关键词: 无缝钢管, 壁厚偏差, 推压缩径, 周向褶皱, 端部翘曲

Abstract:  Circumferential winkles in inner wall of tube end during pushing diameter-reducing production practice would seriously affect the quality of parts. The wall thickness of seamless steel tubes was measured， and the distribution law of wall thickness along circumferential direction was alternately thin and thick. A mechanics model of pushing diameter-reducing of tubes with wall thickness deviation was established. The stress and deformation in reducing， rounded corner and exit stage were analyzed， and the generation mechanism of circumferential winkles at the ends was obtained. Four times pushing diameter-reducing tests of tubes with different wall thickness deviation were carried out. Results show that the end unevenness is greater than the initial one, and the sizing area unevenness is less than the initial one， which are consistent with theoretical analyses. The influence laws of wall thickness deviation and reducing times on unevenness and relative unevenness were summarized， and the ranges of process parameters for producing circumferential wrinkles were given. A geometrical model of tubes with wall thickness deviation was established， where the inner surface shapes were periodic sinusoidal variation and the outer surface shapes were circle. The generation and development of circumferential winkle were  simulated， the evolution laws of wall thickness and relative unevenness in each stages were obtained. Simulation results show that  theoretical analyses are consistent with the tests. By means of pushing-pulling diameter-reducing， the end unevenness and warpage may be greatly reduced， and the forming quality may be effectively improved. 

Key words: seamless steel tube, wall thickness deviation, pushing diameter-reducing, circumferential wrinkle, end warpage