Research On Performance Reliability And Optimization Strategy For CNC Machine Tool Spindle System

With the rapid development of the equipment manufacturing industry,the reliability of CNC machine tools has attracted more and more attention from the public.The spindle system is a key subsystem of CNC machine tools,and its both thermal characteristics and dynamics characteristics determines largely the reliability of CNC machine tools.In case of the relevant parameters of spindle system can not be controlled properly in the process of design and manufacturing,which may lead to reduce the reliability of spindle system.To explore the key common technology for improving reliability of the spindle system of CNC machine tools,the dissertation is supported by the National Science and Technology Major Project of China(Grant No.2013ZX04011-011).The object of this dissertation is a certain model of homemade spindle system for the CNC machine tool.The influence of the randomness of relevant parameters for spindle system on its both thermal and dynamics characteristics as well as their performance reliability is adequately considered.In order to further study on thermal and dynamics characteristics of spindle system,the effect rules of relevant parameters on the stiffness and heat generation for a combined set of angular contact ball bearings in the spindle system is investigated.And on this basis,thermal-structural coupling analysis of spindle system is done based on finite element method,to research on both the reliability and the sensitivity of thermal tilt for spindle system.Dynamics model of spindle system is established by the method of lumped mass while the dynamics characteristics of spindle system and both the reliability and the sensitivity of vibration for the front of the spindle are studied in more detail.Finally,the optimization strategy of thermal-dynamics characteristics for spindle system is presented.The research contents and its results are as follows:(1)Taking the combined set of bearings at the front of spindle system as a research object,the equations for both the stiffness and the heat generation of DBD combination of angular contact ball bearings are established based on quasi-statics analysis and raceway control theory of the rolling bearing.On this basis,the influence of the preload and the rotational speed on both the stiffness and the heat generation for the combined set of bearings is analyzed,the results show that the rotational speed has a rare effect on radial stiffness for both single bearing and the combined set of bearings,but preload has a significant influence on the stiffness for the combined set of bearings.Axial stiffness for both single bearing and the combined set of bearings have an increasing trend with the increase of rotational speed.The heat generation of sliding friction of spinning roll element decreases with the increase of preload for the combined set of bearings.The researches provide a theoretical basis to analyze thermal and dynamics characteristic of spindle system.(2)The influence of the mean and variation of structure parameters on the sensitivities of both the stiffness and the heat generation for angular contact ball bearings is simulated using a combination method of Kriging model and Monte Carlo random sampling method.The results show that the mean and variation of structure parameters for angular contact ball bearings have an adverse effect on the sensitivity of the axial and radial stiffness.The stiffness and heat generation for the bearings are the most sensitive to the variation of ball diameters.This researches bring forward the theoretical basis for selecting the design parameters and machining accuracy of bearings as well as separation of parts.(3)Thermal-structural coupling coupling finite element analysis model for spindle system is established by using ANSYS software,to research on the thermal characteristics of spindle system.The reliability and sensitivity for the thermal tilt of spindle is calculated using a combination method of MCMC and responde surface,the strictly controlled parameters of bearings group for improving the reliability of the thermal tilt of spindle are obtained,and this study provides theoretical evidence for improving the reliability of the thermal tilt of spindle.According to the experimental data of thermal errors based on the five points method and the temperature of thermal sensitive points for spindle system,thermal error prediction model of spindle system is established using wavelet transform and support vector machine(WT-SVM).This research provides a technical support for spindle thermal error compensation technology.(4)A nonlinear vibration analysis model of CNC lathe spindle with ten freedom degrees is established,which considers elastic spindle stiffness,damping and nonlinear contact force of rolling bearing.And the nonlinear dynamics characteristics of spindle system is analyzed.The reliability of dynamics performance of spindle-rolling bearing system and its sensitivity to correlated random variables are studied.The results show that spindle system occurs The radial clearance of bearings in the rear bearing group and the total contact stiffness of spindle system should be optimized firstly in designing spindle system.The studies provide a theoretical reference for improving dynamics performance and reliability design of spindle system.(5)The preload and bearings structural parameters of the rear bearing group in the certain model of homemade spindle system for CNC machine tool are optimized using a combination method of Kriging model and multi-objective particle swarm optimization,which can obviously reduce the number of design points and increased bearing design efficiency.