三維機(jī)械設(shè)計(jì)及三維標(biāo)注英文版課件

3DMechanicalDesign

and3DAnnotationUsingUGNXTheobjectiveofthismoduleistohelpstudentstounderstandthefundamentalsofcomputer-aideddesign(CAD)conceptsandbecomefamiliarwiththeoperationsinCADmodelingsoastoeffectivelyuseCADapproachesformechanicalproductdesign.ThecommercialCADsystem,UGNXisemployedastheplatformforCADenvironment.InChapter1,thebriefintroductiontothedevelopmentprocessof3DmodelingtechniquesinCADanditsapplicationstomechanicaldesignaregiven.Followingthisintroduction,importanttopicsinproductmodelingusingUGNX,includingthebasicsofUGNX,sketch,partmodeling,assemblymodeling,drawingand3Dannotationareprovided.Teachinghours:32(10hoursforlaboratoryexercise);ModulePoint:2Reference:[1].3DMechanicalDesignand3DAnnotationUsingUGNX(UGNX三維機(jī)械設(shè)計(jì)及三維標(biāo)注)[M].北京：鐵道出版社，2019[2]CHANGKUANGHUA.ProductDesignModelingusingCAD/CAE[M].ElsevierScience,2014.Chapter1IntroductiontoCADinMechanicalEngineering車(chē)輛工程系MainpointsThischapteraimsatintroducingthedevelopmenthistoryofCADtechnologyanditsapplicationinmechanicaldesign,theadvantagesof3DmechanicaldesignandthedataexchangestandardofCAD.Themainaspectsofthischapterare:(1)MasterdevelopmentofCADtechnology;(2)Understandtheadvantagesof3Dmechanicaldesign;(3)UnderstandCADdataexchangestandards.1.1DevelopmentHistoryofCADTechnologyThefirstcomputergraphicssystemwasinventedbytheUnitedStatesinthe1950s,thenapassivecomputer-aideddesigntechniqueswithsimpleplotoutputcapabilitieswasdeveloped.Atthebeginningof1960s,surfacemodelingincomputer-aideddesign(CAD)applicationbecameareality,andcommercialcomputergraphicsequipmentwasintroducedinthemid-1960s.In1970s,acompleteCADsystembegantoform.Peoplewishedtousethistechnologytoeliminatethetraditionalmanualsketchingthatiscumbersome,time-consumingandlowindrawingaccuracy.Atthattime,thestartingpointofCADtechnologyistousethetraditionalthree-viewmethodtoexpressthepartsanduse2Dengineeringdrawingsproducedonpaperasmediafortechnicalcommunication.Thistechnologyisknownastwo-dimensional(2D)modelingtechnology.ThemeaningofCADatthistimeisonlyasubstituteforthedrawingboardFigure1-1DevelopmenthistoryofCADtechnology

