The mechanism of compression and bending coupling effects on cross-sectional distortion under boosting conditions

Abstract Push-Assist is commonly used to inhibit the thinning defect in the bending forming of aerospace tubes, but it tends to introduce distortion defects. The compression effect generated by Push-Assist is a type of inhomogeneous compression, which forms a coupled superposition effect of bending and inhomogeneous compression during the tube bending forming process, thus exerting a relatively complex influence on distortion. Therefore, this study theoretically analyzed the superposition mechanism of the compression effect of Push-Assist and the bending stress of the tube, and established a theoretical model of tube distortion under bending-compression conditions. By using the finite element simulation method and experimental verification method, the characteristics of tube distortion under different Push-Assist parameters were analyzed. The research conclusions show that: (1) The axial compression effect generated by Push-Assist at low speeds (v ≤ 0.9v 0 ) has an inhibitory effect on bending distortion. The friction force of Push-Assist can generate a certain amount of compressive stress, which weakens the tensile stress on the outer wall during the bending process and thus effectively inhibits the cross-section distortion of the tube during bending. (2) An excessively high Push-Assist speed (0.9v 0 < v ≤ 1.1v 0 ) will aggravate tube distortion. This causes the tensile effect at the contact part between the lower side of the tube and the anti-wrinkling die to be gradually amplified, thereby further aggravating tube distortion. (3) The Push-Assist effect can enhance the tube’s forming limit. Under the condition where the Push-Assist speed is 0.9v 0 and the friction coefficient μ at the contact surface between the pressure die and the tube is 0.4, the difference between the best and worst tube forming quality under the Push-Assist condition is 20.6%, with a 10.68% reduction in the maximum distortion rate of tube forming compared to the non-Push-Assist condition.