Study On Dynamic Characteristics Of Paired Installation Angular Contact Ball Bearings-Rotor System

With the rapid development of advanced manufacturing technology,high-speed cutting machine tools characterized by high efficiency and high precision have become the core industry of high-speed machining in equipment manufacturing industry.Therefore,as a key component of high-speed cutting machine tools,the speed and stability of bearing-rotor system are required to be higher and higher.How to improve the critical speed of the spindle is an urgent problem to be solved.In this thesis,the paired installation angular contact ball bearing-rotor system of a spindle is taken as the research object.Aiming at the critical speed and stability of the rotor system,the quasi-static analysis model of the diagonal contact ball installed in pairs is established,and the dynamic characteristics of the paired installation angular contact ball bearing are analyzed in detail.On this basis,the finite element model of paired bearing-rotor system is established by Timoshenko beam theory.The effects of bearing stiffness,preload and gyroscopic moment on the whirl frequency and critical speed of the rotor system are analyzed.The unbalanced response of the rotor system is further studied,which verifies that the spindle with paired bearings as support has higher stiffness and critical speed.The main research contents are as follows:(1)Static analysis of angular contact ball bearings.Through the static analysis of single angular contact ball bearing under combined load,the radial,axial and angular displacements of the inner ring of the bearing are obtained,which lays the foundation for the dynamic analysis of angular contact ball bearing.(2)Dynamic characteristics analysis of paired installation angular contact ball bearings.Firstly,Hertz contact theory and quasi-static analysis method of angular contact ball bearings are expounded.On this basis,considering centrifugal force,gyro moment and radial displacement caused by centrifugal effect of bearing inner ring,and referring to the quasi-static model of single angular contact ball bearings,the analysis model of paired installation angular contact ball bearings is established.The stiffness matrix of paired installation angular contact ball bearings is obtained by MATLAB.The effects of bearing structure parameters and working conditions on the dynamic characteristics of diagonal contact ball bearings were studied.The results show that the change of bearing installation mode will affect the change trend of contact deformation,contact angle and stiffness of paired bearings.The installation mode mainly affects the angular stiffness of paired bearings,and the stiffness of paired bearings is closely related to the structural parameters and working conditions of bearings.(3)Dynamic characteristics of paired angular contact ball bearing-rotor system.Based on Timoshenko beam theory,a finite element model of a paired bearing-rotor system is established.The eddy frequency and critical speed of the rotor system are calculated by MATLAB programming.The effects of gyroscopic moment,rotor diameter and other parameters on the eddy frequency and critical speed of the rotor system are analyzed.Finally,the time-domain and frequency-domain responses of different nodes in the x-direction under unbalanced excitation force are studied.The results show that gyroscopic moment and other parameters can improve the forward eddy frequency of the rotor system,thereby increasing the critical speed of the rotor system.When the unbalanced mass exists in the rotor system,the v ibration response amplitude at the end of the shaft is the largest.