Influence of deformation zone length on bending radius of SS304 tubes with small diameters manufactured via free bending-based active motion

In three and six-axis free-bending equipment, the deformation zone length (A) is a fixed mechanical structure parameter modified when the relevant structure is redesigned and manufactured. In this study, a six degree of freedom (6-DOF) parallel mechanism was used as the control mechanism of the bending die, and a new method of changing the deformation zone length (A) was proposed. Firstly, an idealized geometric model of free bending-based active motion was established. Then, the influence of the deformation zone length (A) on the bending moment and the bending radius of the tube was analyzed. In addition, the finite element simulation and a kinematic model of free bending-based active motion controlled by the 6-DOF parallel mechanism were established, and bending processes of the SS304 tube with different deformation zone lengths were investigated. Afterwards, the impact of the deformation zone length (A) on the bending radius, bending moment, wall thickness, and motion of the parallel mechanism were analyzed. Finally, experiments were carried out on the free-bending equipment based on the 6-DOF parallel mechanism. Experiments verified the rules in the theoretical analysis, finite element simulation, and kinematic simulation.