| Hybrid journal bearing is an important application in high precision CNC machine tool spindle system.The design of reasonable bearing structure parameters and the selection of appropriate bearing operating parameters are of great significance to the optimization of bearing characteristics and the improvement of spindle performance.In this paper,a high-precision lathe spindle symmetrical step recess hybrid bearing as the research object,its performance and its influencing factors are studied in depth.Firstly,based on the integral difference method,the theoretical analysis model of the hybrid bearing is established to solve the dimensionless oil film pressure of the symmetrical step recess hybrid bearing and study the static characteristics of the bearing.Then computational fluid dynamics simulation method is used to study the influence of bearing operating parameters on bearing characteristics.Then the unsteady Reynolds equation is solved and the dynamic characteristic coefficients of the bearing is calculated by the difference method.Finally,the dynamic and thermal characteristics of the bearing-spindle system are analyzed.The main contents of the paper are as follows:(1)On the basis of reviewing relevant literatures at home and abroad,the latest progress in the research on the structure and bearing characteristics of journal bearing and the current research status on the dynamic and thermal characteristics of the spindle system are reviewed,and the research contents and methods of the subject are determined.(2)The two-dimensional stationary Reynolds equation is discretized by the integral and difference method,and a mathematical model suitable for solving the pressure of shallow step recess bearing is established.Considering the flow balance equation of the deep oil cavity,the boundary conditions of the deep oil cavity are obtained,and the mathematical model suitable for solving the hybrid journal bearing pressure in the deep and shallow recess is obtained.(3)Based on the theoretical analysis model of hybrid journal bearing,the establishment method of the new symmetrical step recess hybrid journal bearing oil film analysis model is studied.Then,the dimensionless pressure distribution,flow rate,bearing capacity,offset angle and other characteristic parameters of the forward and backward rotating bearing are solved to study the influence of bearing structure parameters on its bearing capacity,and the oil film characteristics of symmetrical step recess bearing and unilateral step recess bearing are compared and analyzed.(4)Using computational fluid dynamics simulation,the bearing oil film is taken as the calculation domain to calculate the oil film pressure,oil film temperature rise,bearing capacity and other characteristics of symmetrical step recess bearing.The influence of bearing speed and oil supply pressure on bearing bearing performance is analyzed.(5)Based on the unsteady two-dimensional Reynolds equation,the difference method is adopted to calculate the stiffness and damping coefficients of the bearing.The dynamic simulation of the spindle is carried out in the finite element analysis software,and the modal,critical speed and unbalanced response of the spindle are solved.(6)Finite element analysis software is used to analyze the thermal characteristics of the lathe spindle,and the heat from the bearing oil film calculated by CFD is applied to the spindle system to solve the steady-state temperature rise cloud diagram and structural deformation of the spindle box and spindle.Compared with experimental data,the feasibility of simulation analysis is verified.In this paper,the hybrid journal bearing of the spindle of high-precision CNC lathe is taken as the research object,the method of establishing the bearing bearing characteristic model of symmetrical step recess is studied,and the influence of different structure parameters and operating parameters on the static and dynamic characteristics of the bearing is studied.The influence of dynamic characteristic parameters of bearing on dynamic characteristic of spindle system and the influence law of bearing temperature rise on thermal characteristic of spindle system are also studied.The research results provide a reference for the design of hybrid journal bearing and have certain guiding significance for improving the running accuracy and stability of machine tool spindle. |
