The Study Of Reliability Prediction For Reconfigurable Machine Tools

Thereliabilitypredictionistheworkforevaluatingproducts(includesystems,equipments, organs)reliabilityunderthe givensituation,whichis also calledas thereliabilityevaluation.Thereliabilitypredictionisusedtospeculatethereliabilityofthe system accordingto the components, organs and the partial systems, which is aprocess from the part to the whole, from minority to majority, from lower toupper .It is to evaluate reliability of the same products at the same conditionsthrough the regulations and parameters of using statistics analysis by the means ofthe data which are obtained from failure products and simulatingthe experiment ofreliability.Reconfigurable machine tools are the applied examples of advancedreorganized manufacturingtechnique in the equipment of machine tools, which arethe new members in the modern machine tools fields. The advantages of themodule design overcome the longer period of the tradition specialized machinetools and the closer structure of the machine tools, which are to make against otherequipments conjunctions and the spare organs recycled. Meanwhile, it possessesthe flexibility of manufacturing center and can produce at medium-small batchquantities according to the request of customer order through flexibly choosingfunction modules and quickly reorganizing of the structures and functions in thelight of the manufacturing tasks. Therefore, the competitive advantages ofreorganized machine tools in the household of machine tools are more outstanding.Researching the reliability prediction for improving the level of reliability is animportantsubjectintheR&Dandapplicationofreconfigurablemachinetools.The main purpose of the reliability prediction is to evaluate the real designproject whether satisfy the regulated reliability or not under the regulatedconditions, and to compare the varieties of design solutions that can be provided tochoose, and to identify and remove the latent reliability problems, and to beadjusted to the level regulated reliability need. Therefore, the reliabilitypredicting is a basic job in the process of overall design valuation. Predictingprocess itself cannot improve the reliability level of system directly, but its valuelies in establishment of a basic rule for a choice towards the paths of influencingreliability design. The purpose of the reliability prediction of reorganized machinetools is to evaluate the reliability of reorganized machine tools and the constitutedmodule and to assure the reliability level of the proposed designs. It acts as theassistantdesignmeanstoprovideamount-fixedbasisforthedesigndecisions.This paper takes reorganized machine tools as an object, the main research ofwhich is the reliability predicting of the reorganized machine tools. Its aim is topredict the reliability reconfigurable machine tools through establishing thereliability module and compiling the corresponding computer programs in order toprovide a amount-fixed analysis basis for reliability designing, using andmaintaining of the reorganized machine tools. The paper pays attention on theresearch of the reliability of the whole reconfigurable machine tools (system), andadequately considers the reliability of the reorganized modules and the logicrelationamongthemodules andthe influences whichareresultedinbecauseoftheoperating mistake of the assembly and operation workers. We put the physicalfailure modes of the machine tools, modules and organs to be considered into thereliability predicting models and try best to make the data real and reliable. Thispapermainlystudiedfollowingcontents:Firstofall,thefailuremodeofthereconfigurablemachinetools.The failure modes of the reorganized machine tools include three failuremodes: the module failure, the failure among the modules, the whole machine(system) failure. The module failure is the function losing caused by the failure ofthe internal modules and organs in single function modules. The burnt-outelectrical axis engineer andtheloosenconjunctionlines oftheinternal modules arethe case. The failure among the modules is the module function failure caused bythat conjunctions loosening and wearing-out among the modules. The wholemachine(system)failure is mainlythemanymodules failurecausedbytheinternalfailure of the single modules or the failure among the modules, which result in thewhole failure. Machine vibrating and failure of the controlling and processingmaterials are the case, which influence the structures and actions of severalmodulessothatmakethewholemachine(system)fail.Secondly,thereliabilitymodelofthereconfigurablemachinetool.The foundation of reliability models is the key to predict the reliability ofreconfigurable machine tools. Reliability models of machine tools are commonlyexpressed with reliability logic frame diagram, common reliability models:in-tandemmodels,parallelmodelsandmixturemodels.Inordertoavoidfunctionalredundancy of machine tools modules or composed units, reliability models ofreconfigurablemachinetoolsistreatedasin-tandemmodelinthispaper.Through the analysis of logical relation between functional modules ofreconfigurable machine tools and other functional modules, four layer reliabilityframe diagrams such as subsystem level(module level),assemblysubassemblylevel and under-subassembly level are set up and the reliability frame diagram ofunitheadisanalyzedimportantly.Thirdly,thereliabilityanalysisofthereconfigurablemachinetools.There are lots of factors that can impact reliability of reconfigurable machinetools and result in some malfunctions. The most outstanding is the parametricvariation in the process which will impact machine tools reliability. This impact isrealized by affecting longevity of processing organs (including cutter) and thedegree of reliability of reconfigurable machine tools. Process parameters includeentirecontrolledparametersandlimitedcontrolledprocessparameter.Aftergettingthe date of process parameters and analyzing stress distributing diagram ofprocessing organs (including cutter) in the manufacturing processing, we canforecast reliability degree of process organ of recombination machine tools, whichestablish the foundation for the reliability prediction of whole reconfigurablemachinetools.Fourthly, the failure tree analysis and reliability prediction of thereconfigurablemachinetools.A reconfigurable threading machine is constructed for making truck gear boxin this paper, which is made up of pedestal modules,input modules,controlmodules and power modules. Using failure tree theory, we can forecast what thefailure mode of threading machine is and where it occurs in the process ofcompleting its function, and then analyze the reason causing failure. According tological relations between top event and intermediate event and bottom event,wecan set up the failure trees of reconfigurable threading machine tools and getreliability mathematics models. Through the degree of reliability of bottomevent failure trees, it can forecast the degree of reliability of the reconfigurablethreadingmachine(system).Reliabilityofunitheadmoduleandunitheadmoduletoolingsystem(screwtool)aregivendetailedfaulttreeanalysiswithmajorspaceinthispaper.Finally,developingthesoftwareofmachinetoolsreliabilitypredictionAccording to modular design characters of reconfigurable machine tools,this software simplify reconfigurable machine into five function module seriesconnection system. Put the reconfigurable machine reliability prediction two parts:reliability prediction of the reconfigurable machine's system and components orparts'reliability prediction. Reliability prediction of the reconfigurable machine'ssystem comes from components or parts'figures of reliability. Considered theprocess parameters affect on components or parts'reliability, we often useprobability theory and statistics analyze parts'undertake force's status, and thenobtain reliabilityfigures from some relative formula.This software, the calculationof which is accurate, overcomes the calculation modes of handwork operationswhichareverycomplicated,tedious, time-consumingandnot veryaccurate.Anditimprovesthecalculationefficiencyandresultaccuracyavailably.In conclusion, this paper combines the reliability frame diagram knowledgeand failure tree analysis theory organically according to modulization structurecharacteristics of the reorganized machine tools. It make good use of the previousdata to realize the reliability predicting of the reorganized machine tools (systems)usingreliabilityapplicationsoftwarefastandaccurately.