Research On Dynamic Characteristics Of Angular Contact Ball Bearing In Feed System Of CNC Lathe Under Variable Speed Conditions

Angular contact ball bearing is an important part of the feed system of CNC lathe to support the ball screw,and its performance directly determines the performance and life of the whole machine.With the development of CNC lathe in the direction of high speed,high precision and long life,the problems of bearings such as the deformation,slip,collision,vibration,noise,temperature rise,and running smoothness decrease have become more and more acute,which have a great impact on the operation precision,reliability and service life of the feed system.However,because angular contact ball bearing have complex internal motion relationship and many non-linear factors under non-stationary operating conditions,its dynamic characteristics under variable speed conditions have not yet been clarified,which has become a difficult problem in the rolling bearing research field.Therefore,it is of great significance to carry out research work on the dynamic characteristics of angular contact ball bearings under variable speed conditions for improving the dynamic performance of rolling bearings.And it can provide a theoretical basis for the high-speed and high-precision development of CNC lathes and other mechanical equipment.In this paper,taking angular contact ball bearing 7603025 of the longitudinal feed system of GSCK200 A CNC lathe as investigation object,and combining with the working principle and structural characteristics of the angular contact ball bearing,the dynamic characteristics of the angular contact ball bearing under start-stop and speed fluctuation conditions were studied by theoretical analysis,simulation calculation and experiment.The main research contents including:(1)According to the working principle and structural characteristics of the angular contact ball bearing,the contact stiffness relationship of two contacts was established and the internal load distribution characteristics of bearing under different loads were obtained.Based on the bearing geometrical relationship,the kinematic relationship of internal components of the angular contact ball bearing were acquired.(2)Based on the theory of multi-rigid system dynamics,using the Impact Function Method and Coulomb Method to simulate the internal contact relationship of the bearing,a multi-rigid dynamic model of the angular contact ball bearing 7603025 was established by ADMAS.The effects of radial load,axial load and angular acceleration on the dynamic characteristics of the angular contact ball bearing under start-stop conditions were studied,which are the speed and centroid motion of cage,and the contact force between rolling ball and cage.The results show that the increase of radial load and the decrease of axial load leadto loading of rolling ball more uniformly,and the increase of angular acceleration causes the load on rolling ball to not enable the ring to guide it to pure rolling motion when the angular contact ball bearing start and stop,which will result in the increase of the bearing skidding,the increase of the contact force between rolling ball and cage,and the deterioration of the stability of cage.(3)Based on the basic theory of explicit dynamics,using Linear Elastic Material Model and Symmetrical Penalty Function Method to simulate the contact deformation of the bearing,a multi-flexible dynamic model of the angular contact ball bearing 7603025 was built by ANSA and solved by ANSYS/LS-DYNA Solver.The dynamic performance of the bearing under different speed fluctuation types(sinusoidal fluctuation,rectangular fluctuation and random fluctuation)conditions were analyzed.The effects of fluctuation parameters(fluctuation amplitude and fluctuation frequency)on the dynamic characteristics of the bearing were studied,which are the speed and centroid trajectory of cage,the centroid trajectory of inner ring,the contact force between rolling ball and inner ring,and the contact force between rolling ball and cage.The results show that the fluctuation form of cage speed is determined by the inner ring speed;Moreover,the greater the fluctuation amplitude of the inner ring speed,the larger the fluctuation amplitude of the cage speed,and the greater the fluctuation frequency of the inner ring speed,the larger the fluctuation frequency of the cage speed;In addition,the greater the fluctuation amplitude and fluctuation frequency of the inner ring speed,the more severe the shaking of inner ring,the larger the contact force between rolling ball and cage,and the more disordered the centroid trajectory of cage.(4)A rolling bearing test bench was designed and built,and the cage speed of the bearings were measured and compared with the simulation results,and the vibration characteristics of the angular contact ball bearing during start-stop process were studied experimentally.The results show that the simulation results are in good agreement with the experimental results,which verifies the validity of the dynamic model of the angular contact ball bearing.During the start-stop process,the smaller the radial load and axial load,the greater the angular acceleration of inner ring,the larger the vibration acceleration of the bearing and the vibration of the stop process is more severe than that of the start process.