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外文翻译---尺寸控制.doc

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外文翻译---尺寸控制.doc

附录附录1英文翻译DimensionalControlIntheearlydaysofengineer,thematingofpartswasachievedbymachiningonepartasnearlyaspossibletotherequiredsize,machiningthematingpartnearlytosize,andthencompletingitsmachining,continuallyofferingtheotherparttoit,untilthedesiredrelationshipwasobtained.Ifitwasinconvenienttoofferoneparttotheotherpartduringmachining,thefinalworkwasdoneatthebenchbyafitter,whoscrapedthematingpartsuntilthedesiredfitwasobtained,thefitterthereforebeingafitterintheliteralsense.Itisobviousthatthetwopartswouldhavetobedonealloveragain.Inthesedays,weexpecttobeabletopurchaseareplacementforabrokenpart,andforittofunctioncorrectlywithouttheneedforscrapingandotherfittingoperations.Whenonepartcanbeusedofftheshelftoreplaceanotherofthesamedimensionandmaterialspecification,thepartsaresaidtobetobeinterchangeable.Asystemofinterchangeabilityusuallylowerstheproductioncosts,asthereisnoneedforanexpensivefiddlingoperation,anditalsobenefitsthecustomerintheeventoftheneedtoreplacewornparts.Italso,however,demandsthatthedimensionofmatingpartsbespecified,andthatdimensionalvariations,duetomachineandoperatorshortcomings,betakenintoaccount.Someformofinspectionmustbeintroducedtoensurethatthemanufactureiscontrolledthisisparticularlyimportant,becausedimensionalerrorsmaynotberevealeduntilsometimehaselapsed,andoftenmanymilesfromtheplacewherethemachiningwasdone.1.ToleranceandLimitsofsizeSinceitisacceptedthatitisvirtuallyimpossibletomanufactureapartwithouterror,orintherareeventofapartbeingwithouterror,tobeabletoproclaimittobeperfectbecausethemeasuringinstrumentsaresubjecttoerrors,itisnecessarytoindicatethemaximumerrorspermitted.Thedraughtsmanmustindicatethelargestandsmallestsizesthatthelimitsofsize,andthedifferencebetweenthemiscalledthetolerance,theactualtolerancemustbeincreasedwithsize.Thetoleranceshouldbeaslargeaspossible,tokeepthecosttoaminimum.Themethodofindicating,onadrawing,thepermittedtolerancedependsmainlyuponthetypeofoperationinvolved,butlocalpreferencemustalsobetakenintoaccount.Thefollowingexampleswillillustratesomeofthemethodsused,1Unilaterallimits.Theseareusuallyusedwhenthedistancebetweentwofaces,orthediameterofaholeorshaftidspecified.Forexample,whenadiameterisbeingground,themachinistwouldprefertoaimatthelargestsizepermitted,sothat,intheeventofhisreachingadiameterthatisjustalittlelargerthanthemaximumsizepermitted,hecantakeanothercut,knowingthathecanuseupthewholeofthetolerancebeforethejobisrejected.Adraughtsmanmightdimensionanominal750.012mmdiametershaftasD75.Similarly,anominal75mmholemightdimensionedasD750.012,thesamereasoningappliesasforshafts.2Bilaterallimits.Theseareusuallyappliedwhen,forexample,thepositionofaholeisspecified.Themachineoperatormaypositionheholenearerthedatumorfurtherfromthedatumthanintended,hemustaimbetweenthelimitsofposition,sothatthemaximumerrorcanbemadewithoutcausingtheparttoberejected.Thecenterdistancebetweentwoholeswouldthereforebespecifiedas,forexample,1000.02mm.2.Fitsareconcernedwiththerelationshipbetweentwoparts.Considerashaftandaholecombinationiftheshaftislargerthanthehole,theconditionissaidtobeofinterferenceandifsmallerthanthehole,theconditionissaidtobeofclearance.Theinterferencemaybesuchthatthetwopartscanbeassembledonlybyshrinking,oritmaybeveryslight,sothatthepartscanbeassembledbyhandoperatedpress.Similarly,theclearancecanbeslight,sothattheshaftcanrotateeasilyinthehole,orbelarge,sothatthereisampleclearanceforboltstopassthrough.Inorderthatthepreciseconditionisensured,thelimitsofsizeofboththeshaftandtheholemustbestipulated.1Classesoffit.Theseareclassifiedasfollows.Clearancefit.Whenthelimitsofsizeofboththeholeandtheshaftaresuchthattheshaftisalwayssmallerthanthehole,thefitidsaidtobeaclearancefit.Interferencefit.Whenthelimitsofsizeofboththeholeandtheshaftaresuchthattheshaftisalwayslargerthanthehole,thefitidsaidtobeainterferencefit.Transitionfit.Whenthelimitsofsizeofboththeholeandtheshaftaresuchthattheconditionmaybeclearanceorinterference,thefitidsaidtobeatransitionfit.2HolebasedsystemandShaftbasedsystem.Inordertoobtainarangeofdegreesofclearance,anddegreesofinterference,itisnecessarytouseawidevariationofholesizesandshaftsizes.Forexample,amanufacturingcompanycouldbemakinganumberofparts,allofanominal25mmdiameter,butwhichareallslightlydifferentinactuallimitsofsize,tosuittheactualfitrequiredofeachpairofparts.Thissituationcouldmeanthatalargenumberofdrills,reamers,gauges,etc.wererequired.Itislogicalthat,toreducethisnumber,astandardholecouldbeusedforeachnominalsize,andthevariationoffiteobtainedbymakingthematingshaftsmallerorlargerthanthehole.Thisisknownasaholebasedsystem.Alternatively,astandardshaftcouldbeusedforeachnominalsize,andthevariationoffitisobtainedbymakingthematingholelargerorsmaller,asrequired.Thisisknownasashaftbasedsystem.aholebasedsystemisusuallypreferred,becauseitstandardizesfixedsizeequipmentsuchasreamerandpluggaugesbutashaftbasedsystemisusuallyalsoprovided,becausesometimesitismoreconvenienttoemployacommonshafttowhichanumberofcomponentsisassembled,eachwithadifferentfit,andsometimesitisconvenienttousebarstockwithoutfurthermachining.3.SystemsoflimitsandfitsItisconvenienttoestablishastandardizedsystemoflimitsandfits,notonlytoeliminatetheneedforthedraughtsmantodeterminethelimitseachtimeanassemblyisdetailed,butalsotostandardizethetoolsandgaugesrequired.Asystemoflimitsandfitsshouldcaterforawiderangeofnominalsizes.Tosatisfythevariousneedsofindustry,andshouldcaterforawiderangeofqualityofwork.Thesystemshould,ifpossible,betabulated,tosavetheuserthetroubleofhavingtocalculatethelimitsofsizetosuitoftheclassoffit,thequalityofthework,andthesizeofthepart.4.BritishStandard45001969,ISOlimitsandfitsThisstandardreplaceBS4500isessentiallyarevisionofBS1961tobringtheBritishStandardintolinewiththelatestrecommendationsoftheInternationalOrganizationforStandardizationISO.Thesystemreferstoholesandshafts,butthesetermsdonotonlyapplytocylindricalpartsbutcanequallywellbeappliedtothespacecontainedby.Orcontaining,twoparallelfacesortangentplanes.Thesystemistabulated,andcoverssizesupto3150mm.TheNumericalControlsdevelopmentThefirstelectroniccomputerintheworldemergedin1946,thisindicatesthemankindhascreatedthetoolthatcanstrengthenandreplacethementallabourpartly.It,andmankindthosethatcreatetostrengthentoolofmanuallaborcompareamongagriculture,industrialsociety,thequalitativeleaphasarisen,hasestablishedthefoundationthatthemankindenterstheinformationintensivesociety.6yearslater,namelyin1952,thetechnologyofthecomputerwasappliedtothelathe,thefirstnumericalcontrollathehasemergedinU.S.A..Fromthenon,thetraditionallathehadproducedthechangeofthequality.Innearlyhalfacentury,thenumericalcontrolsystemwentthroughtwostagesandsixgenerationsdevelopmentThenumericalcontrollatheisregardedastheintegratedtypicalproductsofelectromechanics,playanenormousroleamongmechanicalmanufacturingindustry,solvestructurecomplicated,accurate,batchlittle,changeableprocessingproblemofpartinthemodernmachinebuildingwell,andcanstabilizetheprocessingqualityoftheproducts,improveproductionefficiencybyalargemargin.Butseenfromsituationwhichenterprisesfaceatpresent,becausethenumericalcontrollathepriceisrelativelyexpensive,ambassadorsenterprisesareunabletodowhatonewantsverymuchtodotorelativelymaketheinvestmentonceonly.Ourcountrycanyetberegardedasakindofbettergoodplantothenumericalcontroltransformationoftheordinarylatheasthelathebigcountry.Thistextproposestothedomesticenterprisescurrentsituationatpresenttheeconomicnumericalcontrolofthesimpleandeasytypetransformsthethinkinganddesignmethodfortechnicalstaffofnumericalcontrolsreference.Numericalcontroltransformationmeantoordinarylathesomepositionmakecertaintransformationgenerally,matchthenumericalcontroldevice,thusmakethelathehaveworkingabilityofnumericalcontrol,itspurposeisforimprovingmachiningaccuracyoftheoldequipmentandproductionefficiency,adapttomanyvarietyandproduction,shortrunofpart,canmakeindustrialgradecanprocessthehighqualityparttoothanlowworkeratthesametime,reduceinvestmentoftechnologicaltransformationoftheequipment,etc..Priceperformanceonalltheseforimprovingbeenforlathethan,namelylastmechanical

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