The Research Of Reliability Design And Test Technology For High Grade CNC Lathes

Machine tools are the mother machines in manufacturing industry,and its development directly affects the development level of the national industry.Currently,the medium and high grade machine tools in China still have a large gap compared to foreign advanced machine tools,where the most obvious difference is the reliability.To support the implement of "High grade CNC machine tools and basic manufacturing equipment" national science and technology major project,this thesis is researched based on the project of "Reliability improvement project of thousands of domestic CNC lathes".The reliability of CNC lathe is closely related to design,manufacture,test and application.In this dissertation,aiming at the main technical difficulties,the work is mainly researched focusing design and test phases.Firstly,the reliability design and analysis of the whole machine is carried out in this thesis,aiming at the problem of the lack of reliability design of the CNC lathe at present.By using the method of maximum likelihood estimation and Edgeworth series method,the reliability model of NC lathe is established,and it's concluded that the Edgeworth series method is better for the fault interval data modeling of CNC lathe.Considering that the reliability of the CNC lathe depends on the reliability of the functional components,reliability allocation is carried out based on fuzzy entropy method.This provides the basis for the reliability requirements of the functional component suppliers.FMEA analysis is carried out for ETC series of CNC lathe machine and FMEA analysis table is established,and the potential problems of the numerical control lathe are improved.The tool holder is the key and the typical function parts of the CNC lathe.Its structure is complex,and high rotary accuracy is required.The reliability of turning accuracy has great influence on the machine tool in the application.Therefore,the reliability and sensitivity of the turning accuracy of the power servo tool holder are analyzed.The system is considered as a series system with two sub-module driving mechanism and locking mechanism by decomposing the process of transposition of tool holder.The input variable of the locking module is the output variable of the driving module.Because the turning error of the whole system is finally decided by the positioning of the locking mechanism,the tool holder is simplified and the finite element model of the three teeth disc is established.Based on the theory of artificial neural network,the function relation between the turning deviation and the design variables is obtained,and the accuracy reliability is calculated by the reliability perturbation method.In order to realize the reliability evaluation of CNC lathe,the field reliability test method based on large sample data is studied.The scheme and method of field test,the collection and processing of test data,the judgment of machine fault and the counting principle are given.The reliability evaluation indexes of NC machine tool are established.In the previously used evaluation methods,the relative weights of various indicators for evaluation are ambiguous,and all the evaluators quantify them according to their own subjective intentions after referring to various kinds of information.The evaluation results obtained in this way cannot truly reflect the reliability level,and this paper intends to introduce the entropy weight method into the evaluation system to reflect the level of reliability.Finally,the reliability comprehensive evaluation is carried out for the failure data of two kinds of CNC lathes.Finally,the reliability test devices with load for the servo tool holder and the main spindle are developed considering that the research for reliability test with load is lacking.The reliability test devices with load for servo tool holder uses servo-valve-controlled hydraulic cylinder to achieve the dynamic load.The reliability test devices with load for the main spindle uses dynamometer to achieve torque loading,and uses servo-valve-controlled hydraulic cylinder to achieve the dynamic load.The reliability test procedures of the servo tool holder and the main spindle are compiled.The reliability test with load for three servo tool holders and two main spindles are carried out and the fault data are collected.Through the analysis of their reliability evaluation indexes,the reliability level of the tested servo tool holders and the main spindles are obtained.