芯棒直径对楔横轧5Cr21Mn9Ni4 N空心气门壁厚均匀性的影响规律

楔横轧空心轴类件存在壁厚分布不均问题,特别是在小直径大长径比空心件楔横轧成形中更为突出.本文在Gleeble-1500D热模拟实验机上进行了5Cr21Mn9Ni4N耐热钢的热压缩实验,得到了5Cr21Mn9Ni4N的热变形本构方程.通过改变芯棒直径,采用有限元仿真和实验相结合的方法,研究了楔横轧轧制空心气门过程中的壁厚变化规律.研究结果表明,带芯棒轧制时,芯棒直径存在临界值,在该值下进行轧制,空心气门预制坯壁厚均匀性最优;楔横轧空心件时,金属轴向均匀流动是壁厚均匀的必要条件;轧件轴向拉应变减小,径向压应变变大,周向应变在0附近且为拉应变时,壁厚较为均匀.

Effect of mandrel diameter on the wall thickness uniformity of the hollow valve of 5Cr21Mn9Ni4 by cross-wedge rolling

Wall thickness asymmetry is a common problem for cross wedge rolling ( CWR) hollow shafts, which is especially usu-al in the CWR process of hollow shafts of small diameter and large height-diameter ratio. In this paper, the constitutive equation of hot deformation of 5Cr21Mn9Ni4N heat resistant steel was investigated by the thermocompression experiment on the Gleeble-1500D ther-mo-simulation machine. The law for the variation of wall thickness during forming 5Cr21Mn9Ni4 hollow valve with CWR was presen-ted, which is obtained via changing mandrel diameter and by means of finite element method ( FEM) and experiment. The results con-firm that when hollow valve with mandrel is formed with the CWR process, there is a critical diameter of mandrel. It makes wall thick-ness of hollow valve optimal. On the basis of FEM, it is stated that uniform flow of material along the axial direction is necessary for wall thickness uniformity of hollow valve, and circumferential stretching strain near zero, increase of radial compression strain with de-crease of axial tension strain permit to improve wall thickness uniformity of hollow valve.