Purpose: This paper aims to examine the precision loss of ball screw raceway under different operating conditions and geometry parameters. Design/methodology/approach: Based on a new coefficient K’ introduced especially for ball screws to reflect the actual contact condition, the modified Archard theory is applied to ball screws to obtain wear volume of the ball-screw contacts. Thus, the axial precision loss can be defined as the ratio of the wear volume to the contact area. Meanwhile, a novel running bench and a precision-measuring system of ball screws are conducted. Precision variation is obtained and analyzed during the whole life running test, which agrees well with the theoretical values calculated in this paper. Findings: For a given rotational speed, the increasing rate of the precision loss rate is high at low axial load and then becomes small with the increasing axial load, whereas for a given axial load, the precision loss rate is proportional to the rotational speed. Besides, the precision loss rate is reduced with the increasing contact angle between a ball and the screw raceway, and is proportional to the helix angle when the angle changes from 1 to 10 degrees. Research limitations/implications: The rotational speed used in this experiment is low and the ball screw is of no-load type, although results calculated by the model and Wei’s model seem close when the axial load is high, whether the model built in the paper is applicable to the condition of high rotational speed and preload still needs to be verified in the future work. Practical implications: This study provides an accurate model to predict the precision loss of the screw raceway and estimate the remaining life of ball screws, which is significant for better performance of ball screws as well as the computer numerical control machine tools. Originality/value: Previous studies on the wear of ball screws mainly focused on the drag torque analysis and mechanical efficiency estimation, and the experiment to verify their theoretical analysis was almost all limited to the test of drag torque or axial rigidity, which is neither sufficient nor persuasive. However, in this paper, the authors proposed a comprehensive wear prediction model which combines the modified Archard wear theory, Hertz contact theory and kinematic theory of ball screws. To the best of the authors’ knowledge, this kind of study has never been reported in the literature. In addition, for the lack of the test bench and high cost of the experiment, the whole life operation test, which is designed and conducted to confirm the model in this paper, has never been reported in literature either.

Owing to the measurement difficulty and the required time needed to analyze wear processes of ball screws, very few studies have been reported. Here, on the basis of a test bench and a Taylor Hobson surface profilometer, the measuring procedure for the raceway surface profiles of ball screws was proposed first. Then the raceway surface profiles of a typical ball screw were measured after 1.42 million running revolutions. Finally, a combinational method including the statistical parameters, recurrence analysis, and fractal dimensional was used to characterize the lubricated wear process. Results show that the increase of the surface roughness (Ra) and maximum peak-to-valley height (Rz) can be up to 396% and 395%, the recurrence rate can decrease more than 59%, and the ratio between the minimum and maximum values of the fractal dimension can be 77% after 1.42 million running revolutions. Further analysis showed that the three methods all reflected the raceway wear dependence on the number of revolutions, and the linear correlation of the fractal dimension method with the number of revolutions was the strongest, which provides a new way to predict the wear states of ball screws by monitoring the worn states of the raceway surface profiles.

The coefficient of friction (COF) is a key factor to estimate the performance of ball screws. Pieces of research focus on the experimental study of the COF, leading to the COF chosen empirically in many studies. To acquire the COF of the ball screw, a measuring system is conducted to detect the friction torque under different preloads and rotational speeds and the effects of the applied axial load and rotational speed on the COF are analyzed. By the curve fitting method, the Stribeck curve of the ball screw is obtained. The experimental results show that the lubricating state can be divided into two categories: the mixed lubrication state and the elastohydrodynamic lubrication state. This study is beneficial to choose a suitable working condition for a different performance of the ball screw.

With the development of rolling linear guide manufacturing, improvements of performance and reliability of rolling linear guide products have become the critical technical challenge. One of the key-points lies in the analysis of wear process, in which the crucial step depends on the computation of the wear coefficient. However, little attention has been devoted to the wear coefficient of rolling linear guide. Therefore, in this article, to reflect the actual working condition of rolling linear guide, a novel calculation model for the wear coefficient of rolling linear guide is established first through theoretical analysis. And then, based on a novel loading bench and a friction measuring device, the wear process and wear coefficients of a rolling linear guide (DA45CL) were obtained and analyzed. Further analysis shows that the wear coefficients obtained in this article, which are several orders of magnitude less than the previous empirical values, are more reasonable for the wear analysis of rolling linear guide. The current work provides a new theoretical and experimental method to investigate the wear coefficient for rolling linear guide, which is meaningful for the study of the wear process of rolling linear guide and other rolling components of computer numerical control (CNC) machine tools.