Research On Reliability Allocation Of CNC Machine Tools Based On Fault Correlation

With the rapid development of China's equipment manufacturing industry today,how to speed up the modernization of the equipment manufacturing industry has become a major task facing the country.The CNC machine tool is known as the manufacturing industry's "industrial machine",and its reliability level is particularly critical.Therefore,to improve its reliability,it is of great significance to carry out in-depth research on the reliability allocation of the CNC machine tools.The field data show that the fault independence hypothesis can not reflect the actual operation status of the CNC machine tools,and the established reliability allocation model has some deviation.Therefore,how establishing a fault correlation reliability allocation method has become an urgent problem to be solved.The thesis takes the CNC machine tool as the research object and mainly completes the following research work:First,establish the reliability model of the CNC machine tool subsystem based on fault correlation.Bootstrap and maximum likelihood methods were used to estimate the parameters of the distribution model.Based on the operation and maintenance data and structural characteristics of the CNC machine tools,the fault correlation among subsystems of the CNC machine tools is analyzed by using the fault directed graph and adjacency matrix.Based on the influence of failure rate,the reliability model of the fault correlation subsystem is derived.The Pagerank algorithm was used to optimize and analyze the impact degree of subsystems,and the reliability models of each subsystem were obtained.The accuracy and validity of the fault correlation subsystem reliability model were verified by the D test difference,relative error,and accuracy factor.Second,Failure Mode Effects and Criticality Analysis of the CNC Machine Tools based on Euclidean Distance.In view of the difficulty in identifying the key subsystems of the CNC machine tools,the fault location analysis,fault mode analysis,and fault cause analysis are used to conduct qualitative and quantitative analysis of the CNC machine tools,to determine the key subsystems of the CNC machine tools and identify the weak parts.To effectively solve the problem that the hazard equivalents cannot be sorted due to the weight of each index in the risk priority number method,the fault vector is introduced to carry out the hazard analysis based on Euclidean distance,which provides the basis for further reliability allocation.Third,A reliability allocation method based on fault correlation is proposed.The harmfulness,complexity,maintainability,and importance of subsystems are taken as the influence indexes of the CNC machine tool reliability allocation,and the weight of subsystems directly affects the allocation results.In this paper,the distance function is used to optimize the weight of each indicator to reduce the subjective randomness and IEW-VIKOR(Information Entropy Weight,IEW;Vlsekriterijumska Optimizacija I Kompromisno Resenje,VIKOR).Combined with the fault correlation theory,the reliability distribution of the CNC machine tools was carried out.By comparing the results of independent,equal,and AGREE on fault allocation,the reliability allocation based on fault correlation can effectively guarantee the reliability requirements of the system,and reduce the reliability requirements of each subsystem.The results of reliability allocation based on fault correlation can effectively reduce the cost of reliability design and provide theoretical guidance for further reliability improvement.