Reliability Test And Analysis Of Ball Screw Pair Based On Equivalent Accelerated Failure Time Model

Ball screws is an important rolling functional part of CNC machine tool,whose reliability determines the performance and accuracy of the whole machine tool.However,there is a certain gap between domestic and foreign products in reliability(accuracy,failure and fatigue life).Therefore,starting from wear mechanism,reliability index of ball screws is analyzed,accelerated reliability test,accelerated modeling and analysis based on test data are formulated and carried out.The main work is as follows:(1)The reliability evaluation indexes of ball screws are summarized and analyzed,which are divided into accuracy retention,failure reliability and fatigue life.Aiming at the accuracy retention of ball screws,the accuracy change of ball screw pair is studied from the angle of friction and wear.The wear of screw raceway is reflected by the variation of screw travel error,and the variation of friction torque reflects the comprehensive wear situation of the screw raceway and nut raceway.The wear prediction model of the screw raceway and the friction torque loss model of the double nut ball screws are established.(2)Equivalent accelerated failure time model of axial load,running speed and test frequency is established.Based on the acceleration model,two acceleration reliability test schemes of ball screws under A+A step loading of axial load at two operating speeds are developed.The range of axial stress values without changing the failure mechanism of ball screws is analyzed based on elastic-plastic mechanics.The test parameters and conditions are set up based on the actual working conditions of the ball screws,and the reliability accelerated test is carried out by selecting the samples with similar performance according to the comprehensive performance(positioning accuracy,repetitive positioning accuracy,reverse clearance,noise and temperature rise).(3)The lower confidence limits of MTBF for ball screws without failure and MTBS with travel errors and friction torque as measurement indicators are analyzed.Based on performance degradation,the degradation models of friction torque and lead screw travel errors are established,verifying the correctness of the theoretical model of friction torque loss by comparison.The equivalent accelerated failure time model are improved according to the failure life of friction torque under two rotating speeds.