CAEDSMouldDesign

Ejectorpinsandsleeves1

EjectorpinsandsleevesSchoolofTechnologyandManagement,PolytechnicInstituteofLeiria

At themostbasic level,mouldsconsistof twomainparts: thecavityandcore.Thecoreformsthemaininternalsurfacesofthepart.Thecavityformsthemajorexternalsurfaces.Typically,thecoreandcavityseparateasthemouldopens,sothatthepartcan be removed. This mould separation occurs along the interface known as thepartingline.Thepartinglinecanlieinoneplanecorrespondingtoamajorgeometricfeaturesuchas thepart top,bottomorcenterline,or itcanbesteppedorangled toaccommodate irregular part features.Choose the partingline location tominimizeundercutsthatwouldhinderorpreventeasypartremoval.Undercutsthatcannotbeavoided via reasonable adjustments in the parting line require mechanisms (SlideMechanisms)inthemouldtodisengagetheundercutpriortoejection.

Themouldbasecomprises themajorityof thebulkofan injectionmould.Standardofftheshelf mould bases are available for most moulding needs. Typical mouldsbases are outfittedwith a locating ring and provisions for a sprue bushing in thestationaryhalf(cavity)ofthemouldandanejectorassemblyinthemovinghalf.Bothhalves comewith clamp slots to affix themould in thepress.Themovinghalfhasholes toaccommodatebars thatconnect thepressejectionmechanism to theejectorplateinthemould.Leaderpins(guidepins)projectingfromcornersofthestationaryhalfalignthemouldhalves.Returnpinsconnectedtotheejectorplatecornersprojectfrom themould facewhen theejectionmechanism is in the forward (eject)position.Asthemouldcloses,thereturnpinsretracttheejectorplate(ifnotretractedalready)inpreparationforthenextcycle.

When plastics products and their respective moulds are designed, the location ofejectors is important toensureproper stripping from the core.By selecting suitableejectorcomponents thevisualappearanceof theproductscanbeconsiderably influenced, but it is even more important that the mould performance becomes morereliableandproductionimproves.UsuallyejectorsarestandardpartsincludedintheCADStandardElementsSoftware(CADLibrary).Thoseitemsalreadysuitablecanbeselectedeasilyduringtheproductdesignstage.

Thisdocument is focusedon thedesign,material,assemblingandoperationofejectionsystems.

Introduction

CAEDSMouldDesign

Ejectorpinsandsleeves2

Typically, moulds have ejector systems built into the moving half (see followingfigure).Ejectortravelmustbesufficienttoclearthemouldingfromfixedmembersinthemould.Undercuts or pickup ribsmay bemachined intomouldmembers toinsurethatthemouldedpartremainsontheejectionsideofthemould.Pickupsizesaredeterminedforthetypeofthematerialbeingused.Partsmayberemovedfromamouldusingthecommontypeofejectororknockoutsystem.Ejectorsactuatedbyanejectorbarmustcontainpushbacksorsafetyreturnpinstorepositiontheejectorpinspriortothestartoftheinjectionormouldfillingcycle.

Figure1 Componentsofastandardtwoplatemouldbaseejectionsystemsmountedonstatichalfofthemould

The ejection unit of the moulding press activates these systems. Rods linking thepressejectormechanismtoanejectorplateinthemouldenablethepresscontrollertocontrolthetiming,speed,andlengthoftheejectionstroke.Reverseinjectionmouldsejectpartsfromthestationarysideofthemouldviaindependentejectionmechanismsoperatedbyspringsorhydrauliccylinders.Thisconfigurationfacilitatesdirect injectionontotheinsideorbacksurfaceofcosmeticparts.Theaddedcomplexityofreverseinjectionmoulds adds to themould cost. Specialized ejection components, such asknockout (KO) pins,KO sleeves, or stripper plates, project from themould ejectorplatetothepartsurfacewheretheypushthepartoutofthemould.

Manyfactorsdeterminetheamountofejectorareaneeded,includingthepartgeometry,mouldfinish,materialreleasecharacteristics,andparttemperatureatthetimeofejection.Topreventdamageduringejection,thinwalledpartsgenerallyrequirelargerejectorsandgreaterejectorareathancomparablepartswiththickerwalls.

