Fundamentals教学讲解课件

Fundamentalsof

ManufacturingTechnologyFundamentalsof

Manufacturing1IntroductionWhatisManufacturingTechnologyItisdefinedthatthebasicsubjectsaremechanicalproducts,includingparts,componentsandmachines,emphasizingtheoperatingprocessesandmethodsinvolvedformachiningandassembly.SignificanceofMechanicalManufacturingAMachineIndustryandItsSignificanceBManufacturingTechnologyUnitedStates,WestEurope,Japan,ChinaCNationanddefencepower

PropertyandSubjectoftheCourseItisanveryimportantfundamentalcourseinSpecialtyofMechanicalEngineering；Examinedcompulsorycourse.IntroductionWhatisManufactur2ContentsandFeaturesoftheCourseMainContentsA)Preface:developmentofthesubject,procedureoftheproduction,patternandlocationofthecomponentinmachiningB)MachiningaccuracyandcontrollingC)MachinedsurfacequalityandstipulationD)PlanningofmechanicalprocessesE)DesignofassemblyprocessproceduresE)Designprinciplesandmethodsofjigs/fixturesformachinetoolsF)Trends&developmentsinmanufacturingtechnologyContentsandFeaturesoftheC3FeaturesA)Diversityofthecontents,Essentialofconcepts,DegreeofdifficultyB)Largelybasedonpractice——perceptualknowledgeandexperienceinworkshopC)Withengineeringcharacteristics——solutionsarenotnecessarilyuniqueD)Prerequisite/preconditionKnowledgeofMetaltechnology,Workshoppractice,Interchangeabilityandtechnicalgauging,metalcuttingprinciplesandcuttingtooldesigns,Machinetools,etc.FeaturesA)Diversityoftheco4TeachingmethodsandlearningrequirementsTeachingmethodsA)Trialonthecoursewithbilinguallanguages（English-Chinese)B)DetailedandbrieflecturingC)KeepbalancebetweenthetheoryandpracticeD)RemaintheequilibriumweightofthedailystudyandexaminationLearningrequirementsA)Comeandconcentrateonthecourse,takenotesfortheessentialandmostimportantpointsB)WorkoutassignmentsandhandtheminintimeC)Askquestionsifany,donotaccumulateproblemsTeachingmethodsandlearning5Assessmentofthecourse

Itwillbesoevaluatedasyourfinalscoresofthecoursethatthecentigradeisutilizedwiththreeaspects:a)pointsontheanswersheetoftheexamination,b)dailybehavior,coveringattendance,assignments,displayduringthelectures,c)pointsforexperiments.Eachofthesethreeaspectshastheweightof70%,20%and10%,respectivelywiththelimitationofatleast40%ofthecontentsaresupposedtoworkoutinEnglish.FortheencouragementofpracticingEnglish，compensationissosetthatupto8%extrapointswillbeobtainediftherestofthecontentshavebeendoneinEnglishproperly,penaltypointsofattheoutside5%willgooff,howeverkeepingthefullpointsof100.(本课程的考核采用百分制，考核内容包括三部分：卷面成绩、平时成绩（出勤、作业、课堂表现）和实验成绩，分别以70%、20%和10%加权计入总成绩；按量计，至少应有40%的内容用英文完成，如不能用英文完成，视情有不超过5%的减分；其余部分如用英文完成可获上限为8%的加分，加分结果不能超过满分成绩。)Assessmentofthecourse6ContentChapterOneProductionprocedureandbasicnomenclatureChapterTwo

MachiningAccuracyandItsControlChapterThreeMachinedSurfaceQualityandControlChapterFourDesignofProcessPlanning

