附录1机械英语文章翻译机械英语文章翻译3.docx

附录1机械英语文章翻译机械英语文章翻译3.docx

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附录1机械英语文章翻译机械英语文章翻译3

附录1机械英语文章翻译_机械英语文章翻译3

附录1

英文翻译

DimensionalControl

Intheearlydaysofengineer,thematingofpartswasachievedbymachiningonepartasnearlyaspossibletotherequiredsize,machiningthematingpartnearlytosize,andthencompletingitsmachining,continuallyofferingtheotherparttoit,untilthedesiredrelationshipwasobtained.Ifitwasinconvenienttoofferoneparttotheotherpartduringmachining,thefinalworkwasdoneatthebenchbyafitter,whoscrapedthematingpartsuntilthedesiredfitwasobtained,thefitterthereforebeinga'fitter'intheliteralsense.Itisobviousthatthetwopartswouldhavetobedonealloveragain.Inthesedays,weexpecttobeabletopurchaseareplacementforabrokenpart,andforittofunctioncorrectlywithouttheneedforscrapingandotherfittingoperations.Whenonepartcanbeused'offtheshelf'toreplaceanotherofthesamedimensionandmaterialspecification,thepartsaresaidtobetobeinterchangeable.Asystemofinterchangeabilityusuallylowerstheproductioncosts,asthereisnoneedforanexpensive'fiddling'operation,anditalsobenefitsthecustomerintheeventoftheneedtoreplacewornparts.Italso,however,demandsthatthedimensionofmatingpartsbespecified,andthatdimensionalvariations,duetomachineandoperatorshortcomings,betakenintoaccount.Someformofinspectionmustbeintroducedtoensurethatthemanufactureiscontrolled;thisisparticularlyimportant,becausedimensionalerrorsmaynotberevealeduntilsometimehaselapsed,andoftenmanymilesfromtheplacewherethemachiningwasdone.

1.ToleranceandLimitsofsize

Sinceitisacceptedthatitisvirtuallyimpossibletomanufactureapartwithouterror,orintherareeventofapartbeingwithouterror,tobeabletoproclaimittobeperfect（becausethemeasuringinstrumentsaresubjecttoerrors）,itisnecessarytoindicatethemaximumerrorspermitted.Thedraughtsmanmustindicatethelargestandsmallestsizesthatthelimitsofsize,andthedifferencebetweenthemiscalledthetolerance,theactualtolerancemustbeincreasedwithsize.Thetoleranceshouldbeaslargeaspossible,tokeepthecosttoaminimum.Themethodofindicating,onadrawing,thepermittedtolerancedependsmainlyuponthetypeofoperationinvolved,butlocalpreferencemustalsobetakenintoaccount.Thefollowingexampleswillillustratesomeofthemethodsused,

（1）Unilaterallimits.Theseareusuallyusedwhenthedistancebetweentwofaces,orthediameterofaholeorshaftidspecified.Forexample,whenadiameterisbeingground,themachinistwouldprefertoaimatthelargestsizepermitted,sothat,intheeventofhisreachingadiameterthatisjustalittlelargerthanthemaximumsizepermitted,hecantakeanothercut,knowingthathecanuseupthewholeofthetolerancebeforethejobisrejected.Adraughtsmanmightdimensionanominal75-0.012mmdiametershaftasD75.Similarly,anominal75mmholemightdimensionedasD75-0.012,thesamereasoningappliesasforshafts.

（2）Bilaterallimits.Theseareusuallyappliedwhen,forexample,thepositionofaholeisspecified.Themachineoperatormaypositionheholenearerthedatum

orfurtherfromthedatumthanintended,hemustaimbetweenthelimitsofposition,sothatthemaximumerrorcanbemadewithoutcausingtheparttoberejected.Thecenterdistancebetweentwoholeswouldthereforebespecifiedas,forexample,100+0.02mm.

2.Fitsareconcernedwiththerelationshipbetweentwoparts.Considerashaftandaholecombination:

iftheshaftislargerthanthehole,theconditionissaidtobeofinterference;andifsmallerthanthehole,theconditionissaidtobeofclearance.Theinterferencemaybesuchthatthetwopartscanbeassembledonlybyshrinking,oritmaybeveryslight,sothatthepartscanbeassembledbyhand-operatedpress.Similarly,theclearancecanbeslight,sothattheshaftcanrotateeasilyinthehole,orbelarge,sothatthereisampleclearanceforboltstopassthrough.Inorderthatthepreciseconditionisensured,thelimitsofsizeofboththeshaftandtheholemustbestipulated.

（1）Classesoffit.Theseareclassifiedasfollows.Clearancefit.Whenthelimitsofsizeofboththeholeandtheshaftaresuchthattheshaftisalwayssmallerthanthehole,thefitidsaidtobeaclearancefit.Interferencefit.Whenthelimitsofsizeofboththeholeandtheshaftaresuchthattheshaftisalwayslargerthanthehole,thefitidsaidtobeainterferencefit.Transitionfit.Whenthelimitsofsizeofboththeholeandtheshaftaresuchthattheconditionmaybeclearanceorinterference,thefitidsaidtobeatransitionfit.