1.1.1Wireframemodels

wireframemodel:Theconstructionof3Dsolidswithwireframesandpolygons.Thismodelingmethoddescribesobjectswithasetofedgesformedentirelybyverticesjustliketheframemadebythewire.1.1.1WireframemodelsAdvantages:bringsaccessibilitiesfortheproductionofengineeringdrawingssuchasasimplestructurelowrequirementsoncomputerperformancerepresentthree-dimensionaldataofbasicobjectscangeneratearbitraryviewscanmaintainacorrectprojectionrelationshipbetweenviewscangeneratetrimetricviewsandperspectiveviews1.1.1WireframemodelsDisadvantages:inconclusivefortherealityoftheobjectinawireframebecauseallthecurvesaredisplayedimpossibletorepresentthenonpolygonsurfaceduetothelackofsurfacegeometricinformationmisstherelationshipinformationbetweenedgesandfaces,facesandfacesinthedatastructure1.1.1Wireframemodelscannotconstructasolidentitycannotidentifythefaceandbodycannotdistinguishtheinsideoroutsideofasolidobjectnotabletosupportafiniteelementmeshforstructuralanalysisofaphysicalobjectotherthanbeamortrussstructures.cannoteffectivelyexpressthetopologicalrelationshipbetweengeometricdataDuetothelackofsurfaceinformationofthemodelbothCAMandCAEcan’tberealized1.1.2SurfacemodelsTheBézieralgorithmwasproposedbyPierreBézier,whichprovidedthedesignertodealwithsurfaceandcurveproblemswithacomputer.Asurfacecanbethoughtofasaninfinitelythinshellstretchedoverawireframe.Basedonthedatastructureofthewireframemodel,surfacemodelsrepresentashapebyitssurfacegeometry.Asurfacemodelincludesinformationaboutthefacesandedgesofapartandcanexpressthetopologybetweentheedgeandtheface.1.1.2SurfacemodelsInsurfacemodelwecanachieveface-to-faceintersection,rendering,surfaceareacalculation,hidingandotherfunctionsTheapplicationofthesurfacemodelindicatesthatCADtechnologyisfreedfromthethree-viewmodethatsimplyactsliketheengineeringdrawingsFirsttimethemaininformationoftheproductpartsisfullydescribedbythecomputerAsurfacemodelisgoodforvisualizingcomplexsurfacesandsupportsNCtoolpathgeneration.1.1.2SurfacemodelsThesurfacemodelcanonlyrepresentthesurfaceandboundaryoftheobjectanditcannotbecut.Thephysicalpropertiessuchasmass,centroid,andmomentofinertiaofasolidobjectrepresentedinasurfacemodelishardtodetermine,anditisdifficulttoexpresscomplexmanufacturinginformation.Additionalinformationmustbeaddedtoasurfacemodelinordertospecifyin/outandtop/bottomofthephysicalobjectthatthesurfacemodelrepresents.1.1.3SolidmodelsSolidmodelscontaininformationabouttheedges,faces,andtheinteriorofthepart.Themathematicaldescriptioncontainsinformationthatdetermineswhetheranylocationisinside,outside,orontheboundarysurface.Intermsofmathematicallyrepresentingasolidobject,twomajormodelingmethodsconstructivesolidgeometry(CSG)boundaryrepresentation(B-rep)arewidelyemployedbygeometricmodelingkernels,whicharethecoreofCADsystems.1.1.3SolidmodelsCSGapproachexpressesthesequentialprocessofmodelingB-repmodelspecifiesconnectivityinformationofvertex,edge,face,andvolumethatmustbedefinedtoconstructthesolidmodel.ThesolidmodeltheoreticallyhelpstobringtogethermodelexpressionsinCAD,CAEandCAMwhichbringsamazingconveniencetotheproductdesignthepopularapplicationofsolidmodelingtechnologymarksthesecondtechnologicalrevolution1.1.4ParametricsolidmodelParametricisatermusedtodescribeadimension’sabilitytochangetheshapeofmodelgeometryassoonasthedimensionvalueismodified.Parametricmodelingmanipulatesparameterstocontrolthegeometricshapeofasolidobjects.Parameterscomefromdimensionsin2Dprofilesinsketch,dimensionson3Dsolidfeaturesandvariablesinuser-definedequations1.1.4ParametricsolidmodelThecoreofparametricmodelingistousegeometricconstraints,engineeringequationsandrelationshipstoillustratetheshapecharacteristicsoftheproductmodel.Theparametricmodelingtechniqueisalsocalledthedimension-drivengeometrytechnology.ItbroughtthethirdtechnologicalrevolutioninthehistoryofCADdevelopment.1.1.4ParametricsolidmodelSideeffects:theusermustfollowtheintrinsicusemechanismofthesoftwaresuchasneverallowingunderconstraintandsolvinginreverseorderetc.itisdifficulttoputallthedimensionswhenthecross-sectionalshapeofthepartiscomplicatedItisdifficulttodeterminewhichdimensionalmodificationwillsatisfythedesignintentsifanunreasonableparameterisgiventocauseafeaturetointerferewithotherfeatures,achangeintopologicalrelationshipiscaused.1.1.4ParametricsolidmodelApplicationFromtheapplicationpointofview,theparameterizationsystemisparticularlysuitableforthepartsindustrywherethetechnologyisquitestableandmature.Insuchanindustry,theshapeofthepartchangeslittle,andoftenonlytheanalogdesignisusedthatistheshapeisbasicallyfixed,andonlyafewkeydimensionsneedbechangedtoobtainanewserialdesignresult.1.1.5Variationalmodelingtechnologyvariationalgeometryextended(VGX),basedonparametrictechnology.Thevariabletechnologyfurtherdistinguishesthesize“parameters”definedintheparametrictechniqueintogeometryconstraintsandsize-constraints,ratherthanconstrainingallgeometriesbysizeonlyasintheparametrictechnique.itisnaturallydesirabletoallowtheexistenceofundersize-constraintsintheinitialstagesofthedesign.1.1.5VariationalmodelingtechnologyAdvantages:Canadoptthedesignmethodofthesizeaftershape.Thecorrectnessandefficiencyofthedesigncanstillbeguaranteed.Themodelingprocessisaprocesssimilartoanengineerthinkingaboutadesigninhismind.Thedesignprocessisrelativelyfreeandrelaxed.Inadditiontothegeneralserializedpartdesign,thevariablesystemisespeciallyhandywhendoingconceptualdesign,andismoresuitableforinnovativedesignsuchasnewproductdevelopmentandoldproductremodelingdesign.thefourthtechnologicalrevolutionofCADdevelopment1.1.6DirectmodelingandsynchronousmodelingtechniquesThefeature-basedparametricmodelingsystemaddstheconceptoffeaturetreetoCSG.Thisisthekernelprincipleofpopularmainstreamfeature-based3DmechanicalCADsystemsatthistime.The