ChapterFiveDesignofAssemblyProcessingChapterSixDesignofFixturesofMachineToolsContent7ChapterOne:ProductionprocedureandbasicnomenclatureABasicconceptsProductionprocedureofmechanicalproductsProcessprocedureofmachiningBElementsofprocessprocedureofmachining1sequence工序；2installation安装；3station工位；4step工步；5pass走刀ChapterOne:Productionproce8SequenceSequence:processprocedureconsistsofseveralsequencesduringwhichtheworkeroragroupofworkersoperateontheworkorasetoftheworkscontinuouslyinthesameplace.(操作者、加工地、工作对象——人为划分，相对可变)SequenceSequence:processp9ExampleExample10InstallationInstallation:inasequenceiftheworkisrequiredtoputintopositionandclampseveraltimes,thepartofsequencedoneinonepositioningandclampingiscalledaninstallation.(确定)InstallationInstallation:ina11ExampleExample12StationStation:Inaninstallation,byusingtheindexingormovingdevicetheworkischangeditspositionrelativelytothecuttingtool.Allthetasksdonefortheworkinonemachiningpositioninaninstallationistermedasthestation.(确定)StationStation:Inaninstalla13ExampleExample14StepandpassStep：Inonestationifthesurfacecut,cuttingtool,velocity,andfeedremainunchanged,theseworkingcontentsarethoughtofasthestep.(加工表面、刀具、切削速度、进给量任一改变均为另一工步）Pass:Whenthesurfaceoftheworkiscutforanyonetime,suchtaskcarriedoutisnamedasthepass.(刀具在加工表面的每一次切削）StepandpassStep：Inonestati15Asystemthatcontainstheworktobemachined,fixturethatholdstheworkintheproperposition,cuttingtoolthatmachinestheworkdirectly,andmachinetoolthatgivesthepowerandprovidethemovementstoaccomplishtheprocessing.Inrecentyearsthegaugingandmeasuringisaddedtothesystem.

Processingsystem:Asystemthatcontainsthewor16机械加工工艺过程的基本概念机械制造工艺：各种机械的制造方法和过程的总和。机械加工工艺过程：在机械加工车间中，直接改变生产对象的形状、尺寸、相对位置与性质等，使其成为成品或半成品的过程。机械加工工艺规程规定产品或零部件制造工艺过程和操作方法等的工艺文件。机械加工工艺过程的基本概念17工序是组成工艺过程的基本单元，是指一个（或一组）工人在一台机床（或一个工作地点）对一个（或同时对几个）工件进行加工所连续完成的那一部分工艺过程。工序的主要依据是工作地点（或设备）是否变动，零件加工的工作地点变动后，即构成另一工序。区分工序是组成工艺过程的基本单元，是指一个（或一组）工人在一台18Step-shaftStep-shaft19Step-shaftStep-shaft20SequenceofoperationForsingleorsmallbatchproduction

Order1facing,centerdrillingcylindricalturning,groovingandchamferinglatheOrder2millingforroundedplainkey-seatsmillingmachineburringbench-workOrder3cylindricalgrindinggrinderForbatchorlotproductionOrder1facemilling,centerdrillingspecialmachineOrder2cylindricalturning,groovingandchamferinglatheOrder3millingforroundedplainkey-seatsmillingmachineOrder4burringbench-workOrder5cylindricalgrindinggrinderSequenceofoperationForsingl21PatternsofproductionaredeterminedbythebatchorlotRelationshipbetweenthebatchandthepatternofproductionN-programofproduction,Q-annualturnoutoftheproductn-numberofthecomponentsayear,-sharerate,-waste

rate,F-annual

working

days,A-numberofdaysforinventory,-numberofcomponentsinalotPatternsofproductionaredet22ItmaybeunderstoodlikethisThenumberofannualworkingdaysdividedbythenumberofthedaysspendingonthebatchofproduction(inventorydays)istheaveragenumberofbatchedperyear;andtheannualprogramdividedbythelatternumberistheamountoftheproductsinabatch.Itmaybeunderstoodlikethis23Oritmaybeknowninthefollowingway.Oritmaybeknowninthefoll24ProgramandBatchofproductionAProgramofproductionInaperiodofplanning,theturnoutofproductandscheduletobefulfillediscalledprogram.(计划期的产量加进度=生产纲领）Theturnoutinoneyearplanningisnamedtheannualprogram.BBatchofproductionAtatime,thenumberofidenticalproductstobeputintoproductionortobeproducedistermedasbatchofproduction.(一次投入生产的同一产品的数量=生产批量）ProgramandBatchofproductio25Table1-5Technologicalfeaturesinvariousproductionstyles/patternsstylecontentSingle/SmallbatchMedialbatchLargebatch/MassproductionProduct/workBlank/allowanceMachine/layoutFixtureTool/gaugeInstallationofworkAssemblingmethodLaborskillProductivityCostTechnologicaldocument/filefrequentchangeManualmold,freeforgeLowaccuracy,largemarginAll-purpose,ingroupuniversal/compositeSpecialifneededUniversalscoring/universal/specialfixtureifneededscrapinghighlowhighSimpleproceduresheetCyclicchangePartdie,,middleaccuracy/marginPartall-purpose,partspecialPipeline/ingroupWideuseofspecial/adjustablePartuniversal,partspecialPartuseofscoring/universal/specialfixtureAlittlescraping,interchangeMediocreMediocreMediocreSequencesheet,regulationNochangeWideuseofdie,dropforge,highaccuracy,lowmarginWideuseofspecial-purpose,Pipeline/automaticlineWideuseofefficient,specialWideuseofefficient,specialSpecial-purposeInterchangeLowHighlowDetailedregulation,sequence,operating,adjustingsheetTable1-5Technologicalfeature26Noticeshouldbepaidattentionto

