3D profile bending with five controlled degrees of freedom

Abstract

In the recent decades, several processes for kinematic bending of tubes and profiles to three-dimensional contours have been developed. Although these processes offer the potential to cope with current demands for natural aesthetic design and high flexibility, they are not yet widely used in the industry. One reason has been, until now, the lack of fundamental knowledge about the forming process itself – specifically the forces and torques acting on the profile during 3D bending and the resulting stresses and strains in the cross-section.

In order to generate a comprehensive understanding of the mechanics of 3D bending, first, the geometrical characteristics of 3D-shaped profiles are analyzed. Subsequently, the controlled degrees of freedom (cDOFs) process kinematics need in order to produce 3D shapes are derived. This groundwork is used to set up a 5-cDOF profile bending process with integrated force and torque sensors. Additionally, a new kind of contact-based contour measurement device is developed that allows time-efficient analyses of 3D profile shapes.

A curved elastic model is created, which is able to accurately model in-plane springback and the interaction of torque and bending force components. During the analysis of the plastic profile behavior, equations are set up that describe the reciprocal effects of axial and shear stress and are used to calculate the bending force and torque acting on a profile during 3D bending.

The geometric relation of profile shape and bending kinematics is finally used together with the elastic and plastic analyses to set up a comprehensive process model, which can accurately simulate the profile behavior during 3D-profile bending and can be used to generate spring-back compensated NC-data for bending processes with 3-6 cDOFs.