| The CNC machine and basic manufacturing equipment is the foundation of achieving manufacturing technology and industrial modernization, of which performance, quality, and possession have become the important indicators of measuring a country's level of industrialization and overall national strength. Even the rapid development and modernization of CNC machine sustained nearly half a century, its reliability was always one of the crucial problems that scholars paid the most attention to solve.Because of the reliability is the primary factor that makes the development of CNC machine fast and efficient, its elevation is the emphasis of improving overall performance and technique, and the establishment of its assessment system is essential, too. A more accurate method that used for calculating the indicators of reliability is proposed after the in-depth researches on the failure analysis and assessment techniques of reliability in this subject.The papers detailed discussed the basic theories of reliability analysis of CNC machine, and ensured the method to calculate the crucial indicators of its reliability after the analysis and comparison of each method in the modeling process. To obtain the crucial assessment indicators of reliability and values of mean time between failures (MTBF) more accurately, the thesis introduced an improved gray relational method to fitting and chose better while establishing the mathematical model of reliability. The bilateral confidence interval of MTBF obeyed Weibull distribution is gained after the interval estimate of two parameters of Weibull distribution in the interval estimate process of MTBF. The method of FMECA analysis in combination with FTA analysis which is used for failure analysis of CNC machine is also proposed to identify the weak links and methods of lower the failure probability and enhance the reliability.The papers develop reliability evaluation and fault analysis system of CNC machine tools. Based on Access database technique and Visual Basic6.0 platform, the program achieved VB call to the Matlab by ActiveX automation technology, it makes the program simpler and the data processing more reliable. The modular structure used in the system mainly includes data management module, information analysis module, failure analysis module, system maintenance module, user management module and report printing module. It's not only greatly enhances the efficiency and convenience of reliability evaluation and failure analysis, but also provides an effective basis for reliability management and product improvement.The reliability of a certain type of domestic CNC lathe is evaluated by the reliability evaluation and fault analysis system of CNC machine tools software which is developed by this paper. The life distribution of CNC lathe obey Weibull distribution, obtained the reliability indexs by calculating:MTBF is 945.7738 hours; the confidence interval of MTBF is [851.79h,1029.38h]; Mean Time To Repair is 1.81 hours; Availability is 0.9984. Find out the reliability level of such domestic CNC machine tools. To finish the failure analysis of CNC lathe which are evaluated, the failure location, failure mode, failure cause and the reasons for classification of whole machine have been analyzed fistly, the quantitative analysis of FMECA of subsystem have been analyzed secondly, the spindle system which is the most harmful subsystem of CNC lathe and occurs the most failures has been found out. Then detailedly analyze the failure cause of spindle system by using FTA. Finally, suggest the improvements of the reliability of CNC lathe which are evaluated. |
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