Drawpolishing themould steel in thedirectionofejectiongenerallyhelpsejection.Thermoplasticpolyurethanes,exceptions to this rule,usuallyejectmoreeasily frommouldswithfrostedfinishesthatlimitplastictometalcontacttopeaksinthemouldtexture.

Ejectionsystems

CAEDSMouldDesign

Ejectorpinsandsleeves3

Careful consideration is essential to decisions concerning the number and area ofejectors tobeusedand the typeof system tobe employed for thevarious typesofmaterials. Itmustbeunderstood that, inmost cases, thepartbeing ejectedmay, tosomedegree,besoftduetothehightemperatureattimeofejection.Forlowestcost,mouldingpartsareejectedwhentheyare justsufficientlyhardtopreventdistortionandinmanycases,themoulditselfisheatedtoachievemaximumfeasibletemperatureatejection.The following figure illustratesdesirableknockoutpin locations forsoftmaterialssuchaspolyethylene.

Figure2 Knockoutpinlocations.Basedoncalculationtogiveminimumbendingshadedareasarepreferableejectorpinlocationsforsoftflexibleplastics.

Ejectionmarksmaybestyledintothepartwhendesirablebyaddingdesignconfiguration in these areas. This is accomplished by decorating or adding a series ofconcentricringsontheejectorpinsurface.

A summaryof standardised ejectorpins and sleeves is shown in the table onnextpage.Theyareavailable in twosteelgrades: (1) toolsteel, throughhardenedwithahardnessof ~60HRc, and (2)hotwork steel,with a core strengthof ~45HRc and anitridedsurfaceof~950HV0.3.Allejectorsmadeoftoolsteelhaveabrightappearanceontheshaft,andonlytheforgedheadisdark,fromtheannealingtreatment.Dependingonthenitridingtreatment,thepinsurfacelookseitherbrightordullgray.Ejectorsthatundergothebathnitridingprocess(Tenifertreatment)showthetypicaldullgraysurface.Forcertainapplications,e.g.,indiecastingmolds,thistypeofsurfaceismostsuitable,becausethe lubricatingfilmadheresbettertothesurface.Gasnitridedejectorshaveabrightsurfacebecauseregrindingisrequiredafternitriding.Insomecasesthesepinsare subsequently treatedbya special sulfatingprocess toobtainavisualappearancesimilartothatofbathnitridedpins.Plasmanitridedejectorsalsohaveabrightsurface,but thesamemechanicalpropertiesapplyas forTenifertreatedejectors.Becauseacertainamountofwearonejectorscanneverbeavoided, foranewmoldthedesignershouldconsiderselectingarelativelysmallerpindiameter.Ifworn,thispincanthenbereplacedbya largerone.Forthispurposethesuppliersofstandardsofferoversizeejectors.Remachiningofnitridedpinsandsleeves in the radialdirectionisnotrecommended,becausethiswouldremovethe~0.1mmthicknitridedlayer.Repeatingthenitridingtreatmentisnotadvisable.

Ejectorpins

Square partCircularpart Rectangular part

CAEDSMouldDesign

Ejectorpinsandsleeves4

Ejectorsleevesareofexcellenthelp inejectingcomplexareasofmouldingswithouttheneedtoreinforcetheproductwithspecialbossesorribs.Theyareavailableinthesame steel grades as ejectorpins. For special applications, stepped sleeves are alsoavailable as standards. For long ejectors, extension rods (Figure) can be applied toprovidestability to thinpinsandsleeves.They fitstandardejectorcomponentsandeliminatetheneedforexpensivecustommadeoversizeitems.

Figure3 Extensionforinjectorpinsandsleeves:1)screwcap;2)extension;3)lookingtab;4)groove;5)ejectorsleeve

Onthebasisofresistancetobuckling,acertainmaximumdiametertolengthratiohasbeenestablished forallejectors; therefore,suitableejectorpinswithsmalldiametersforlargemouldsarenotavailable.Whenextensionrodsareused,andwhenejectorsareworn,only the standard ejector,which ismounted to the sturdy rod (2)withascrew cap (1), needs to be replaced.A locking tab (3) pressed into the groove (4)preventslooseningofthescrewcap(1).Forusewithejectorsleeves(5),theextensionmustbedrilledthroughtosuitthecorepindiameterd.Ineverycase,theboreinthescrewcapmustbemachinedtosuittheshaftdiameterdofthepinorsleeve.

