机械专业毕业设计外文翻译极限与误差.docx

机械专业毕业设计外文翻译极限与误差.docx

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机械专业毕业设计外文翻译极限与误差

英文资料

LimitsandTolerances

Thebreakageofthemachinespareparts,generallyalwaysfromthesurfacelayerbeginningof.Thefunctionoftheproduct,particularlyitscredibilityanddurable,bedecidedbythequantityofsparepartssurfacelayertoalargeextent.Purposethatstudiesthemachinetoprocessthesurfacequantitybeforcontrolthemachineprocessmediumvariouscraftfactortoprocessthesurfacequantityinfluenceofregulation,inordertomakeuseoftheseregulationstocontroltoprocesstheprocess,endattaintoimprovethesurfacequantity,theexaltationproductusethefunctionofpurpose.

Themachineprocessesthesurfacequantitytousetheinfluenceofthefunctiontothemachine

（A）Thesurfacequantitytobeartowhetthesexualinfluence

1.Roughdegreeofsurfacetobeartowhetthesexualinfluence

Ajustprocessvice-oftwocontactsurfacesofgoodfriction,thefirststageisroughonlyinthesurfaceofthepeakdepartmentcontact,theactualcontactareaismuchsmallerthantheoreticalcontactarea,incontactwitheachotherthepeakoftheunitshaveverygreatstress,toproduceactualcontactwiththesurfaceareaofplasticdeformation,deformationandpeakbetweentheDepartmentofshearfailure,causingseriouswear.

Partswearmaygenerallybedividedintothreestages,theinitialstageofwearandtear,normalwearandtearallofasuddenintensephaseofstagewear.

Partsofthesurfaceroughnessofthesurfacewearbigimpact.Ingeneralthesmallerthevalueofsurfaceroughness,wearbetter.However,surfaceroughnessvalueistoosmall,lubricantsdifficulttostore,contactbetweentheadhesive-proneelements,wearittoincrease.Therefore,thesurfaceroughnessofabestvalue,thevalueandpartsoftheworkrelatedtoincreasedworkload,theinitialwearincreased,thebestroughsurfaceisalsoincreased.

2.ColdWorkinghardeningthesurfaceofthewearresistance

ProcessingtheColdWorkhardeningthesurfaceofthefrictionsurfacelayerofmetalmicrohardnessincrease,itwillgenerallyimprovethewearresistance.ColdWorkingbutnotahigherdegreeofhardening,wearresistanceforthebetter,becausetoomuchwillleadtohardeningoftheColdWorkingexcessivelooseorganizationofmetal,evenacrackandpeelingoffthesurfaceofthemetal,declinedtowearresistance.

（B）Thesurfacequalityoftheimpactoffatiguestrength

MetalhandalternatingloadsoffatigueafterthedamageoccurredinpartsoftenChilledlayerbelowthesurfaceand,thereforepartsofthesurfacequalityoffatigueveryinfluential.

1.Surfaceroughnessontheimpactoffatiguestrength

Inalternatingload,thesurfaceroughnessoftheAu-siteeasilyleadtostressconcentration,afatiguecrack,thehigherthevalueofsurfaceroughness,surfacetracesofYuShenWen,Wenattheendoftheradiussmaller,anti-fatiguedamageattheendofthemorecapacityWorse.

2.Residualstress,fatigueColdWorkhardeningoftheimpact

Residualstressontheimpactoflargepartsfatigue.Surfacelayerofresidualstressfatiguecrackwillexpandandacceleratethefatiguedamagethesurfacelayerandtheresidualstresscanpreventfatiguecrackgrowth,delayingtheformationoffatiguedamage.

（C）Thesurfacequalityofthecorrosionresistanceoftheimpact

Partsofthecorrosionresistancetoalargeextentdependsonthesurfaceroughness.Thehigherthevalueofsurfaceroughness,AuValleyaccumulateonthemorecorrosivesubstances.Corrosionresistanceofthemoreworse.

Surfacelayerofresidualstresswillproducestresscorrosioncracking,lowerpartsofthewear-resistance,andtheresidualstressistopreventstresscorrosioncracking.

（D）Thesurfacequalitywithquality

Roughsurfacewillaffectthevalueofthesizeoftheco-ordinationwiththesurfacequality.Thegapwithroughvaluewillincreasewearandtear,increasedspace,withtherequirementsofthedestructionofnature.ForFit,theassemblypartoftheprocessofconvexsurface-crowdedpeaktimes,theactualreductionofthesurplusandreducethesupportoftheconnectionbetweenthestrength.

Dimensioning

Thedesignofamachineincludesmanyfactorsotherthanthoseofdeterminingtheloadsandstressesandselectingthepropermaterials.Beforeconstructionormanufacturecanbegin,itisnecessarytohavecompleteassemblyanddetaildrawingstoconveyallnecessaryinformationtotheshopmen.Thedesignerfrequentlyiscalledupontocheckthedrawingsbeforetheyaresenttotheshop.Muchexperienceandfamiliaritywithmanufacturingprocessesareneededbeforeonecanbecomeconversantwithallphasesofproductiondrawings.

