Han Sutao, Shu Xuedao, Shu Chang
Faculty of Mechanical Engineering & Mechanics, Ningbo University, Ningbo 315211, China.
Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208, USA.
Materials (Basel). 2018 Jul 25;11(8):1278. doi: 10.3390/ma11081278.
Considering problems about concaves at the stepped shaft ends, this paper established the plastic flow kinetic theories about metal deforming during the cross-wedge rolling (CWR) process. By means of the DEFORM-3D finite element software and the point tracing method, the forming process of stepped shafts and the forming mechanism of concaves at shaft ends were studied. Based on the forming features of stepped shafts, rolling pieces were designed using variable cone angle billets. Single-factor tests were conducted to analyze the influence law of the shape parameters of billet with variable cone angle on end concaves, and rolling experiments were performed for verification. According to the results, during the rolling process of stepped shafts, concaves will come into being in stages, and the increasing tendency of its depth is due to the wave mode, the parameters of cone angle , the first cone section length . Furthermore, the total cone section length has an increasingly weaker influence on the end concaves. Specifically, cone angle has the most significant influence on the quality of shaft ends, which is about twice the influence of the total cone section length . The concave depth will decrease at the beginning, and then increase with the increasing of the cone angle and the first cone section length , and it will decrease with the increasing of the total cone section length . Finite element numerical analysis results are perfectly consistent with experimental results, with the error ratio being lower than 5%. The results provide a reliable theoretical basis for effectively disposing of end concave problems during CWR, rationally confirming the shape parameters of billets with a variable cone angle, improving the quality of stepped shaft ends, and realizing the near-net forming process of cross-wedge rolling without a stub bar.
针对阶梯轴端部凹坑问题，建立了楔横轧过程中金属变形的塑性流动动力学理论。借助DEFORM-3D有限元软件和点追踪法，研究了阶梯轴的成形过程及轴端凹坑的形成机理。根据阶梯轴的成形特点，采用变锥角坯料设计轧件。通过单因素试验分析了变锥角坯料形状参数对端部凹坑的影响规律，并进行轧制实验验证。结果表明，在阶梯轴轧制过程中，凹坑分阶段产生，其深度增加趋势与波动模式、锥角参数、第一锥段长度有关，且总锥段长度对端部凹坑的影响逐渐减弱。具体来说，锥角对轴端质量影响最为显著，约为总锥段长度影响的两倍。凹坑深度开始时减小，随后随锥角和第一锥段长度增加而增大，随总锥段长度增加而减小。有限元数值分析结果与实验结果完美吻合，误差率低于5%。研究结果为有效解决楔横轧过程中的端部凹坑问题、合理确定变锥角坯料形状参数、提高阶梯轴端部质量以及实现无芯棒楔横轧近净成形工艺提供了可靠的理论依据。