Withthedevelopmentofthetechnologyandthediversityofthemarket,allthepatternsofproduction,inthatconventionalmassproductioncanhardlykeeppacetotherapidchangeofproductsandsinglepieceorsmallbatchproductionmayscarcelymeettheneedsofmassivedemand,essentiallyareheadingtoflexibleproduction.Noticeshouldbepaidattentio27FunctionofprocessplanningmechanicalmachiningAthebaseonwhichtheplan,dispatch,operationoftheworkersandqualitymeasuringarecarriedout.Actionpertainingtothemanagementistakenaccordingtotheprocesspanning.BThisdocumentisadoptedforthepreparationofproduction,suchasthecoretechniquesanalysis,designorpurchaseofcuttingtools,fixtures,andgauges,preparationofrawmaterials,blanks,tooling.CForbatchormassproduction,theworkshopandfactorywillbebuiltorenlargedrelyingupontheprocessplanning.Thetypesandnumberofmachinetools,thelayoutandenergyforthesemachinetool,theplacethemachinetoolstakeupandoperatorsarealldeterminedwiththeprocessplanning.Functionofprocessplanningm28Processplanningformachiningoperations

:

stipulateddocumentfortechnologicalprocess(机械加工工艺规程：以工艺文件形式规定的机械加工工艺过程)

PatternsoftheprocessplanningformachiningGenerallyspeaking,theprocessplanningformachiningappearsintheformofsheetorcardwiththesamebasiccontentinthreepatterns:PatternA:sheetofprocessprocedures(工艺过程卡),averysimpleandconcisedocument,usuallyforsingle/smallbatchproductionPatternB:sheetofprocessoperation(机械加工工艺卡),oftenforbatchproductionPatternC:sheetofprocesssequence(机械加工工序卡),withdetailedandcompletecontents,frequentlyformassiveproductionProcessplanningformachining29Rules,stepsandcontentsofprocessplanningformachiningRules:1Guarantee/safeguardtherealizationofallthetechnicalrequirementsforthedesignedcomponentinthemachinedrawing.2Pursuethelowestcostinmachiningprocessesundertheproductionprogramandtheproductionbatch,ifpossible.3Makefulluseofthepresentproductionconditionsavailable.4Improvetheconditionsandenvironmentunderwhichworkersoperate,withsafety,comfort,andwithlowworkinghardness/severity

Rules,stepsandcontentsofp30Stepsandcontentsofprocessplanningformachining:

1)Readandlearntheassemblydrawingsandcomponentdrawings（装配图和零件图）.2)Inspectorinsightintoorchecktheprocesses(technologicalmanufacturability)used,suchasthecompleteness,correctness,andcoherenceofthesize,viewing,technicalconditionsonthedrawings,aswellasthestructuralmanufacturabilityofthecomponents（零件的结构工艺性）（underthepresentprocessconditions，beingeasyinmachiningwithlowercostwhilereachingthestandardrequired)3)Makeknownandsizeuptheblank/stock（毛坯）4)Designtheroutesofmachiningprocesses（工艺路线）5)Choosethepropermachinetoolsandtoolingforeachsequence6)Decidethetechnologicalrequirements/conditions（技术要求）andgaugingmethods（测量方法）

forthemainsequences.7)Setupthemachiningallowance（余量margin）,sequentialsize(工序尺寸）,andtolerance