Drawingsshouldbecarefullycheckedtoseethatthedimensioningisdoneinamannerthatwillbemostconvenientandunderstandabletotheproductiondepartments.Itisobviousthatadrawingshouldbemadeinsuchawaythatithasoneandonlyoneinterpretation.Inparticular,shoppersonnelshouldnotberequiredtomaketrigonometricorotherinvolvedcalculationsbeforetheproductionmachinescanbesetup.

Dimensioningisaninvolvedsubjectandlongexperienceisrequiredforitsmastery.

Tolerancesmustbeplacedonthedimensionsofadrawingtolimitthepermissiblevariationsinsizebecauseitisimpossibletomanufactureapartexactlytoagivendimension.Althoughsmalltolerancesgivehigherqualityworkandabetteroperatingmechanism,thecostofmanufactureincreasesrapidlyasthetolerancesarereduced,asindicatedbythetypicalcurveofFig14.1.Itisthereforeimportantthatthetolerancesbespecifiedatthelargestvaluesthattheoperatingorfunctionalconsiderationspermit.

Tolerancesmaybeeitherunilateralorbilateral.Inunilateraldimensioning,onetoleranceiszero,andallthevariationsaregivenbytheothertolerance.Inbilateraldimensioning,ameandimensionisusedwhichextendstothemidpointofthetolerancezonewithequalplusandminusvariationsextendingeachwayfromthisdimension.

Thedevelopmentofproductionprocessesforlarge-volumemanufactureatlowcosthasbeenlargelydependentuponinterchangeabilityofcomponentparts.Thusthedesignermustdetermineboththepropertolerancesfortheindividualparts,Themannerofplacingtolerancesondrawingsdependssomewhatonthekindofproductortypeofmanufacturingprocess.Ifthetoleranceonadimensionisnotspecificallystated,thedrawingshouldcontainablanketnotewhichgivesthevalueofthetoleranceforsuchdimensions.However,somecompaniesdonotuseblanketnotesonthesuppositionthatifeachdimensionisconsideredindividually,widertolerancethanthosecalledforinthenotecouldprobablybespecified.Inanyeventitisveryimportantthatadrawingbefreefromambiguitiesandbesubjectonlytoasingleinterpretation.

DimensionandTolerance

Indimensioningadrawing,thenumbersplacedinthedimensionlinesrepresentdimensionthatareonlyapproximateanddonotrepresentanydegreeofaccuracyunlesssostatedbythedesigner.

Tospecifyadegreeofaccuracy,itisnecessarytoaddtolerancefigurestothedimension.Toleranceistheamountofvariationpermittedinthepartorthetotalvariationallowedinagivendimension.Ashaftmighthaveanominalsizeof2.5in.（63.5mm）,butforpracticalreasonsthisfigurecouldnotbemaintainedinmanufacturingwithoutgreatcost.Hence,acertaintolerancewouldbeaddedand,ifavariationof±0.003in.（±0.08mm）couldbepermitted,thedimensionwouldbestated2.500±0.003（63.5±0.008mm）.

Dimensionsgivenclosetolerancesmeanthatthepartmustfitproperlywithsomeotherpart.Bothmustbegiventolerancesinkeepingwiththeallowancedesired,themanufacturingprocessesavailable,andtheminimumcostofproductionandassemblythatwillmaximizeprofit.Generallyspeaking,thecostofapartgoesupasthetoleranceisdecreased.Ifaparthasseveralormoresurfacestobemachined,thecostcanbeexcessivewhenlittledeviationisallowedfromthenominalsize.

Allowance,whichissometimesconfusedwithtolerance,hasanaltogetherdifferentmeaning.

Itistheminimumclearancespaceintendedbetweenmatingpartsandrepresentstheconditionoftightestpermissiblefit.Ifashaft,size1.498

istofitaholeofsize1.500

theminimumsizeholeis1.500andthemaximumsizeshaftis1.498.Thustheallowanceis0.002andthemaximumclearanceis0.008asbasedontheminimumshaftsizeandmaximumholedimension.

Tolerancesmaybeeitherunilateralorbilateral.Unilateraltolerancemeansthatanyvariationismadeinonlyonedirectionfromthenominalorbasicdimension.Referringtothepreviousexample,theholeisdimensioned1.500

whichrepresentsaunilateraltolerance.Ifthedimensionsweregivenas1.500±0.003,thetolerancewouldbebilateral;thatis,itwouldvarybothoverandunderthenominaldimension.Theunilateralsystempermitschangingthetolerancewhilestillretainingthesameallowanceortypeoffit.Withthebilateralsystem,thisisnotpossiblewithoutalsochangingthenominalsizedimensionofoneorbothofthetwomatingparts.Inmassproduction,wherematingpartsmustbeinterchangeable,unilateraltolerancesarecustomary.Tohaveaninterferenceorforefitbetweenmatingparts,thetolerancesmustbesuchastocreateazeroornegativeallowance.

TolerancesLimitsandFits

Thedrawingmustbeatrueandcompletestatementofthedesigner’sexpressedinsuchawaythatthepartisconvenienttomanufacture.Everydimensionnecessarytodefinetheproductmustbestatedonceandrepeatedindifferentviews.Dimensionsrelatingtooneparticularfeature,suchasthepositionandsizeofhole,wherepossible,appearonthesameview.

Thereshoul