（2）Hole-basedsystemandShaft-basedsystem.Inordertoobtainarangeofdegreesofclearance,anddegreesofinterference,itisnecessarytouseawidevariationofholesizesandshaftsizes.Forexample,amanufacturingcompanycouldbemakinganumberofparts,allofanominal25-mmdiameter,butwhichareallslightlydifferentinactuallimitsofsize,tosuittheactualfitrequiredofeachpairofparts.Thissituationcouldmeanthatalargenumberofdrills,reamers,gauges,etc.wererequired.Itislogicalthat,toreducethisnumber,astandardholecouldbeusedforeachnominalsize,andthevariationoffiteobtainedbymakingthematingshaftsmallerorlargerthanthehole.Thisisknownasahole-basedsystem.Alternatively,astandardshaftcouldbeusedforeachnominalsize,andthevariationoffitisobtainedbymakingthematingholelargerorsmaller,asrequired.Thisisknownasashaft-basedsystem.ahole-basedsystemisusuallypreferred,becauseitstandardizes"fixedsize"equipmentsuchasreamerandplug

gauges;butashaft-basedsystemisusuallyalsoprovided,becausesometimesitismoreconvenienttoemployacommonshafttowhichanumberofcomponentsisassembled,eachwithadifferentfit,andsometimesitisconvenienttousebarstockwithoutfurthermachining.

3.SystemsoflimitsandfitsItisconvenienttoestablishastandardizedsystemoflimitsandfits,notonlytoeliminatetheneedforthedraughtsmantodeterminethelimitseachtimeanassemblyisdetailed,butalsotostandardizethetoolsandgaugesrequired.Asystemoflimitsandfitsshouldcaterforawiderangeofnominalsizes.Tosatisfythevariousneedsofindustry,andshouldcaterforawiderangeofqualityofwork.Thesystemshould,ifpossible,betabulated,tosavetheuserthetroubleofhavingtocalculatethelimitsofsizetosuitoftheclassoffit,

thequalityofthework,andthesizeofthepart.

4.BritishStandard4500:

1969,ISOlimitsandfits

ThisstandardreplaceBS4500isessentiallyarevisionofBS1961tobringtheBritishStandardintolinewiththelatestrecommendationsoftheInternationalOrganizationforStandardization（ISO）.Thesystemreferstoholesandshafts,butthesetermsdonotonlyapplytocylindricalpartsbutcanequallywellbeappliedtothespacecontainedby.Orcontaining,twoparallelfacesortangentplanes.Thesystemistabulated,andcoverssizesupto3150mm.

TheNumericalControl'sdevelopment

Thefirstelectroniccomputerintheworldemergedin1946,thisindicatesthemankindhascreatedthetoolthatcanstrengthenandreplacethementallabourpartly.It,andmankindthosethatcreatetostrengthentoolofmanuallaborcompareamongagriculture,industrialsociety,thequalitativeleaphasarisen,hasestablishedthefoundationthatthemankindenterstheinformation-intensivesociety.6yearslater,namelyin1952,thetechnologyofthecomputerwasappliedtothelathe,thefirstnumericalcontrollathehasemergedinU.S.A..Fromthenon,thetraditionallathehadproducedthechangeofthequality.Innearlyhalfacentury,thenumericalcontrolsystemwentthroughtwostagesandsixgenerations'developmentThenumericalcontrollatheisregardedastheintegratedtypicalproductsofelectromechanics,playanenormousroleamongmechanicalmanufacturingindustry,solvestructurecomplicated,accurate,batchlittle,changeableprocessingproblemofpartinthemodernmachine-buildingwell,andcanstabilizetheprocessingqualityoftheproducts,improveproductionefficiencybyalargemargin.Butseenfromsituationwhichenterprisesfaceatpresent,becausethenumericalcontrollathepriceisrelativelyexpensive,ambassador'senterprisesareunabletodowhatonewantsverymuchtodotorelativelymaketheinvestmentonceonly.Ourcountrycanyetberegardedasakindofbettergoodplantothenumericalcontroltransformationoftheordinarylatheasthelathebigcountry.Thistextproposestothedomesticenterprise'scurrentsituationatpresenttheeconomicnumericalcontrolofthesimpleandeasytypetransformsthethinkinganddesignmethodfortechnicalstaffofnumericalcontrol'sreference.Numericalcontroltransformationmeantoordinarylathesome

positionmakecertaintransformationgenerally,matchthenumericalcontroldevice,thusmakethelathehaveworkingabilityofnumericalcontrol,itspurposeisforimprovingmachiningaccuracyoftheoldequipmentandproductionefficiency,adapttomanyvarietyandproduction,shortrunofpart,canmakeindustrialgradecanprocessthehigh-qualityparttoothanlowworkeratthesametime,reduceinvestmentoftechnologicaltransformationoftheequipment,etc..

Priceperformanceonalltheseforimprovingbeenforlathethan,namelylastmechanicalperformanceandtheworkingabilitynothigherwithlessmoney.Sotransformordinarylatheasnumericalcontrollathewhetheroneimprovenumericalcontroleffectivewayofrate.Generallyspeaking,carryonthetran