directmodelingcorehasonlyB-repinformationbutdoesn’thaveCSGinformation,becausetheorderofthemodelingisnotconsidered,sodesignerscanquicklydefineandeditgeometrybysimplyclickingonthemodelgeometryandmovingit.1.1.6DirectmodelingandsynchronousmodelingtechniquesThesynchronizationtechnologyisa3Dmodelingmethodandconstraintsolvingtechniquethatcombinesfeature-basedmodelinganddirectmodelingtoachievedimension-drivenandstretchdeformation(Stretch)ina3Denvironment.Directmodelingmethodcanretainthesolidfeatureinformationofthepartandimplementthedesignchanges.Thus,thehistory-lessmodelingandfeature-basedparametermodelingareperfectlycompatible.Synchronoustechnologyadvancesalargestepontopofexistinghistory-basedparametricmodelingtechnique.Accordingtothedesigntaskandtheproductcharacteristicsofthedesign,thedesignershoulddeterminewhatkindofmodelingmethodwillbeemployedParametricmodelingsystemthatsupportsspecificparametric,featureandhistory-basedmodelingemphasizestheintegrityandsystematicnessofthedesignensuringthatanydesignchangeswillupdateallmodels.Thiscanachievemoreadvantagesintermsofcapturingandreusingdesignintents,family-basedorplatform-drivenproductdesign.1.2ApplicationofCADTechnologyinMechanicalDesignInfluenceof3DCADtechnologyonmechanicaldesignBasicfunctionsofCADsystemCADDataexchangestandard1.2.1Influenceof3DCADtechnologyonmechanicaldesign1)improvedesignquality