Forspecialejectionapplicationsunderthinribsorextremelynarrowcontours,bladeejectorsareavailable.

CAEDSMouldDesign

Table1. Summaryofstandardejectorpinsandsleeves

Drawing

2D 3D

DesignationStandard

Material Hardness

HotWorkSteel1.2343

Nitrided950HV0.3Corestrength1400n/mm2

EjectorpinwithcylindricalheadDIN1530AISO6751

Toolsteel1.2516

Throughhardened602HRc

HotWorkSteel1.2343

Nitrided950HV0.3Corestrength1400n/mm2

ShoulderedejectorpinwithcylindricalheadDIN1530CISO8694

Toolsteel1.2516

Throughhardened602HRc

HotWorkSteel1.2343

Nitrided950HV0.3Corestrength1400n/mm2

EjectorpinwithconicalheadDIN1530D Toolsteel

1.2516Throughhardened602HRc

HotWorkSteel1.2343

Nitrided950HV0.3Corestrength1400n/mm2

BladeejectorDIN1530FISO8693

Toolsteel Through

Ejectorpinsdesignandmaterial

Ejectorpinsandsleeves5

1.2516 hardened602HRc

HotWorkSteel1.2343

Nitrided950HV0.3Corestrength1400n/mm2

EjectorsleeveDIN16756ISO8405

Toolsteel1.2516

Throughhardened602HRc

CAEDSMouldDesign

Ejectorpinsandsleeves6

Figure4 Specialbladeejectorexample:1)ejectorblade;2)guidebushing;3)guideshellhalves;4)splitguide

Thevery thinejectorblade (1) is solidlyheldby theguidebushing (2)and is supported along its entire length by the guide shell halves (3). This design preventsbucklingandensuresreliableejection.Tofacilitateassembly,asplitguidebushingisavailable,whichcanbemountedinaborejustbelowthecavity.Difficultmachiningofthebladeslotthroughthecavityblockcanthusbeeliminated.

Figure5 Assemblyexampleofejectorpins.

Undercuts, part features that prevent straight ejection at the parting line, tend toincreasemouldcomplexityand lead tohighermouldconstructionandmaintenancecosts.Wheneverfeasible,redesigntheparttoavoidundercuts.

Minorpartdesignchangescanofteneliminateproblematicundercuts in themould.Forexample,adding throughholes cangiveaccess to theundersideof features thatwould otherwise be undercuts.Undercut features that cannot be avoided throughredesign require mechanisms in the mould to facilitate ejection. These types ofmechanisms include sideaction slides, lifter rails, jigglerpins, collapsible coresandunscrewingmechanisms.Theremainderofthissectiondiscussestheseoptions.

Sideactionslidesusecampinsorhydraulic (orpneumatic)cylinders toretractportionsofthemouldpriortoejection.Campindrivenslidesretractasthemouldopens(see following figure).As themould closes, the campins return the slides to theiroriginalpositionforthenextinjectioncycle.Slidesdrivenbyhydraulicorpneumaticcylinderscanactivateatanytimeduringthemouldingcycle,anadvantageinapplicationsrequiringtheslidestoactuatepriortomouldopeningorclosing.

Ejectionmovement

Mouldingandejectingpartswithundercutsslidemechanisms

CAEDSMouldDesign

Ejectorpinsandsleeves7

Figure6 Slidemechanisms:a)andb)motionactivatedbyguidedpillarsc)motionactivatedbynoncirculargeometriesd)e)motionactivatedbyspringsf)interiorslidemechanismg)motionactivatedbyhydraulicorpneumaticsystems.

Shallowundercutscanoftenbeformedbyspringloadedliftersorlifterrailsattachedto the ejector system. These liftersmovewith the part on an angle duringmouldopening (see following figurea)orejectionuntil the lifterclears theundercut in thepart.Avariationon this idea, the jigglerpin (see following figure b),has angledsurfacestoguidethepinawayfromtheundercutduringejection,thenreturnittothemouldingpositionastheejectorsystemretracts.

Figure7 Lifterrailsattachedtotheejectorsystem:a)angledlifters;b)lifterrailwithangledsurfaces.

