大减径比阶梯管坯液压胀形轴向力加载方式的研究

Loading modes of axial force for stepped pipe with large diameter reduction ratio in hydroforming

针对以大减径比、轴向尺寸长阶梯管为管坯的液压胀形,理论确定了胀形管坯各区段的轴向应力,分析了轴向力作用位置对阶梯管坯直臂区及锥形区轴向应力状态和胀形区金属补料效果的影响。提出胀形初始轴向力同时作用于管坯端头及锥形区,仅作用于管坯端头和仅作用于锥形区3种轴向力加载方式。通过模拟阶梯管坯的胀形过程,揭示了不同轴向力加载方式对胀形管坯成形性的影响规律:胀形初始轴向力同时作用于管坯端头及锥形区时,管坯成形稳定性高,胀形区最大壁厚减薄量小,且成形合模力较仅作用于管坯端头方式低68.9%(较仅作用于锥形区方式低39.7%)。在普通液压机上试制出合格样件,验证了理论分析及模拟结果的正确性。

For hydrofroming of stepped pipe with large diameter reduction ratio and axial length, the axial stress in each section of bulging pipe was determined in theory, and the effects of axial force locations on stress state of straight arm and conical region for stepped pipe and feeding of bulging region were analyzed. Three loading modes of axial force were put forward including initial axial forces acted on pipe end and conical re- gion simultaneously, axial forces acted on pipe end region, axial forces acted on conical region. The bulging process of stepped pipe was simulated, and the influence rules of axial force modes on forrrkability of stepped pipe in hydroforming were revealed. When the axial forces are imposed on pipe end and conical region simultaneously, the stability of the pipe forming is high, the maximum wall thinning amount of the bulging region is snmll, and the mold clamping force is lower by 68. 9% and 39. 7% than that with the other two loading modes, respectively. The samples were manufactured on common press successfully, by which the correctness of the theoretical analysis and simulated results were verified.