Thecomprehensiveknowledgeisstoredinthecomputersystem,whichprovidesascientificbasisforproductdesign.combinethepowerofhumanbeingandcomputerstheoptimizationofcertainprocessparametersandproductstructures2)savetimeandincreaseproductivityAutomationofdesigncalculationsandmodelinggreatlyreducesdesigndevelopmenttime.TheintegrationofCAD/CAMcanshortenthecycletimethedesignefficiencycanbeincreasedby3to5times1.2.1Influenceof3DCADtechnologyonmechanicaldesign3)reducecostsbyalargemarginThehigh-speedoperationsavelaborforcegreatlyoptimizeddesignbringssavingsinrawmaterialstheproductionpreparationtimeisshortened4)allowsdesignerstofocusonmorecreativeworkratherthandoingmassivecalculationsanddrawingwork5)CAD/CAE/CAMintegrationWith3DCADtechnology,mechanicaldesigntimehasbeenreducedbynearly1/3.1.2.1Influenceof3DCADtechnologyonmechanicaldesign(1)CADtechnologyismoreinnovativethantraditionalmechanicaldesign.Traditionalmechanicaldesignfocusesonpracticalexperienceanddesignmethodsaremostlybasedonanalogydesign.UsingCADtechnologyformechanicaldesign,itcanhaveastrong3Deffectwhichcanstimulatethedesigner’sinnovativethinkinganddesignanewmorecreativeproduct.(2)CADtechnologylaysthefoundationforthemechanicaldesigninformatization.CADtechnologyfullycomputerizestheentiremechanicaldesignprocess.Thus,thedesigndefectsanddeficienciescanbefoundintimethroughthe3Ddesigntechnologybeforethespecificprocessingandmanufacturing,andcanbeimprovedintime,whichnotonlyshortensthedesigntimebutalsoimprovesthequalityofthedesign.1.2.2BasicfunctionsofCADsystemCADsystemiscomposedofsystemsoftware,supportingsoftwareandapplicationsoftware.Atleastthefollowingbasicfunctionsshouldbeincluded:(1)Geometricmodeling(2)Assemblymodeling(3)Engineeringdrawing(4)Scientificcalculationandanalysis(5)Datamanagementandexchange(6)Otherfunctions1.2.3CADDataexchangestandardWiththecontinuousdevelopment,maturityofCADtechnologyandthecontinuousimprovingofCADapplicationsinvariousindustries,CADstandardizationworkhasincreasinglyshownitsimportance.Aspartofthehigh-techstandardization,CADstandardizationoccupiesaveryimportantpositionintheCADtechnology.CADdataexchangeproblemisanimportantissuefacedbyvariousindustriesafterthewidespreadapplicationofCAD.1.2.3CADDataexchangestandardthemostcommonlyemployedneutralfilesforCADmodeltranslationsmainlyare:DXF(DataExchangeFile)IGES(InitialGraphicsExchangeSpecification)STEP(StandardforTheExchangeofProductmodeldata)applicationprotocols1.2.3CADDataexchangestandardDXFfileisanASCIItextfilewithaspecialformat.Itiseasytoreadandeasytobeprocessedbyotherprograms.TheDXFdataexchangefileiswidelyusedinAutoCAD.theDXFfileisdevelopedearlier,fromthecurrentpointofview,itcertainlyhasmanyshortcomings.Itcannotdescribethecompletegeometricmodeloftheproduct.Itisdifficulttofurtherdevelopbecauseitislessinsupportofsolidmodeltranslation.1.2.3CADDataexchangestandardIGES(InitialGraphicsExchangeSpecification)itwasadaptedandrecognizedbyAmericanNationalStandardInstituteasastandardtoolformat.IGEShasbecomeanacceptableandwidelyusedneutralformatfortranslatordevelopmentbymanyCAD/CAMsoftwarevendorsIGESisstillthedefactointernationalstandarddataexchangeformatcurrentlywidelyusedinmanycountries.ChinahasadoptedIGES3.0asthenationalrecommendationstandardsinceSeptember1993.1.2.3CADDataexchangestandardTheworkwiththeISO10303standard,informallycalledStandardfortheExchangeofProductmodeldata(STEP)wasinitiatedin1984withthegoaltostandardizeexchangeofproductdatabetweenproductlifecyclesystems.Thestandardisaverycomprehensivesetofspecifications,coveringtheentirelifecycleoftheproductsuchasdesign,analysis,manufacturing,testing,inspection,etc.ThecorrespondingstandardnumberofSTEPstandardinChinaisGB16656.1.3Mainstream3Dsoftwares1.3.1CATIA1.3.2UGNX1.3.3Pro/Cero1.3.4SolidworksChapter2BasicsofNXUGNX（referredtoasUG）：NXisaProductLifecycleManagement(PLM)softwareproducedbySiemens.ItintegratesfunctionssuchasCAD/CAE/CAMandcoversthewholeprocessfromconceptdesigntoproductproduction.Itprovidessolidmodeling,surfacemodeling,assemblymodeling,drawingsandotherfunctionscommonlyusedin3DCADsoftware.NXalsoprovidesproductvalidationfunctionssuchasmodelinteractionverification,simulationandmanufacturing. Thischapterwillintroducetheuserinterface,viewoperations,mouseoperations,layeroperationsandcoordinatesystemoperations,etc.tohelpyougetstartedonlearningandusingNX.ThemainpointsofthischapterBefamiliarwiththeuserinterfaceofNX;Understandtherelatedmethodsofviewlayout;Usageandskillsofthemodelorientationviewandrenderingstyle;Transformationmethodoftheworkingcoordinatesystem;Methodsoffileoperationandlayersetting.2.1TheUserInterfaceofNX2.1.1StartandexitNX12.0WhentheNX12.0isstarted,itsstartupinterfaceasshowninthisFigure.2.1.1StartandexitNX12.0Thestartupinterfacewilldisappearafterawhile,thentheNX12.0initialoperationinterfacewillbeshownasthisFigure.2.1.1StartandexitNX12.0IntheNX12.0initialoperationinterface,itprovidesbriefinformationaboutTemplates,Parts,Applications,Resourcebar,CommandFinder,DialogBoxes,DisplayModes,Selection,MultipleWindows,ViewManipulation,Customization,ShortcutsandHelp.ItwillbeveryhelpfulforbeginnerstocarefullyreviewtheseinformationingettingstartedwithNX.ToexitNX12.0,clicktheClosebuttonontherightsideontheTitlebarofNX12.0.2.1TheUserInterfaceofNX2.1.2UserinterfaceClicktheNewbuttontocreateanewfileintheNX12.0initialoperationinterface,orclicktheOpenbuttontoopenthemodelfile,youcanenterthemainoperationinterfaceofNX12.0.Thisfigureshowsthemainoperationinterfaceforthemodeling.2.1.2UserinterfaceThemainoperationinterfacemainlyincludesTitlebar,QuickAccesstoolbar,Ribbonbar,Resourcebar,Graphicsarea,Cuel/StatusbarandTopBorderbar(includingmenubuttons,selectionbars,viewtoolbar,andapplicationtoolbar).Amongthem,theQuickAccesstoolbarisinitiallyembeddedintheTitlebar,whichisusedtodisplayandcollectsomecommontoolsforuserstoquicklyaccessthecorrespondingcommands.2.1.2Userinterface1.Titlebar:displaysinformationsuchastheNXversion,themodulecurrentlyselectedbytheuser,thefilenameofthecurrentworkingpart,andthemodificationstatusofthecurrentworkingpart.2.Ribbonbar:displaysthecommonlyusedfunctionsofNX.Itprovidesashortcuticonbuttonformenucommands.Acommandisrepresentedbyacorrespondingicon,andaseriesoficonswithsimilarfunctionsformatoolbar.2.1.2Userinterface3.Cue/Statusbar:locatedbelowthegraphicsarea.Itismainlyusedtopromptyouforthenextactionanddisplaymessage.Thecuelinelistsguidinginformationrelatedtothefunctionyouareperforming.Whenthemouseisoveragraphicelement,thestatusbardisplaysthenameofthecurrentgraphicelement;whentheuserhasselectedsomecertaingraphicelements,thestatusbarwilldisplaythecurrentlyselectedelementnameorquantity.2.1.2Userinterface4.Resourcebar:includinguserinterfacessuchasNavigator,ReuseLibrary,History,andRolestab.Thecorrespondinguserinterfacecanbeopenedbyclickingtheiconintheresourcebar.Table2-1describesthefunctionsofthecommonbuttonontheResourcebar.2.1.2Userinterface5.Graphicsarae:displaysthemodelwithwhichyouareworkingon.Itoccupiesmostofthespaceofthescreenandisusedtodisplaytheresultoftheuseroperation.2.1TheUserInterfaceofNX2.1.3CustomizingtheuserinterfaceWhenworkingwithNX12.0,sometimesyouneedanadequatelargegraphicswindow,sometimesyouneedtoaddorremovesometoolbarsontheoperationinterface,etc.ThisinvolvestheNXinterfacecustomizationissue.Hereareafewpracticaltipsrelatedtocustomizingtheuserinterface.2.1.3Customizingtheuserinterface1.Enablefunctionareatab

