Friction And Wear Analysis Of A Double-Nut Ball Screw

Due to the relatively high efficiency, high location accuracy and higher automation, the application of ball screws in the defense industry, industry and agriculture has been promoted further especially in the aspects of CNC machine stools. In the 21st century, it has higher demand for CNC machine stools in speed, precision and automation. However, the speed of the domestic rolling feature high-speed development has not kept pace with the host machine and becomes the bottleneck restricting. Take the key functional component of ball screw for example, the high speed of ball screw leads to vibration, noise and friction further leads to the increase of the wear and low of the life, which greatly influence location accuracy of ball screw under the high speed condition. The development of ball screw in our country relatively late and the study of theory and experiment seriously inadequate are main reason. In order to reduce the great gaps and to solve the above problems, the roll contact theory, creep analysis and Archard model are used in this paper to analyze ball screw slipping, friction and wear. The main contents of this paper are following.1. Based on the previous research, the unified and intuitive relationship of force and motion between the coordinate systems of the ball screw by using differential transformation method is established, which is used to calculate the slip, friction and wear of ball screw.2. A new dynamic model of ball screw is developed. The model is on the basis of actual loaded between the balls in the ball screw is taken in consideration and the problem of stress inequality in every circle of a ball screw is discussed, which is not assumption that all balls were equally loaded and the loaded between balls. The obtained numerical results by the model has been proven to be reasonable and effective through the experiment.3.The slipping of the double-nut ball screw is analyzed. This analysis is not only improve the slipping between the ball and nut (screw), but also the slipping between the balls is analyzed and the centrifugal force affecting the ball under the high speed condition is also considered. The analysis of slipping affected by rotation and revolution of the ball in ball screw is been made. Through the discussion the contact angle, helix angle and screw diameter the influence to ball screw slipping, a method and measure to reduce ball screw slipping is proposed. The study results can obtained that the slipping is the main reason result in the low mechanical efficiency of ball screw.4. An improved friction model based on the rolling contact theory is established, it is compensated the Coulomb model to calculate the ball screw friction. Based on the improved friction model, the creep analysis between ball and raceway and between balls are been made and the creep parameters(including the vertical creep ratio, horizontal creep ratio, spin ratio and the slipping item of Heathcote) are obtained. Through the comparison of the measurement value by experiment and the calculated value by improved friction model, the friction model based on the creep analysis has been proven to be reasonable and effective. The relationship between creep parameters and ball screw friction and between creep parameters and friction distribution on the contact area is also analyzed.5. An improved wear model of the double nut preloaded ball screw is established by using Archard model. This model considers the influence of the centrifugal force on the ball screw under the high speed condition. Based on the improved wear model, the wear of the ball screw is analyzed, and analysis results are verified by the experiment. The relationship between the curvature ratio, the helical pitch and the screw material the ball screw wear is analyzed by using this model, meanwhile, the method and measure of improving the ball screw wear are put forward. In view of the importance and complexity of the material of the screw, and it is analyzed deliberately in order to shorten the gap in heat treatment of screw material between domestic and foreign.