（公差）oftheworkpieceforeverysequenceofoperation.8)Setupthemachiningengagement（切削用量）.9)Determinethetimerate(时间定额）.10)Fillinthetechnologicaldocument（工艺文件）.Stepsandcontentsofprocess31SectionTwo:LocationandDatumoftheworkinmachiningKeypoints:ConceptsofLocating,Clamping,datums;WaysofpositioningPrincipleofLocatingAThelocationoftheworkInstallationandclamping(装夹）:concerningaboutthewaysinwhichtheworkisinstalledandclampedinthefixtureoronthemachinetool,includingtwoaspects,locating(定位)andclamping(夹紧).SectionTwo:LocationandDatu32locatingLocating:theprocedureduringwhichtheworkgainsitsproperpositioninthefixtureoronthemachinetool.Clamping:whentheworkpiecehasgaineditscorrectpositioninthefixture,itwillbesubjecttotheexternalforceswhilebeingmachined.So,toholdorkeeptheworkpieceinthecorrectpositionisdefinitelyrequired,whichiscalledclamping.locatingLocating:theprocedur33BasicmethodsoflocationandclampingoftheworkpieceinmachiningIdirectcorrecting(直接找正装夹)——single/smallbatchproduction,andinhighquality.IIlining/scrapingandcorrecting(划线找正装夹)——smallbatchandmedium-sizedbatch,complicatedcastings,androughcastings.IIIlocatingandclampingwithjigs/fixtures(夹具装夹)——usuallyforallkindsofpatternsofproduction,becauseofthesimpleoperation,easyreachofthequality,andhighproductivity.Basicmethodsoflocationand34BSix-PointLocatingPrinciplesBSix-PointLocatingPrinciple35Acuboidisincartesiancoordinatesystemwithsixdegreesoffreedom

Thesixdegreesoffreedomarethreelinearmovementsalongthethreecoordinateaxes,respectively,andthreerotationsaroundthesecoordinateaxesAcuboidisincartesiancoord36CLocatingelementsandtheirfunctionsIntheory,thelocatingpointisthegeometricpoint;inreality,itissomethingdifferentwithitsthreedimensions.Thefollowingarecommonlyusedinworkshops.Buttonlocator(支撑钉)Plug(档销)Supportingplate（支撑板）

Pin/pinlocator（长销）CLocatingelementsandtheir37LocatingelementsandtheirfunctionsButtonCutpin/rhombuspin（削边销/菱形销）Mandrel（心轴）Vblock（形块）ShortVblock（短形块）Positioningsleeve（定位套）Fixed/floatingconicpin（固定/浮动锥销）Center(顶尖（固定/浮动）)Locatingelementsandtheirfun38Complete/incompletelocatingCompletepositioning:locatingwithconstraintforallsixdegreesoffreedom.Incompletepositioning:locatingwithconstraintforlessthansixdegreesoffreedom.Under/over-positioning:thenumberofconstraintsofdegreeoffreedomislessthanthatrequired.Under-positioningoughttobeavoidedand,thesamedegreeoffreedomisconstrainedbytwoorevenmoreconstrainingpoints,suchsituationiscalledover–positioning,whichwillbeallowedoccasionally.Complete/incompletelocating39Summaryfortheworklocation1)Analyzehowmanydegreesoffreedomshouldbeconstrainedforthesurfaceoftheworktomachine.2)Fromtheviewpointofbeingsubjecttothecuttingforces,usingtheclampingdevices,andenhancingtheproductivity,ofthecomponent,whetheradditionalconstraintsareneededinincompletelocation.3)Ifthereisunder/over-locating,andsuchover-locationisallowedornot.Summaryfortheworklocation140UnderstandingthelocatingandconstrainingDirect

view:eachofthesixpointsofthelocatingelementstouchesandkeepsthetouchingofthesurfaceoftheworkpiecewithacertaincontactarea(whichmaybeextendedininfinity),boththepointandthetouchedsurfaceisrigid.Backwardview:ifthesurfaceoftheworkgoesawayfromthelocatingelement,thatistoseparatefromtheelement,itisnolocatingatall.Understandingthelocatingand41Thelocatingelements:buttonlocatorThelocatingelements:button42Buttonandpin/longpinButtonandpin/longpin43Rhombuspin,locatingcombination:longpinwithsmallshoulder,andbuttonwithlargeshoulderRhombuspin,locatingcombinat44Fixedconicpinandfloating