Slidemechanisms

a) b) c) d)

e) f) g)

Lifterrails

Afterejection

Beforeejection

BeforeejectionAfterejection

a) b)

CAEDSMouldDesign

Ejectorpinsandsleeves8

Figure8 Realexampleoflifterrailsattachedtotheejectorsystem:a)angledlifters;b)lifterrailwithangledsurfaces.(CourtesyofaPortuguesemouldmakingcompany)

Featuressuchasinternalthreads,dimples,slots,orgroovesontheinsideofholesorcapsmayrequirecollapsiblecores.

Figure9 Plasticfeaturesthatmayrequirecollapsiblecores.

These complex cores aremade in segments that collapse toward the centre as theyretractduringmould opening (see following figure). As soon as the inner core isretracted, the segmentsmove inward, thereby releasing the product. Setting up ofmoulds is easy, because adjusting the collapsible cores isdoneduringmould constructionandmountingofadditionaldevicesisnotrequired.Thecollapsiblecoresarehardenedandreadytouse,exceptforthegrindingoftherequiredthreadsorundercuts.

LifterrailsExampleCollapsiblecores

a) b)

CAEDSMouldDesign

Ejectorpinsandsleeves9

Beforeejection

Figure10 Collapsiblecoresforexternalmouldingofpartsurfaces.

Figure11 Collapsiblecoresforinteriormouldingofpartsurfaces:a)schemeofassemblingandoperationofananteriorcollapsiblecore;b)collapsiblecore.

Expanded Collapsed

a)

b)

Cavity

CoreplatealignmentEjectionplate

b)a)

Afterejection

Beforeejection

Afterejection

CAEDSMouldDesign

Ejectorpinsandsleeves10

Smallsizecoresaresuppliedwithsegmentsseparatedfromeachotherbyfixedribs.Consequently,undercutsonthemoulding,e.g.,threads,alsoshowaninterruptiononthecircumference.Duringejectiontheremightbeadangerthatproductswillsticktothecore,anditissuggestedthatanairblowoffbeused;inaddition,infraredsafetydevicesorweightcheckscalescanensurethatallproductshavebeenejected.Available in avariety of standard sizes fromvariousmouldcomponent suppliers, thesespecialty cores are typicallymodified to produce the desired undercut shape. Thenumber and complexity of individual core components limit theminimum size ofcollapsible cores.Collapsible coresare rarelyused for insidediameters less than16mm.

Using the same operation principle of both, lifters and collapsible cores, with theflexiblecoreconceptsmallundercutscanbeeasilyreleased.

Figure12 Flexiblecores:a)operating;b)examplesofseveraldifferentgeometries

Forproductswithinternalthreads,specialconsiderationsarerequiredwhendesigning the unscrewingmechanism.A variety of devices can drive the rotation of thethreaded cores, including rackandpiniondevices actuated bymouldopening (followingfigurea),motors,orhydrauliccylinders(followingfiguresbandc);ormotordrivengearandchainmechanisms.

Flexiblecores

a) b)

Unscrewingmechanisms

CAEDSMouldDesign

Ejectorpinsandsleeves11

Figure13 Applicationofunscrewingdrivecomponents:a)activationcomponentsusinghydraulicor,pneumaticactivatedpistons;b)activationofrotationusingthemouldmovement;c)actuationofrotationusingthehydraulicmachineejector.

Themoulddesignshouldincludeprovisionstolubricatethevariousmovingpartsoftheunscrewingmechanism.Slides, cams, collapsible cores, andunscrewingmechanismsaddtothecostandcomplexityofthemould,aswellasthemouldmaintenancecost. It would be of advantage to integrate the unscrewing drive into the mould,wheretherotationisinitiatedbyaleadscrewdrivenbythemouldopeningmotion.

Whenthemouldisinstalled,onlyaspecifiedopeningstrokeneedstobeset;therefore,suchunscrewingmouldsarealsoverysuitableforautomaticmouldchanging.

Activatedbypiston

a)

b)

c)

CAEDSMouldDesign

Ejectorpinsandsleeves12

Insome injectedparts theejectionmustbedoneusing,acceleratedejectorpins.Thepplicationof these systems turnspossible,both the ejectionof someundercut fea

andtheejectioninoneorientateddirection.

followingfiguresshowstandardssystemsthathaveaveryeasyoperation.Internally the system has a rack and rotates the wheel that gives an advance to theextractorpinassembled(followingfigurea).Theaccelerationofthecentralejectorpinisusefulinordertopreventhangingoftheinjectedpartintheejectorpins.Theapplicationof thesekindsof systems canavoid the interventionofahumanor robot to

eatures

The

removethepartfromthemould.

a)

b)

c)

Acc leratedejectorpins

CAEDSMouldDesign

Figure14 Standardejectionaccelerators(onleft)andexampleofapplicationandperation(onright)

he following figureshowsasystemforacceleratingejectiondevelopedbyaPortuuesemouldmakingcompany.

