Analysis On Static And Dynamic Characteristics Of The Spindle System For A NC Lathe

High-speed and high-accuracy are the trends in the development of CNC machine tools.As one of the key parts of NC machine tool,the spindle system has a direct impact on the machining precision and efficiency of NC machine tools.As an important support part of the spindle system,the static and dynamic characteristics of rolling bearings will have a crucial impact on the performance of the spindle system.However,in the traditional theoretical method,the influence of the dynamic characteristics of the bearing on the system is neglected,and the coupling of each factor is not taken into account.Therefore,the article uses HTC2050i CNC machine tool spindle system as the research object.Firstly,the article analyzes the dynamic parameters such as dynamic stiffness of double-row cylindrical roller bearings and double-row angular contact bearings,and then considers the interaction between them.After that,the dynamic model of the spindle system is established and the static and dynamic characteristics of the object are also studied.Specific content is as follows:Based on Hertz line contact theory and elastohydrodynamic lubrication theory,the static model of cylindrical roller bearing under pure radial load is established,the static characteristic parameters of the bearing are also solved numerically and the influence of radial load and bearing structure parameters on the static characteristic is also studied.Then the dynamic model of cylindrical roller bearing,which includes bearing dynamic load distribution model,contact dynamic stiffness model,oil film stiffness model and dynamic stiffness model of bearing considering Four directions of combined loadings and the effect of lubrication,is established.On the basis of the established mathematical model,the dynamic characteristic parameters of the bearing under radial load are solved by Matlab software.And the dynamic performance of the bearing is analyzed and studied.The influence of the bearing internal parameters and working conditions on the dynamic performance of the bearing is discussed.Based on Hertz point contact theory,the static model of angular contact bearing under pure axial load is established,and the static characteristic parameters of bearing are numerically solved.The influence of axial load and bearing structure parameters on the static characteristics of bearing is also studied.Then the dynamic model of angular contact bearing,including the ball motion model,the ball bearing model,the bearing force balance model and the dynamic stiffness model considering the 5 directions of combined loadings is established.Based on the established mathematical model,the dynamic characteristic parameters of the bearing under axial load are solved by Matlab software.The contact angle between the ball and inner and outer ring,contact load between ball and inner ring and outer ring and dynamic characteristic of bearing dynamic stiffness are analyzed and summarized.Based on the finite element method and Timoshenko beam theory considering shear deformation,the dynamic model of the spindle system is established.The influence of the dynamic stiffness of the bearing and the gyro moment of the shaft are considered in the model.The natural frequencies and modes of the system are obtained by Matlab.The Campbell diagram of the spindle system is drawn and the critical speed of the system is obtained.Then the three-dimensional model of the spindle system is established and the model is simulated by Ansys software.The numerical results are compared with the simulation results,and the results are within the allowable error range.Finally,the change of the dynamic characteristics of the spindle system caused by the speed is studied,and the influence of the rotation speed and the gyro moment on the dynamic characteristics of the system are analyzed.