Axial hydro-forging sequence is an emerging process to form the variable-diameter tubular components. In axial hydro-forging sequence, the excessive thickness thinning of the tube can be reduced and even eliminated by axial compression deformation. In this case, a new type defect is discovered, where the thinning of the transition zone is not decreased and a barrelling defect occurs at the end of the maximum diameter zone. To reveal the reason of the defect and provide a clue to avoid it, the stress distribution, the deformation sequence as well as the thickness distribution are investigated by mechanical analysis, finite element simulation and experiments. Two key process parameters considered in this study include the corner radius and the friction coefficient. The results show that the marked drop of the effective stress in the corner segment of the transition zone caused by the normal concentrated force is the determining factor of the defect in hydro-forging stage. It is shown that the defect can be decreased by increasing the corner radius, but only barrelling defect is decreased by improving friction coefficient. Based on the results, a new improvement approach was proposed in this paper and verified that it can effectively reduce the defect.

轴向液压锻造序列是形成直径可变的管状部件的新兴工艺。在轴向液压锻造过程中，可以通过轴向压缩变形来减少甚至消除管的过度厚度变薄。在这种情况下，发现了一种新型缺陷，其中过渡区域的变薄没有减少，并且在最大直径区域的末端出现了桶状缺陷。为了揭示缺陷的原因并提供避免该缺陷的线索，通过力学分析，有限元模拟和实验研究了应力分布，变形顺序以及厚度分布。本研究中考虑的两个关键过程参数包括拐角半径和摩擦系数。结果表明，由法向集中力引起的过渡区角段有效应力的明显下降是锻造阶段缺陷的决定因素。结果表明，可以通过增加拐角半径来减少缺陷，但是通过改善摩擦系数只能减少桶状缺陷。基于结果，本文提出了一种新的改进方法，并证明了该方法可以有效地减少缺陷。