conicpinFixedconicpinandfloating

45Mandrel,long,short,andwithslighttaperMandrel,long,short,andwith46Vblock，Withnarrowedone,twonarrowedpieces,andwideoneVblock，Withnarrowedone,two47Locatingsleeve,withnarrowedone,withtwonarrowedpieces,andwithwideoneLocatingsleeve,withnarrowed48Center,floatingcenter,andtaperedmandrelCenter,floatingcenter,andt49Completepositioning,Incompletepositioning,Completepositioning,Incomple50Under/overpositioningUnder/overpositioning51Over-positioningOver-positioning52DDatumNotion:datumisthepoint,lineorsurfacebasedonwhichthegeometricrelation-shipsamonggeometricelementsoftheobjecttobeworkedataredetermined.Theconceptissoimportantthatismaybeusedforanyaspectofproduction,fromdesign,throughmanufacturingincludingsequencesofoperation,tothegaugingandassembly.DDatumNotion:datumi53datumDatummaybeclassifiedintotwocategories,DesigndatumandTechnologicaldatum,accordingtotheirfunctions.Idesigndatum:indesignofcomponents,theoriginfromwhich,accordingtotheassemblyrelationshipofthecomponentandtherelativerelationshipofthestructuralelementsofthecomponentitself,thedimensioningisdone.Theseoriginalpositionsfordimensioningarecalleddesigndatums.(设计图纸上零件标注的起始位置)IItechnologicaldatum:datumusedintheprocessoperationsistermedtechnologicaldatum,whichcanbeevenclassifiedas:datumDatummaybeclassifiedi54ExampleofdesigndatumExampleofdesigndatum55Technological/processdatumsSequentialdatum:

onthesequentialdrawing,datumthatisusedinthissequencetodeterminethesize,form,andpositionoftheworkafterbeingmachinedisnamedSequentialdatum.Thethreeaspectsaresupposedtobetakenintoconsideration:thepriorityofsequentialdatumispaidtothedesigndatum,thatisusethedesigndatumassequentialdatum,theselecteddatumisfavorableforthelocationandthegaugingofthework,andiftheaboverequirementsarehardlymet,thedatumoughttobeusedtoguaranteethetechnicalconditions.Technological/processdatumsSe56Locating,gauging,andassemblingdatums

Locatingdatum:datumusedfortheworkpiecetogainitsproperpositioninmachining,itdirectlyinfluencestheeffectivenessofmachining.LocatingdatumcoversRoughdatumandFinishingdatum.a)Roughdatum/Finishingdatum:un-machinedlocatingdatum,inotherword,anylocatingdatumusedinthefirstsequenceofoperationinthemanufacturingprocessplanningistheroughdatum;finishingdatum:machinedlocatingdatum.b)additional/auxiliarydatum:thespeciallydesigneddatumintheworkpiecebecauseoftherequirementofthemechanicalprocessoperations.Locating,gauging,andassembli57GaugingandassemblingdatumsGaugingdatum:duringandaftermachining,datumusedformeasuringandcheckingtheform,position,anderrorofsize,oftheworkpiece.Assemblingdatum:inassemblingdatumadoptedtodeterminetherelativepositionsoftheworkorthecomponentintheproduct.GaugingandassemblingdatumsG58MeasuringdatumMeasuringdatum59AssemblingdatumAssemblingdatum60Sectionthree:Designtheroutesofmachiningprocesses（工艺路线的制定）Considerationmustbetakenwiththelocatingdatumoftheworkpiece(定位基准）,theprocessmethods（加工方法）,theorderoftheprocesses（加工顺序）,heattreatment（热处理）,testing（检验），andtherelatedoperations（其他工序）.Aselectionoflocatingdatums(定位基准的选择)Bselectionofeconomicaccuracyandprocessmethodsofmachining（机加的经济精度与方法）Cmachiningroutesforthetypicalsurfaces（典型表面的加工路线——外圆、孔和平面）Dorderofsequences（工序顺序安排）Sectionthree:Designtherout61Fromtheexampleaboveitisknownthattheselectionoftheroughdatummayinfluencetherelationshipbetweenthemachinedandun-machinedsurfacesaswellastheallocationoftheallowance.Inaddition,theinitialroughmachiningmustencountersuchtask.Soitisinevitableandsignificanttoselecttheproperroughdatum.

Selectingrules:Iguaranteetheproperrelativepositions.IIguaranteereasonableallocationoftheallowanceforthesurfacebeingmachined.IIIfacilitatethelocatingandclampingoftheworkpiece.Forthisreason,theselectedsurfacesasthedatumsmustbetosomeextentsmooth,enough-sized,flasher-free,withoutotherdefectssuchasreservoirandriserorthelike.IVtheroughlocatingdatumusedonlyforonetime(withoutrepetition)Fromtheexampleaboveitisk62SelectionofroughdatumSelectionofroughdatum63Aselectionofroughdatum(粗基准的选择)

Aselectionofroughdatum(粗基64Non-repetitionofroughdatuminuseNon-repetitionofroughdatum65Selectionofthefinishingdatum

Forselectingthefinishingdatum,themainconcernishowtomeetthetechnicalconditionsandguaranteetheproperinstallation,reliabilityandconvenienceintheinstallation

