Research On Rolling Contact Fatigue Behavior Of Ball Screw

The precision and life performance of domestic ball screw significantly lags behind the imported products produced by the advanced oversea enterprises nowadays. This gap led to the inferior situation that the domestic market of high-grade ball screw products is dominated by foreign enterprises over a long period of time. What’s more, the poor performance of ball screw restricts the development of the equipment manufacturing industry in China. Thus, it is an urgent task for researchers to investigate the fatigue behavior of ball screw.In this thesis, Hertz theory has been applied into the analysis of the stress state of the contact area between ball and screw raceway. Based on the structure and size of ball screw widely used in the market, the load exerted by a single ball and maximum contact stress of the raceway under dynamic load rating was calculated. And under the present experiment condition, a new test sample was designed to simulate the contact fatigue behavior of ball screw. Meanwhile, contact fatigue strength criterion was analyzed and effort was put into the prediction of the initiation position of fatigue crack.The microstructure of crossing section cut from ball screw was observed by white light confocal optical microcopy. The hardness distribution and surface roughness of the raceway were investigated by micro hardness tester and roughmeter, respectively. The result showed that pitting, microcrack and spalling were observed successively on the raceway of samples after a certain number of cycles in the process of contact fatigue experiment. Through the observation of the initiation location and propagation angle of fatigue crack on the crossing section,45° crossing section and raceway surface, the main factors influencing the contact fatigue crack has been analyzed and the mechanism of rolling contact fatigue has been discussed.Because of the poor reliability of the tester and the design defect of sample, the none contact zone of the sample went through fracture by rotating bending fatigue in the process of contact fatigue experiment, which is seriously affected the progress of experiments. In this thesis, this fatigue fracture was investigated by electron microscopy and failure analysis. In addition, according to the existing structure of contact fatigue tester, a bearing loading device has been designed.