by combining it with a traditional sheet metal forming technique called flange drawing. Following the theory, a developable connection is successfully achieved with a thin sheet metal material of high strength and reasonable inextensibility, without using any thickness accommodation techniques. However, it is found that the findings of the classical theory do not hold true for bending sheet metal having a finite thickness. The shape of the formed developable is not identical to the initial shape. Unique shape defects like curving and coning are identified. Additionally, a modified strain measurement method revealed significant membrane strains in the plane of the formed developable. A geometrically perfect model overestimates the magnitude of strains obtained analytically. Therefore, material properties and related effects like springback cannot be ignored as they not only influence deformation in the geometrical process, but also the shape of the final part. This knowledge adds value for designing future processes to manufacture complex sheet metal parts from developable shapes, using conventional forming techniques.