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Somekeywordsrelatedwithreferencedatum（基准）Referencedatum(基准）Designreference(设计基准）Processreference(工艺基准）Locationelement(定位元件)Locationdatum(定位基准)DatumSuperposition(基准重合)Non-superposition(不重合)Operationaldatum(工序基准)Operationaldraft(工序图）referenceLocatereferenceOperationreferenceAssemblereferenceInspectionreferenceDesignreferenceProcessreferenceDefinedasthosepoints,linesorsurfaceswhichactasreferencestodetermineotherPoints,linesorsurfacesThereferenceindesigndrawingUsedtolocatethepositionoftheworkpieceinmachining1、roughreference2、finishreference3、auxiliaryreference4、mainreference5、assistantreferenceUsedtoinspecttheworkpieceinmachiningUsedtodeterminetherelativepositionbetweenpartsorcomponentsinassemblingThereferenceinoperationaldraftUsedinmachiningInspectionorassembling3.4Selectionofreferencedatum（基准）Areferenceisusedtodefinethepositionofpoints,linesorsurfacesontheworkpieceinrelationtoit.Itisalsocalledthepositioningreferencedatum.3.4.1ClassificationofreferencesThereferencecanbeclassifiedintotwocategoriesaccordingtotheapplicationpurpose.1DesignReference:Thereferenceusedindesignstagebydesigner2ProcessReference:Thereferenceusedinmachiningorassembling支座零件图3.4.1Classificationofreferences1DesignReference:ThereferenceusedindesignstagebydesignerQuestion:Couldyoutellwhatarethedesignreferencesinthedrawing?2Processreference(工艺基准）（1）Operationreference(工序基准）Inoperationaldraft,thepoints,linesorsurfacesthatareusedtodeterminetheoperationdimensionsorpositionsrelativetothemachinedsurfacearecalledtheoperationreference.Accordingtoitsapplicationpurpose,itcanbefurtherclassifiedinto4subcategoriesQuestion:Couldyoutellwhataretheoperationreferencesinthedrawing?3.4.1Classificationofreferences（2）locatingreference(定位基准）Thelocatingreferenceisusedtodeterminethecorrectpositionofthepoints,linesorsurfacestobemachinedontheworkpiecerelativetothemachinetool,fixtureandcuttingtool.Theprocessthatfindsthelocationiscalledpositioning.3.4.1Classificationofreferences---Processreference123456789101112131415161718Couldyoudescribethelocatingprocessoftheworkpieceinrelationwiththefixture?7图2-46组合夹具1234567891011121314151617181—加筋角铁（2）2—槽用螺栓（6）3—平键（10）4—方形支承5—定位支承6—方形支承7—平垫圈8—六角螺母（8）9—槽用螺栓10—钻套螺钉11—快换钻套12—钻模板13—圆形定位销14—工件15—方形支承16—角铁17—压紧螺钉18—基础板（3）inspectionreferenceThepoints,linesorsurfaceswhichareusedasareferencetoinspectthepositionofmachinedsurfacesarecalledtheinspectionreference.Inmostcases,thedesignreferenceisusedastheinspectionreference.3.4.1Classificationofreferences(4)AssemblingreferenceIntheprocessofassembling，thepoints,linesorsurfaceswhichareusedasareferencetodeterminethepositionofthepartsorcomponentsrelativetotheproductarecalledtheassemblingreference.Forexample,whenagearistobeinstalledonashaft,itsholeisusedastheassemblingreference.3.4.1Classificationofreferences3.4.2Selectthelocatingsurfacelocatingsurfacesthefirstdatumsurfaces(粗基准）theaccuratedatumsurfaces（精基准）theauxiliarydatumsurfaces（辅助基准）Howtoselectthepositionreferenceisoneofthemainfactorsthatdecidesthereasonabilityofprocessdesignandfixturedesign,aswellasthemachiningaccuracy,productivityandcost.alsocalledstartingdatumsurfaces,makinguseofthesurfacesexistingontherawblank.Themachinedsurfacesareusedasthedatumsurfacesinthefollowingoperations.Itistheauxiliarydatumsurfaces,forthepurposeofeasymachiningSometimesthelocatingsurfaceisspeciallyreservedontheroughcastforlocating3.4.2Selectthelocatingsurface1ThecriteriaofselectingtheaccuratedatumsurfacesWhenselectingtheaccuratedatumsurfaces,someaspects,suchasconvenience,accuracyandstabilitymustbetakenintoconsideration.Thefollowinggeneralprinciplesshouldbefollowed.（1）Principleofcoincidentlocatingsurfaces（基准重合）（2）principleoflocatingdatumsurfacesunchangeable（基准不变或统一）（3）principleofbeingdatumsurfaceswitheachotherandmachiningtimeaftertime（互为基准）（4）principleofself-datumsurface（自为基准）（5）Principleofstableandsimpleclamping（稳定、易装夹）3.4.2Selectthelocatingsurface（1）Principleofcoincidentreferencesurfaces（基准重合原则）Selecttheoperationdatumsurfaces(ordesigndatumsurface)aslocatingdatumsurfacesasbestaspossible.Itcanreducethemanufacturingerrorcausedbyinaccuratelocation.(a)(b)(c)1Thecriteriaofselectingtheaccuratedatumsurfaces3.4.2Selectthelocatingsurface（2）principleofdatumsurfacesunchanged（基准不变原则）Theadvantageofdatumsurfacesremainingunchanged:Differentoperationscanbecarriedoutusingthesamefixture.Thusitreducesthetimeandcostoffixturedesignandmanufacture,speedsuptheprocessofproductionpreparation,andreducestheproductioncost.Ifmostsurfacesusethesamegroupofdatumsurfaces,theerrorcausedbydatumsurfacestransitionwillbereduced,andthepositionaccuracyamongdifferentsurfacescanalsobeensured..1Thecriteriaofselectingtheaccuratedatumsurfaces3.4.2SelectthelocatingsurfaceOperationNo.OperationnameWorkplace1facingandcenterdrillingthetwoends,Enginelathe2CylindricalTurningEnginelathe3KeywaymillingUprightmillingmachine4CylindricalgrindingGrindingmachine5deburringClippingtableAnexampletoshowtheapplicationofprinciple2.Question:whatisselectedasthesamereferenceinaboveoperations?（2）principleofdatumsurfacesunchanged（基准不变原则）16Th