Study of axial force and bending moment in tube numerical control bending based on finite element method

To understand forming mechanism and analyze springback after unloading, and to select equipment and design die, it is necessary to obtain axial force and bending moment during the numerical control (NC) bending of tube. In this paper, a method of obtaining axial force and bending moment in tube bending process based on simulation results of the process using finite element method (FEM) has been put forward. Key procedures of this method have been represented in detail. Using the method, the features of axial force and bending moment in tube bending process, and influence laws of rotary velocity, bending radius, strength factor and hardenability value on axial force and bending moment have been obtained. The results show that: during tube bending process, axial force acting on plastically deforming area changes a little, and bending moment acting on the area increases like an exponent line; axial force acting on rigidity end of the zone undergoing bending deformation increases linearly, and bending moment acting on the zone varies like a damped sine curve; the increase in rotary velocity and strength factor of material, and the decrease in bending radius and hardenability value will lead to the increase in axial force and bending moment. The method proposed in this paper also can be generalized to other bending processes of other parts, such as blank, profiled bar and tube.