 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. SEPTEMBER 2012. VOLUME 14, ISSUE 3. ISSN 1392-8716 1278 852. Study of characteristic variations of high-speed spindles induced by centrifugal expansion deformations Hongrui Cao 1 , Tomas Holkup 2 , Xuefeng Chen 3 , Zhengjia He 4 1, 3, 4 State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University Xi’an 710049, P. R. China 2 Research Center of Manufacturing Technology, Czech Technical University in Prague, Czech Republic E-mail: 1 chr@mail.xjtu.edu.cn, 2 T.Holkup@rcmt.cvut.cz, 3 chenxf@mail.xjtu.edu.cn, 4 hzj@mail.xjtu.edu.cn (Received 1 June 2012; accepted 4 September 2012) Abstract. High-speed machining has continuously pushed the demand of spindles with higher speed and higher reliability. In order to design, analyze, and test spindles in a virtual environment, accurate modeling of the spindle dynamics during the running state is essential. This paper investigates the variations of interference fit and bearing preload condition induced by centrifugal expansion deformations at high speed. Firstly, the elastic expansion deformations of the rotating parts due to centrifugal force are calculated based on mechanics of elasticity. It is found that the centrifugal expansion deformation of the bearing inner ring is much larger than the deformation of the shaft when the rotational speed increases, and therefore the amount of the interference between the shaft and the bearing decreases with the speed. Then, with consideration of the centrifugal expansion deformation, a dynamic model of high-speed rolling ball bearings is presented with experimental validation. With the proposed bearing model, centrifugal effects on the bearing preload condition are studied in detail. It is shown that the bearing contact angle decreases, while the contact load increases with the centrifugal expansion deformation of the bearing inner ring. The radial bearing stiffness increases, whereas the axial bearing stiffness decreases a little, due to the resultant effects of the decreased contact angle and the increased contact load. The preload condition of the spindle bearing is strengthened by the centrifugal expansion effect of the bearing inner ring. Keywords: high-speed spindle, rolling bearing, centrifugal effect, radial expansion, bearing preload. 1. Introduction High-speed machining technology is widely used in aerospace, automotive, electronics and many other industries. Trend of the high-speed machining has pushed the continuous demand of higher speed and higher power for machining tools. As the key component of high-speed machine tools, the spindle affects the overall performance of the machine tool. In order to design, analyze, and test spindles in a virtual environment before resorting to costly physical trials, accurate modeling of spindle dynamics is essential [1]. The rotating components of a high-speed spindle contain shaft, bearings, sleeves, etc. The joint state between each part affects the dynamic behavior and rotating accuracy of the spindle system. The angular contact bearing is still most commonly used today in high-speed spindles due to its low cost, high precision and acceptable speed limit. For the assembly of the shaft/bearing system, it is critical that the spindle shaft is always tightly fitted into the bearing bore, and therefore interference fit is applied between the bearing bore and the spindle shaft. When the shaft is pressed into the bearing, the two parts interfere with each others’ occupation of space; the result is that they elastically deform slightly, each being compressed and rotating in unison. The amount of interference is determined by rotating speeds, accuracy and rigidity of the spindle system. In practice, engineers choose the interference allowance according to bearing manufacturer’s standard, which can satisfy most needs of bearings in the range of low speed. However, at high speed, the dynamic characteristics variation of the high-speed spindle induced by speed effects cannot be ignored any more. One phenomenon is that the shaft and bearing inner ring expand radially due to centrifugal force, which leads to the change of the joint state