Whenworkingwithsomeapplicationmodules,sometimesthefunctionareaonlyprovidesthecommontabsassociatedwiththetaskinsteadofenablingtheexistingtabs.Ifnecessary,theusercanenableoneoftheothertabsformoreefficiency.Forexample,toenabletheApplicationstabinthefunctionarea,right-clicktheemptyareaofthefunctionareaandselectthetaboptionyouwanttoenableinthepopupshortcutmenu,forexample,selecttheApplicationsoption.2.1.3Customizingtheuserinterface2.UsetheCustomizecommand

IntheToolsmenu,selecttheCustomizecommand,orright-clickanywhereontoolbarandchoosetheCustomizecommandfromtheshortcutmenu.ThesystemwillshowtheCustomizedialogbox,whichcanbeusedtocustomizethemenuandtoolbar,iconsize,screendisplay,cue/statuslinelocation,andmore.2.1.3CustomizingtheuserinterfaceForexample,intheTabs/BarstabasshowninFigureone,checkorclearthecheckboxinfrontofthetoolbartabnametoenableordisabletheselectedthetoolbar.IntheIcons/Tooltipstab,youcansettheiconsizesofsomespecifictoolbarsandsetdisplayoptionoftooltips,asshowninFiguretwo.2.1.3CustomizingtheuserinterfaceInNX12.0,ifyouwanttoaddatoolcommandtoagroupinaspecifiedtoolbaroratabofaribbon,switchtotheCommandstabintheCustomizedialogbox.SelectacategoryfromtheCategorylisttodisplayallthecommandsunderthiscategory.ThenselectthedesiredcommandintheItemslistbox,asshowninthisFigure,anddragthiscommandtothespecifiedtoolbaroratabgroupinthefunctionareatofinishitsplacement.Inaddition,theoperationofcustomizingmenuoptionsaresimilar.2.1.3Customizingtheuserinterface3.Loadroles

Rolestabdisplaysthesystemdefaultanduser-definedroletypes.Usually,theuserinterfacesettingsoftherolearesavedunderthecorrespondingrole.Theusercanloadthecorrespondinguserinterfacebyclickingthecorrespondingroletype.2.1.3Customizingtheuserinterface

WhilelearningNX,youmaywanttousealimitedsetofitstools.Youcanachievethisbychoosinganappropriaterolefromthiscategorythattailorstheuserinterface,therebyhidingthetoolsandcommandsyoudonotneedfordaytodaytasks.ClicktheRolestabontheResourcebartobrowsethesystemdefaultroles,andclickthedesiredroletoloadcorrespondingsetoftoolsasshowninthisfigure.2.2BasicOperationsofNX2.2.1Fileoperations

ThebasicoperationsoffilemanagementcommonlyusedinNX12.0mainlyincludecreatingnewfiles,openingfiles,savingfiles,closingfiles,importingandexportingfiles,andsoon.1.CreatinganewfilePressthekeyboardshortcut,orchooseFiletab>New,orclicktheNewbuttonintheQuickAccesstoolbar.TheNewdialogboxwillappearasshowninfigure.Thedialogboxprovides14tabsforcreating14typesoffiles.2.2.1Fileoperations

