Investigation On The Reliability Design Of Feed Drive System For CNC Machines

NC machine tools are the basic device to modern manufacturing industry,which are the manufacturers with the high-technology.Whether the advanced functional machine tools that have the high machining precision and reliability are the criteria for measuring the level of a country's manufacturing standards.At present,comparing to NC machine tools made by technique developed countries,the gap of the function and precision level decreases,but Chinese ones have relatively low level of reliability.The relative lower level of machine tools industry in our country,therefore it is necessary to improve the reliability of domestic machine tools and key functional parts.To carry out the reliability design for machine tools and key functional parts is one main way to improve the reliability of machine tools.As key functional part of NC machine tool,the feed drive system influence on machine accuracy of machine tool remarkably.So it is necessary to improve the reliability and estimate the reliable life of the feed drive system.It is of great significance to explore a method of life prediction that based on science,no matter in theory or practice,the load spectra are the foundation of reliability design and life prediction.Differences between the load spectrum of CNC lathes and mechanical structures are obvious,because of the instability of the load time history of CNC lathes.In order to study the method of establishing the load spectrum,this paper is based on the cutting experiments of CNC tools,and combined with relevant research.The main contents of the paper as follows:(1)Analyze the failure mode and effects on Feed Drive System of CNC Machines,list the functional block diagram of Feed drive system,analyze the failure mode and cause of feed drive system and its failure influence,and come to FMEA statistics.(2)Establish the dynamic model of Feed Drive System of CNC Machines.The feed drive system is processed into Euler Bernoulli beam system with mass block.The dynamic model was established by finite element method.And the contact deformation of bearing,ball screw and rolling linear guide is treated as the spring-damping model.The axial vibration and torsional vibration of the ball screw and the table are considered comprehensively.According to Lagrange equation,the motion differential equation of the feed drive system is established.(3)Study on the method of loading spectrum for NC machine tool feed system.The method and process of load spectrum of feed system for NC machine tool are described,according to Distribution hypothesis,parameter estimation,fitting inspection on,load data,load spectrum of Feed force of feed system is obtained.Using the established dynamic model of The feeding system with feed force as the input of the system,The relationship between the axial vibration displacement and time of the screw,the relationship between the axial vibration acceleration and the time of the screw is analyzed by computer simulation,then according to the Hertz contact theory to calculate the relationship between load and time of ball.Establish working table and linear rolling guide dynamic model,similarly obtained the relationship between the horizontal load and time and the relationship between the vertical load and time,obtained the track by the changes in the relationship between the friction force and the time of linear guide rail.Finally,according to The relationship between load and time,the reliable life prediction of ball screw and linear rolling guide rail is carried out.After this paper,we believe it will provide the foundation for the reliability design of the CNC lathe feed system in the future.