Numerical and experimental study for process improvement of cross-wedge rolling of bearing steel balls

¹ School of Mechanical Engineering, University of Science and Technology Beijing, 100083 Beijing, China
² Engineering Research Center of Part Rolling, Ministry of Education, 100083 Beijing, China
³ Shandong Zhongxing Auto Parts Ltd Company, Lixin Town, Laiwu City, 271126 Shandong Province, China

^* Corresponding author: bywang@ustb.edu.cn

Abstract

The uniaxial compression experiments were conducted on GCr15 bearing steel to obtain the flow stress curves under hot deformation conditions. Based on the results of uniaxial compression experiments, finite element modeling was conducted on the cross wedge rolling (CWR) of GCr15 bearing steel balls, and numerical simulation was conducted using Simufact Forming 16.0. The results show that the distribution of effective strain of existing CWR steel balls is uneven, which may lead to uneven quality of steel balls. In addition, the three principal stresses at the center of the steel balls are all tensile stresses, and the effective stress at the center of the middle ball is relatively large, which can easily induce central defects. Moreover, different diameter billets were used for steel balls rolling experiments. It can be seen that when the die cavity is underfilled with billet, the rolled steel balls have no central defects. When the die cavity is fulfilled with billet, there is central piercing appearing at the middle ball, while the side balls have no obvious central defects. Finally, the paper proposes the method of even numbered ball rolling (ENBR) which starts from the middle connector to improve the CWR process of steel balls.