Here,theModeltabisusedasanexampletoshowhowtocreateamodelfile.(1)Atthistime,thestatusbardisplaysthetiminginformationof“Selectatemplateand,ifrequired,aparttoreference”.SwitchtotheModeltabandselecttheUnitsoptionfromtheUnitsdrop-downlistbox,suchasMillimeters,inchesorall.2.2.1Fileoperations(2)TypeanewnameoracceptthedefaultnameintheNametextboxoftheNewFileNameoptiongroup.ThefilenamecanusuallyconsistofEnglishlettersandArabicnumerals,butitcannotcontainChinesecharacters.SinceNXusesthesameextension(*.prt)fortypessuchasmodelanddrawing,itusuallyaddsthecorrespondingtypenametothefilenametodistinguishbetweendifferenttypesoffiles,suchas:forModeling,willadd“_model”tothefilename;forAssemblies,willadd“_asm”tothefilename;forDrawing,willadd“_dwg”tothefilename,etc.(3)Selectfolder:specifiesthedirectorywherethenewfileislocated.Youcanenteranewdirectory,orbrowseforadirectory.ThefoldernamecannotcontainChinesecharacters.2.2.1Fileoperations2.OpenafileToopenanexistingfile,pressthe,orchooseFiletab>Open,orclicktheOpenbuttonintheQuickAccesstoolbartobringuptheOpendialogboxasshowninthisfigure.Browsethedirectoryandselectthefiletoopen.Ifnecessary,setwhethertoloadthesettings.YoucanpreviewthefiletobeopenedbycheckingthePreviewcheckboxandclicktheOKbutton.2.2.1Fileoperations3.SaveandsaveasafileNXprovides5methodsforsavingfilesasshownintheTable2-2.2.2.1Fileoperations

Aftermodifyingthenewlycreatedoropenedfile,youcanselectFile>Saveorclicktheicononthetoolbartosavethefiletotheoriginaldirectory;ifyouneedtosavethecurrentfileasanotherdefinednameorsavetootherdirectories,youcanselectthemenucommandFile>SaveAs.SaveAsdialogboxisshowninthisfigure.TheusercanspecifythefilesavedirectoryinSavein,enterthenewfilenameinFilenameandspecifythefilesaveformatbyselectingtheSaveastypeoptionandthenclicktheOKbuttontosavethefile.2.2.1Fileoperations4.Closefile

Toclosethefile,chooseFile>Closeandselecttheappropriateoptiontoperformthecloseoperation.Theusercanalsoclosethecurrentwindowbyclickingthebuttonintheupperrightcornerofthegraphicswindow.Whenthewindowisclosed,thesystemwillpromptwhethertosavethemodifiedfile.2.2BasicOperationsofNX2.2.2Layeroperations

Layersaredesignedtomakeiteasierforuserstomanagedesignmodels.Layersaresimilartotransparentdrawings.Drawingobjectsonaworkinglayerislikedrawinganobjectonaspecifiedpieceoftransparentpaper.Userscanchangetheworkinglayeraccordingtothedesignstatus,andcansetlayerswhicharevisibleandwhichareinvisible.Objectscanbedisplayedorhiddenthroughlayerswithoutaffectingthespatialpositionandinterrelationshipofthemodel,andthedisplaying,editing,andstateofobjectscanbecontrolledduringcomplexmodeling.Layersareusedtostoreobjectsinafile,andworklikecontainerstocollecttheobjectsinastructuredandconsistentmanner.2.2.2Layeroperations1.LayersettingsTherearefourtypesoflayerstates,namelytheworkinglayer,theoptionallayer,thevisiblelayeronly,andinvisiblelayer,aslistedinTable2-3.InNX,layersarerepresentedanddistinguishedbylayernumbers,andlayernumberscannotbechanged.Upto256layerscanbesetineachmodelfile,whicharerepresentedbylayernumbers1to256.2.2.2LayeroperationsTosetthelayer,chooseFormat>LayerSettings,theLayerSettingsdialogboxwillappearasshowninfigure.Usethisdialogboxtosettheworkinglayer,visiblelayerandinvisiblelayers,andcandefinethecategorynameofthelayer,andsoon.2.2.2LayeroperationsInordertofacilitatethelayerselection,theShowoptioncanbeusedtocontrolthelayercategoryandnamedisplayedinthelayerlist.TheShowlistincludes4options:AllLayersmeansthatalllayersaredisplayedinthelayerlist;LayersWithObjectsmeansthatonlythelayerscontainingobjectsaredisplayedinthe