Research On Bearing Wear In Spindle-Bearing System

Spindle-bearing system is the core functional component of CNC machine tools,wear is one of the main failure forms of spindle bearings.It is of great significance to study the wear of spindle bearings for evaluating the operation accuracy and predicting the service life of CNC machine tools.The operating conditions of spindle-bearing system include high-speed light load and low-speed heavy load.Under the two conditions,the load of bearing and motion characteristics are significantly different,which leads to significant differences in wear law of the bearing.The research on wear law of bearing under the two conditions is of great significance for optimizing CNC machine tools and prolonging the service life of CNC machine tools.In this thesis,the spindle-bearing system is taken as the research object which supported by four angular contact ball bearings,and the spindle-bearing system model and bearing wear model are established.The effects of spindle speed,external load,bearing angular misalignment,raceway curvature coefficient and bearing surface roughness on bearing wear are compared and analyzed under high-speed light load and low-speed heavy load conditions.The main contents include:(1)The mechanical model of spindle-bearing system with multi bearing support and the wear depth model of bearing raceway are established.The system model includes bearing model and spindle model.The hypothesis of "raceway control" is abandoned,and the influence of centrifugal force and gyroscopic moment of rolling element is considered.The quasi-static model of bearing is established.Applying the finite element method,the Timoshenko beam element is used to establish the spindle finite element balance equation.A fast and reliable solution method for the spindle-bearing system model is proposed,and the validity of the system model is verified by comparison.Based on Archard wear model,considering the load and velocity distribution characteristics of rolling element and raceway,a wear model suitable for the calculation of raceway wear depth of rolling bearing is established.(2)A comparative study of the bearing wear laws in the spindle system under high-speed,light load and low-speed and heavy load operating conditions.The contact force,average sliding speed,wear coefficient and wear depth of each bearing in the spindle system are calculated under different spindle speed,external load,bearing angle misalignment,raceway curvature coefficient and bearing surface roughness;the similarities and differences of bearing wear law under high-speed light load and low-speed heavy load are compared and analyzed.The results show that: the spindle speed has a significant impact on the bearing wear;the change rate of bearing raceway wear depth with the speed is greater,under low speed and heavy load conditions;regardless of the working conditions,the ideal installation of the bearing is the most favorable for the operation of the spindle;under the condition of high-speed and light load,the change of spindle speed significantly affects the change rate of bearing raceway wear depth with external load,but under the condition of low-speed and heavy load,the change rate of bearing raceway wear depth with external load is less affected by spindle speed;under the two conditions,the change degree of bearing raceway wear depth with raceway curvature coefficient is significantly different;the increase of surface roughness can significantly increase the wear depth of each bearing in the spindle system.