Research On Reliability Assessment And Allocation Technology Of CNC Machine

The CNC machine tool, as the basis of manufacturing industry, is an importantindicator to measure the level of manufacturing process. Its quality and reliabilitydirectly affects the development of China’s manufacturing industry. In the paper, underthe support of National Science and Technology Specific Project(2009ZX04001-81and2009ZX04011-041), and in view of the actual situation of enterprises, assessmenttechniques of CNC machine based on the Weibull distribution are developed; in light ofthe complexity of the CNC machine and uncertainty of data, the method of reliabilityallocation for CNC machine based on improved fuzzy analytic hierarchy process isproposed; failure data of CNC machine is analyzed systematically; methods ofreliability growth and management for CNC machine based on life-cycle, inconjunction with standards of enterprise management, are developed.Based on the large CNC gear hobbing machine of an enterprise, the subject mainlycompletes the following research works:①The data of CNC machine time between failures are modeled using a singleWeibull and mixed Weibull distribution respectively. Under certain domestic CNC gearhobbing machine as the research object, the reasonable testing program is selected. Alarge number of failure data are tracked and collected. The single Weibull and mixedWeibull distribution of time between failures are established by conducting these failuredata respectively. Meanwhile, the two kinds of distribution are analyzed and compared.Based on the determination of distribution model, the estimated value of the reliabilityindex of CNC machine is calculated.②In view of the complexity of CNC machine, the number of factors which affectreliability allocation of CNC machine are large, and many of them cannot be measuredaccurately, which consequently results in the difficulty of the reliability allocation. Themethod of reliability allocation for CNC machine based on improved fuzzy analytichierarchy process is proposed, which fully considers many kinds of influencing factorsof reliability allocation. The fuzzy judgment matrix is obtained by expert scoring andthere is no need to examine the consistency of the fuzzy judgment matrix. The accuracyof calculation is improved by the iterative algorithm.③The primary-secondary graph method is used to analyze the failures of thecomplete CNC machine, finding the electrical system, spindle unit and hydraulic system are the weak link in the reliability of CNC machine. In order to find the specific failuremodels and failure causes, the date of the electrical system, spindle unit and hydraulicsystem are analyzed in detail respectively. Based on the result of failure analysis,improvements of reliability design for the CNC machine are conducted partly toimporve the reliability of CNC machine.④Reliability growth and management techniques of CNC machine based on thelife-cycle are developed. According to results of the failure analysis, the reliabilitydesign criteria of mechanical, electrical and hydraulic parts are proposed. To ensure theimplementation of reliability design, the review approaches of reliability design aredeveloped. As the outside purchased and manufactured products are the most mainreasons of causing the failure of CNC machine, the guarantee measures of them arefocused and established. During the production phase, the safeguard measures of theprocess quality are proposed, especially the specific security measures of the keyprocesses. Meanwhile, the guarantee measures in the use-phase of CNC machine areestablished.