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