带壁厚偏差管大变形推压缩径端部周向褶皱研究

Investigation on End Circumferential Wrinkles of Large Deformation PushingDiameter-reducing Tubes with Wall Thickness Deviation

无缝钢管推压缩径生产中的端部内壁周向褶皱会严重影响制件质量。通过测量无缝钢管壁厚,发现壁厚沿周向分布存在薄厚交替性变化规律;通过建立带壁厚偏差管推压缩径力学模型,分析管坯在减径、圆角及出口区的应力及变形特征,得到端部周向褶皱的生成机理。进行不同壁厚偏差管四道次推压缩径试验,结果表明端部不平度均大于初始不平度、定径区不平度均小于初始不平度,与理论分析吻合;总结了壁厚偏差和缩径道次对不平度、相对不平度的影响规律,并给出了产生周向褶皱的工艺参数范围。建立内表面为周期性正弦变化、外表面为圆形的壁厚偏差管几何模型,模拟出周向褶皱的生成与发展过程,得到壁厚、相对不平度在缩径各阶段的演变规律,模拟结果与理论分析吻合、与试验结果趋势一致。采用推压-拉拔缩径,可以大幅降低端部不平度和翘曲,有效提高成形质量。

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.