【模具与数控专业英语】教学内容2104

UnitTwoDieDesign模具与数控专业英语2.4BlankingDie模具与数控专业英语2.4.1ShearingActioninDieCuttingOperationsBeforeasheet-metalpartismade,ablankofsuitabledimensionsisfirstremovedfromalargesheetbyshearing,thatis,thesheetiscutbysubjectingittoshearstresses,typicallyoncedevelopedbetweenapunchandadie.InthefollowingFigure2-5presentsthecutting(shearing)operations.InFigure2-5,(a)Schematicillustrationofshearingwithapunchanddie,indicatingsomeoftheprocessvariables.(b),(c)Characteristicfeaturesofapunchedholeandtheslug.Notethatthescalesofthetwofiguresaredifferent.模具与数控专业英语(a)模具与数控专业英语(b)模具与数控专业英语(c)Figure2-5Schematicillustrationofshearingwithapunchanddie模具与数控专业英语Thecuttingofmetalbetweendiecomponentsisashearingprocessinwhichthemetalisstressedinshearbetweentwocuttingedgestothepointoffracture，orbeyonditsultimatestrength．Themetalissubjectedtobothtensileandcompressivestresses,stretchingbeyondtheelasticlimitoccurs，thenplasticdeformation，reductioninarea,andfinally，fracturingstarsthroughcleavageplanesinthereducedareaandbecomescomplete．模具与数控专业英语ThefundamentalstepsinshearingorcuttingareshowninFigure2-6．Thepressureappliedbythepunchonthemetaltendstodeformitintothedieopening．Whentheelasticlimitisexceededbyfurtherloading,aportionofthemetalwillbeforcedintothedieopeningintheformofanembossedpadonthelowerfaceofthematerial．Acorrespondingdepressionresultsontheupperface,asindicatedatFigure2-6a．Astheloadisfurtherincreased，thepunchwillpenetratethemetaltoacertaindepthandforceanequalportionofmetalthicknessintothedie，asindicatedatFigure2-6b．模具与数控专业英语Thispenetrationoccursbeforefracturingstartsandreducesthecross-sectionalareaofmetalthroughwhichthecutisbeingmade．Fracturingwillstartinthereducedareaatbothupperandlowercuttingedges，asindicatedatFigure2-6c,d．Iftheclearanceissuitableforthematerialbeingcut,thesefractureswillspreadtowardeachotherandeventuallymeet，causingcompleteseparation［2］.Furthertravelofthepunchwillcarrythecutportionthroughthestockandintothedieopening．模具与数控专业英语Figure2-6Stepinshearingmetal模具与数控专业英语2.4.2CenterofPressureIfthecontourtobeblankedisirregularlyshaped，thesummationofshearingforcesononesideofthecenteroftherammaygreatlyexceedtheforcesontheotherside．Suchirregularityresultsinabendingmomentinthepressram，andundesirabledeflectionsandmisalignment.Itisthereforenecessarytofindapointaboutwhichthesummationofshearingforceswillbesymmetrical.Thispointiscalledthecenterofpressure,andisthecenterofgravityofthelinethatistheperimeteroftheblank.Itisnotthecenterofgravityofthearea.模具与数控专业英语Thepresstoolwillbedesignedsothatthecenterofpressurewillbeontheaxisofthepressramwhenthetoolismountedinthepress．模具与数控专业英语2.4.3ClearancesClearanceisthespacebetweenthematingmembersofadieset．Properclearancesbetweencuttingedgesenablethefracturestomeet．Thefracturedportionoftheshearededgewillhaveacleanappearance．ForOptimumfinishofacutedge，properclearanceisnecessaryandisafunctionofthetype，thickness，andtemperoftheworkmaterial．Clearance，penetration，andfractureareshownschematicallyinFigure2-7．模具与数控专业英语Figure2-7Punch-and-dieclearance,punchpenetrationintoandfractureofdie-cutmetal模具与数控专业英语2.4.4BlankingDieDesignThedesignofasmallblankingdieshowninFigure2-8isthesameasthatthepiercingdieofFigure2-4exceptthatadiereplacesthediebushingsandthetwopiercingpunchesarereplacedbyoneblankingpunch．Astockstopisincorporatedinsteadofnestplates.Tinsisadrop-throughdesignsincethefinishedblanksdropthroughthedie,thelowershoe，andthepressbolster．模具与数控专业英语Figure2-8Asimpleblankingdie1.guidepost,2—guidebushing,3—stockstop,4—uppershoe,5—lowershoe.模具与数控专业英语Largeblanksarecommonlyproducedbyaninvertedblankingdie（Figure2-9）inwhichthedieismountedtotheuppershoewiththepunchsecuredtothebottomshoe．Thepassingofalargeblankthroughthebolsterisoftenimpracticalbutitssizemaynecessitatesectionaldiedesign（Figure2-10）．模具与数控专业英语Figure2-9AinvertedblankingdieFigure2-10Eight-sectionlayoutfordie模具与数控专业英语Draft,orangularclearanceinaninverteddieisunnecessarybecausetheblankdoesnotpassthroughit．Foreaseofconstruction，regrinding，andstrengththecuttingedgesofeachsectionshouldnotincludepointsandintricatecontour,withstraightcontour.Sections1and2ofthedieofFigure2-10werelaidouttoincludetheentiresemicircularcontour，withstraightcontoursincludedintheothersixsections．模具与数控专业英语Thespring-loadedstripperismountedonthelowershoe；ittravelsupwardinstripperthestockfromthepunchfastenedtothelowershoe．Stripperboltsholdandguidethestripperinitstravel．Ontheupstrokeoftheram,theupperendoftheknockoutrodstrikesanarmonthepressframe,whichforcesthelowerendoftheroddownward，throughthedie，andejectsthefinishedblankfromthediecavity．Astopcollarretainstherodsandlimitstheirtravel．模具与数控专业英语2.4.5DefinitionofVariousShearingOperationsSeveraloperationsbasedontheshearingprocessareperformed.Wefirstdefinetwoterms.Inpunching,theshearedslugisdiscarded(Figure2-11a).Inblanking,theslugisthepartandtherestisscrap.Manyoftheoperationsdescribedbelowcannowbecarriedoutoncomputer-numerical-controlledmachineswithquick-changetoolholders.Suchmachinesareparticularlyusefulinmakingthoseprototypesofsheet-metalpartsthatrequiresever