Selectingrules:Ioverlappingprinciple(基准重合）-datumusedasthesameasdesigndatumIIunifyingprinciple（基准统一）-usethesamedatumasearlyandasfrequentlyaspossibleIIIinter-referenceprinciple（互为基准）-especiallyusedforthehighaccuracyofrelativepositionsofthesurfacesIVself-referenceprinciple（自为基准)-forsequenceofsmallroughness,smallandevenallowanceVclamping-facilitating/convenientprinciple（便于装夹）-forproperandsecure(reliable)locating,simplestructureoftheclampingdevicewitheasyoperationSelectionofthefinishingdat66Theprocessrouteandconversionofthebox-likecomponentinunificationofdatums

SequenceofFaceSideUndersideUpperPinholeLongitudinalholeTransverseholeHolesforfasteningoperationsurface

0Ra50μm1Roughandsemi-finishingUppersurfaceRa3.2μm2DrillthepinholesandholesforfasteningontheupperRa3.2μm3SideandundersideRa3.2μmRa3.2μm4faceRa3.2μm5FinishingundersideRa1.6μm6FinishinguppersurfaceRa1.6μm7RoughmachiningLholeRa12.5μm8Semi-finishingLholeRa6.3μm9finishingLholeRa3.2μm10TransverseholeAndholeforfasteningRa6.3μm11MachiningotherholesforfasteningRa6.3μmTheprocessrouteandconversi67box-likecomponentbox-likecomponent68Bselectionofeconomicaccuracyandprocessmethodsofmachining（机加的经济精度与方法）

Notion:economicaccuracyinmachiningUnderthecommonmachiningconditions,thatis,withfacilitiesandtoolinginstandardquality,theoperatorswithtypicalskills,andinratedtime,themachiningisdonewiththerelevantaccuracyandroughnessimpartedtothecomponent.SuchaccuracyandroughnessiscalledtheeconomicaccuracyinmachiningBselectionofeconomicaccura69Machiningerrorvscost,andthetrendofmachiningaccuracyMachiningerrorvscost,andt70Cmachiningroutesforthetypicalsurfaces（典型表面的加工路线——外圆、孔和平面）CylinderHoleFlat/plane/surfaceCmachiningroutesforthetyp71Dorderofsequences（工序顺序安排）

Dorderofsequences（工序顺序安排）

72Sectionthree:determinationofmachiningallowance,dimensionsbetweensequences,andtolerancemachiningallowance:thedifferencebetweenthesizeoftheblankandthatofthecomponentdesignondrawing

thetotalallowanceisequaltothesumofmaterialthicknesstoberemovedforeverystepintheprocessoperation.Sequentialallowance:thethicknessofmetalremovalofthecutlayerineverysequenceTherelationshipbetweenthetotalallowanceandSequentialallowancewillbeexpressedintermsof

Zo=Z1+Z2+…+Zn=Sectionthree:determinationo73

whereZoisthetotalmachiningallowance,

Ziisasequentialallowanceand

nisthenumberofthesequencesforacomponent.sequentialallowancecanalsobedefinedasthedifferencebetweenthetwoadjacentlynominalsequentialsizes.Fromthislightofstatement,sequentialallowancecanbeclassifiedsinglesideallowanceforasymmetricworkandbilateral/doublesideallowanceforsymmetricwork,respectively.TheyareexpressedintermsofZi=li-1-liAnd

2Zi=li-1-liWhere

Ziisthecurrentsequentialallowanceli-1isthelastprevioussequentialnominalsizeliisthecurrentsequentialnominalsize

whereZoisthetotalmachini74Single-side,bilateral/double-sideallowanceSingle-side,bilateral/double-75NotionofenvelopingobjectorenvelopedobjectfordimensioningSituation:thereisapairofmatingparts(配合运动副，如一对齿轮啮合，活动铰链),oneofwhichwithitsexternal/opensurfacefitsanotherpart,theformeroneiscalledenvelopedobjectthatiscoveredbythelatterpart,andthelatteroneiscalledenvelopingobject.ExamplesaredepictedbelowNotionofenvelopingobjector76envelopingobjectorenvelopedobjectfordimensioningenvelopingobjectorenveloped77Sequentialallowance,entering-objectdimensioning(入体方向标注)Sequentialallowance,entering78entering-objectdimensioningDiameterofHoles,widthofkeyseatsetc.arethenominaldimensionwiththeirsmallestsize;Diameterofshaft,widthofkeysetc.arethenominaldimensionwit