Freeform Bending Tool Design for Rectangular Profiles and Its Influence on the Process

Abstract

Freeform bending offers a wide range of possibilities in terms of component geometries, material grades, and profile cross sections. In the field of circular solid and hollow profiles, the circular shape of the profile used determines the design of the tool. When using rectangular profiles, the cross section of the tool cannot be easily obtained by an offset of the profile cross section. The large tolerance ranges of the profile standards like wide ranges of corner radii or material thickness require compromises with regard to the shape and tolerances of the tool. Currently, there are no design guidelines for freeform bending tools and no approaches as to whether universal tool approaches or specialized tool approaches should be used for freeform bending of rectangular profiles. This concerns both the geometric dimensions regarding clearances and the functional design of the tools, for example, rollers or sliding tools. Tests have shown that the design of the tool has a great influence on the quality of the component. Clearances that are too wide to accommodate the tolerances can result in larger wrinkling and buckling. Clearances that are too tight can lead to increased scrap because parts of a batch may not fit into the tool. Furthermore, the trade-off in the tool design can lead to tool shapes, which encourage further defects. These are mainly wrinkling, cross-sectional deformations, and strongly deformed profile corners, which in some cases form cracks in the material. In this article, the influences of the tool design on the bending of rectangular profiles and the resulting defects of the profiles are investigated. For this purpose, experiments were carried out utilizing several tool designs with different variants and four combinations of the movable die and the fixed die. Each configuration was used with the same calibrated kinematics to investigate several different radii and compare the results. The experiments show that the design of the tool has a direct influence on the bending result and also an influence on the development of bending defects. The hypothesis that the effect of increasing defects is caused by increasing friction is shown experimentally, explained theoretically and confirmed with an additionally built simulation model.