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The ball screw (BS) has become an indispensable key functional component in many fields, such as CNC machine tools, precision transmission system, and special service requirements. Its accuracy reliability is a key performance in many application fields. There is a phenomenon of mixed slip-roll motion during the BS operation; however, both non-constant working conditions and mixed sliding-rolling motion mode affect its accuracy decay. In this paper, the modeling method of accuracy decay for mixed sliding-rolling motion behavior is established under non-constant operating conditions. The accuracy reliability of the BS is analyzed under single non-constant operation condition or multiple non-constant operating conditions, and the accuracy decay is predicted though modeling method proposed. In addition, the experimental analysis of the BS accuracy degradation is carried out under three different amplitudes of AL (non-constant axial load), FR (non-constant feed rate), and AL + FR combination conditions. The average value of the accuracy loss relative error (5.90 ~ 8.50%) between theoretical model and experimental test results is smaller than that (11.18 ~ 12.66%) under pure sliding motion. It shows that the accuracy decay analysis model established is beneficial to predict the BS accuracy reliability. [ABSTRACT FROM AUTHOR]

As an important precision transmission functional component in industrial fields such as large mechanical equipment, high-speed CNC machining center, and aerospace, the service life of the ball screw are directly related to the life of high-end equipment. Fatigue failure is the main failure mode of the ball screw in the transmission application where the transmission accuracy is not high. Therefore, the fatigue life of the ball screw is studied from the perspective of fatigue. The load distribution form of the double-nut ball screw under axial load is analyzed. Based on the ball load distribution, a mixed lubrication model of the ball screw considering non-Newtonian effect of lubricant is established, and a fatigue life prediction method of the ball screw based on maximum secondary surface stress is proposed. The lubrication performance of the ball screw under maximum contact load is compared with that under equal load distribution, and the effects of ball load distribution, curvature ratio, and temperature rise on fatigue life are analyzed. Two kinds of ball screw including BT GD8020 and NSK DFD8020 are used for running test of fatigue life, and the fatigue life calculation method based on the maximum secondary surface stress is verified. The hardness distribution of the transition zone between ball and raceway is analyzed, and the fatigue failure modes of two ball screws are explored. [ABSTRACT FROM AUTHOR]

Ball screw has become a key functional component commonly used in actuators of high-end machine tools because of its high transmission efficiency, low environmental impact, and strong universality of working conditions. For the high-precision ball screw, the proper and constant preload is the premise to maintain the transmission accuracy and reliable dynamic characteristics of the ball screw. The direct measurement of the preload is difficult to be achieved. Usually, the preload of the ball screw is indirectly determined by the friction torque of the ball screw under no-load condition. In previous studies, the influence of lubrication on friction torque of the ball screw was not considered, and the influence of operating conditions on performance of lubricant was ignored, and the influence of contact elastic hysteresis effect and the sliding friction effect was not considered, which seriously affected the modeling accuracy of friction torque for the ball screw. Therefore, on the basis of considering the contact elastic hysteresis friction and the sliding friction of the ball screw in the paper, a calculation model of friction torque for the ball screw based on the coupling of the ball load distribution and the thermal elastohydrodynamic lubrication is proposed. The mechanism of different friction terms on the friction torque of the ball screw is analyzed, and the coupling relationship among preload, rotational speed, and friction torque is established. The experimental results show that the proposed method, which the ball load distribution, the thermal elastohydrodynamic lubrication, the elastic hysteresis, and the sliding friction are comprehensively considered, has a good reference significance for improving the internal preload and predicting the precision degradation of the ball screw. [ABSTRACT FROM AUTHOR]

• Standard load distribution of ball screw to which turning torque is applied is a periodic shape of increasing amplitude. • Contact loads of all balls with geometric errors are bounce around the standard load distribution shape. • Axial deformation of ball screw will change constantly with all balls running in the raceway. • Variation of axial displacement caused by deformations can lead to uncertainty in transmission accuracy of ball screw. • Fatigue life of ball screw considering uneven load distribution is shorter compared to the uniform load distribution. Ball screws are the driving component used to convert rotational motion to linear motion for precision equipment and may be applied with the turning torque in practice. In past research, the contact load between ball and the raceway is assumed to be uniform wherein only the axial load is considered. This paper aims to establish a load distribution model to analyze the contact load of all balls when a turning torque caused by assembly error is applied. The axial dynamic deformation model is obtained to study the effect of the elastic creep on transmission accuracy. The authors use the kinematic analysis method to obtain the load distribution and axial elastic deformation considering the geometric errors of balls. The relationship between the introduced deformation coefficient and the defined geometric error coefficient are analyzed, and the change trend of the maximum deformation coefficient varying with geometric error coefficient is obtained. Furthermore, the position deviation and position precision of the ball screw are studied, and the fatigue life of the ball screw is analyzed based on the maximum contact load. The results show that the load distribution model considering geometric errors with the effect of turning torque proposed in this paper is a satisfactory reference to study the precision sustainability of ball screw. [ABSTRACT FROM AUTHOR]

Precision double-nut ball screws are key functional parts in machine tools. The positioning accuracy of a ball screw can directly affect the machining accuracy of a machine tools. During actual use, the preload degradation and the large axial clearance of the double-nut ball screw are caused by the contact wear, which directly affects the transmission positioning accuracy. The contact wear is focused on the ball and the rough raceway surface of the ball screw. Therefore, a novel method is proposed in this paper to characterize the rough spherical morphology of raceways for ball screws based on fractal theory, and the fractal parameters of the screw and nut raceways are identified. A fractal contact model of the asperity on the raceway surface is established. By introducing contact parameters to modify the contact area, an area distribution function suitable for the coordinated contact is obtained. A mathematical model for calculating the normal contact load of the ball screw in three states is established by considering the friction factor. A precision loss model of the ball screw is established based on the full ball load distribution model and the multiscale contact load model, and the proposed model is verified by experiments. The surface contact coefficient of the inner and outer raceways is discussed. The influence of raceway fractal parameters on the wear rate is analyzed, and coupling research on precision loss and preload degradation for the ball screw is carried out. The initial wear rate under different axial load is discussed, and the change trend of wear rate with time is analyzed. The precision loss model of the preload double-nut ball screw based on fractal theory provides a new theoretical basis for accurately predicting the precision degradation and provides method support for establishing the wear life prediction of a ball screw. • Raceway wear considering surface fractal can lead to precision loss of ball screw. • Wear volume of the work nut is different from the preload nut under axial load. • Preload of ball screw degenerates with the increasing contact wear of raceways. • Time-varying wear rate affected by operating parameters is coupled to preload loss. [ABSTRACT FROM AUTHOR]