Investigation of Warping and Springback in Kinematic U-Profile Bending with Partial Heating

A new method to reduce warping and springback for kinematic bending of arbitrary profile geometries, which are frequently used in transportation applications, is presented. The warping occurs naturally in such processes due to a misalignment of the force initiation axis and the shear center of the profile. Warping is commonly prevented by using restrictive tools, which in turn reduce the process flexibility. Springback is usually compensated through overbending. However, if the regular forming process is designed close to the forming limit, overbending might not be an option. The proposed solution involves a partial heating of the profile. In this case the base of a U-shaped profile is heated. As a result, the position of the shear center is shifted in the direction of, or, at best, to align with the force initiation axis. At the same time, the heating helps to reduce springback due to thermal softening. Three-roll-bending experiments on U-profiles made of S500MC are used to describe the warping and springback behavior in the unloaded state after bending. With these experiments an FEM model is validated. The model is used to investigate bending moments and shear stresses in the profile during bending. Results indicate that by partial heating, warping can be reduced by up to 76% and springback by up to 48% compared to the values for bending at room temperature.