Research On Influence Analysts And Growth Technique Of Credibility For Machining Center

CNC equipments are the "machine tools" of equipment manufacture, important carriersof advanced manufacturing technology. On the one hand, CNC equipments preserve thedevelopment of modern industrial and defense industrys; On the other hand, CNCequipments have also become the entry point of strategic emerging industries. Whether acountry has high performance and high quality CNC equipments, it has become the sign ofdegree of industrialization and comprehensive strength for a country. In recent years, withthe expansion of CNC equipment market, foreign invested enterprises keep grabing the shareof the market. The development of domestic CNC machine tools facing enormous pressureand stern challenges, because the increasingly fierce competition in marketplace.In the harsh market competition, how can we keep the high performance, high precisionand high efficiency of CNC machine tools in a long time, in other words raise thecreditability level of CNC machine tools, this has become the focus of competition ofdomestic and international market. Creditability is both the core for the quality of productand an important manifestation of the quality of product. The focus of competition for thedomestic market is also the creditability level for numerous machine tool manufacturers.Fundamental of the competition for machine tool market is the competition of the credibility.This article relies on the National Natural Science Foundation of China "The coupling modelof availability influence and analysis techniques for CNC machine tools based on life cycle ",taking domestic machining center as the research object, bases on a large number ofcredibility field data, studies on: the reliability model, maintenance model and availabilitymodel of whole machining center were established; the reliability model, maintainabilitymodel and availability model of subsystem were established; influences of subsystems ofmachining center were analyzed. At last the reliability growth measures for machining centerwere studied.The studies of this paper are as follows:The credibility modeling and evaluation for whole machining center. The research ofcredibility need base on a large number of field data, this article combined with subject,15machining centers of a series were field tested. A large number of field test data were got,adopting censored time test program. The failure data was processed using Johnson method.In the whole machine reliability modeling process, the problem of fitting the direction for thelinear regression analysis to least squares method as the core was analyzed for the first time. x fitting direction and y fitting direction were analyzed for statistical properties and MonteCarlo simulation. The parameters of whole machine reliability model were estimated afterselecting the appropriate fitting direction according to the conclusions. Location parameterof three-parameter weibull distribution was optimized, using differential evolution algorithm,taking related coefficient as objective function, programming in Matlab. Finally, reliabilityevaluation of whole machine was given. In the whole machine maintainability modelingprocess, parameters were estimated, using maximum likelihood estimates after deciding thedistribution type of maintainability model. Maintainability evaluation of whole machine wasgiven after establishing the two-parameter lognormal distribution model. In the wholemachine availability modeling process, coupling simulation analysis of the availability wasdone, using the method of combining sequential simulation and Monte Carlo simulation.This method not only reflect the idea that system state changes over time in sequentialsimulation, but also reflect the idea of random sampling in Monte Carlo simulation. Thismethod could combine reliability and maintainability into availability effectively. A moreaccurate and effective new method of reliability, maintainability and availability modelingtechnique for whole machining center, the accurate evaluation of credibility level of wholemachine was given, by credibility modeling and evaluation for whole machining center.The credibility modeling for subsystem of machining center. In the subsystem modelingprocess, there is less field test failure data, it is difficult to get the accurate results by generalmodeling approach of large sample. Therefore for the reliability models of subsystems, smallsample weibull distribution modeling method based on Bayes theory was adopted. Objectivefunction was optimized by differential evolution algorithm, thus estimation of weibulldistribution parameters were gotten. For the maintainability models of subsystems, not onlydid each subsystem has less maintenance data, but the priori information in maintainabilityof subsystem was less. In view of this situation, maintainability models of each subsystemwere established by lognormal distribution modeling approach of the small sample withoutpriori information. The availability models of subsystems were simulated, using the methodof combining sequential simulation and Monte Carlo simulation, regarding subsystems asseries system. According to the simulation results, the availability model of each subsystemwas established. The credibility model for subsystem was foundations of identifying keysubsystem in whole machine and further analysis influence of subsystem.The creditability influence analysis of subsystem machining center. In the past, thereliability influence research was on the condition that the system was non-repairable system,but actually machining center is a typical repairable system. For the first time this paper studied reliability influence, maintainability influence and availability influence forsubsystem, using Natvig influence that apply to repairable system. Based on influenceanalysis result, the subsystems which affect credibility of machining center most seriouslywere found out. In order to research on the accuracy of influence and give error range.one-sided confidence limits and two-sided confidence intervals for reliability influence,maintainability influence and availability influence were obtained, using the method ofcombining sequential simulation and Monte Carlo simulation. The result of intervalestimation verified that influence degrees are rational. Influence of subsystem research laythe foundation for targeted failure analysis and further proposing credibility growthmeasures, provide basis that improve the credibility of new product of machining center.Reliability growth of machining center. The three key subsystem of spindle box, toolmagazine and electrical system failure analysis included failure mode analysis and failurecause analysis. When do the criticality fuzzy analysis of the three key subsystems,machining center is a typical electromechanical integration product, failure modes arediverse, the relationship between failure cause, failure phenomenon and failure mechanism isnot only random but fuzzy and some complex uncertain, in other words there is manyfuzziness in criticality analysis. When fuzzy critical analysis is done in this paper, weintroduce triangle-interval type-2fuzzy membership function into fuzzy critical analysis.The triangle-interval type-2fuzzy membership function reflect the uncertainty of themembership function and make the membership more accurate. On this basis the eachfactor's degree of membership was expressed in the form of interval numbers, so that all theinformation of membership function was preserved. The result was gotten using fuzzycomprehensive evaluation of interval numbers at last. The interval numbers result of fuzzycritical analysis were prioritized, using interval number sorting method that base on TOPSISidea. Finally, found out the failure modes of high criticality. According to failure analysisresult and criticality analysis result, for spindle box, tool magazine and electrical system,propose reliability design improvement, reliability assurance measures in manufacturingassembly process, reliability assurance measures of key corollary parts and purchased parts.In this paper, after studying the reliability model and maintainability model ofmachining center, the simulation method is used of reliability and maintainability ofcoupling in availability,in order to establish the whole machine availability model. For theless failure data of machining center subsystem, the subsystem model could be more realisticand reasonable, using a small sample to research the reliability model, maintainability modeland availability model of each subsystem. According to subsystem model, calculate and interval estimate the reliability influence, maintainability influence and usability influenceby Natvig influence, and the results show that the larger influence subsystem for machine:the spindle box, tool magazine, electrical system. After the three key subsystems failureanalysis and criticality fuzzy analysis, the results show that: tool magazine disorder, spindledisorder, components damage have the higher influence for the whole machine. Finally,focus on the spindle box, tool magazine, electrical system, we put forward reliability designimprovement, reliability assurance measures in manufacturing assembly process, reliabilityassurance measures of key corollary parts and purchased parts.