Figure15 Customisedsystemforacceleratingtheejection.

Thereleaseoflargeboxtypeshapesorsimilarproductsissubstantiallyassistedwiththeuseofairpoppetvalvesorejectionpinspressurizedwithair..Ejectiondifficultiescanarise ifavacuum formsbetween thepartandmouldduringejection.Typically,thisdifficultydevelopsindeeplycored,closedbottomparts.Mouldcomponentssuchasairpoppetvalves(seefigure)canalleviatetheproblems.Airpoppetvalvesrelievethevacuumanddeliverpressurizedairbetween thepartandmouldsurfaceduringejection.Theairpoppetvalves arebuilt into the coresof the injectionmoulds.Thespringloadedconicalseatispushedforwardbytheapplicationofcompressedairatthesame timeasejectionstarts. Insomecases it isevensufficient for thepoppet toopenby itselfduringejection tobreak thevacuum.Airpoppetvalvesaremountedithpressfitintothemoldingsurface.Tofacilitatemachining,auxiliarytoolssuchasounter bores and reamers are available. Appropriate devices and fittings for air

Airassistedejection

o

Tg

d)wcEjectorpinsandsleeves13

supplyareofferedbythesuppliersofthesestandardcomponents.

CAEDSMouldDesign

Ejectorpinsandsleeves14

Figure16 Ejectionsystemsassistedbyairpressure:a)Airpuppetvalves(left)andoperation(right);b)Ejectionpinsassistedbyairpressure(left)andoperation(right);c)exampleofamouldwithanairpuppetvalve.

c)

b)

a)

Airpressure

CAEDSMouldDesign

Ejectorpinsandsleeves15

Designsrequiringthinwallsorareaswhichhaveundercutsontheinteriorrequireoneta

turedesignand the second stage to remove thepart from themould.Thisouble system permits the part to be freely ejected from the mould. This designaybeused for allmaterials. It is illustrated by the following figures.The ejection

of the machine is automatically subdivided into two stepless adjustabletrok performed with either the hydraulic machine ejectorr/and,incaseofmechanicaloperation,thereturnpinsofthemould.

igure17 le(right).

stage ejection can be supported by the application of latchesdevices (see lastgure) however, latches are often used on injectionmoldswith twomold partingvels.Atleasttwolatchassembliesaresymmetricallymounted ofthe

Duringmouldopening,onepartinglevelopensfirst;aftertravelingapredermined distance, the locking mechanism of the latch is released and the secondarting levelopens.Thiskindofstandard latchpuller isusedpreferablywiththreetemoldsinwhichonepartinglevelmustopenforthesprueandrunnersandthe

therpartinglevelmustopentoallowtheproductstofalldown.Theclassicdesignof latch unit is shown in the following figure a).A hinged latch bar remains in itsngagedpositionoveracertaindistanceandthenopensbytheactionofacam.When

sprin

wostageejection

sinner

geofejection to remove theparts from thecamsor themould force forming the fea

dmmotions es. The return travel iso

F TwoStageejection:concept(left)andapplicationexamp

Twofile ontheoutsidemould.tepplaoaethemouldisclosed,aleafspringholdsthehookinthelockedposition.Properfunctionofthis gmustbecheckedwhenassemblingthisunit.

T

Latchesdevices

Core

EjectorpinSlidingsleeve

EjectorpinSlidingsleeve

Core

Ejectionmotionofthehydraulicsystems of the machine

Ejectionmotionof

mould

opening

Latchlockingdevice

CAEDSMouldDesign

Ejectorpinsandsleeves16

Anotherdesignofa latchingunit isshown in following figureb).Both thehousingandthebaseplatearemountedonthepulledplate.It isrecommendedtoscrewthelatchbaron themovablemouldhalf and the controlbaron the fixedhalf.Duringmould opening,partingplane I opens first,until the slope S of the control bar (2)disengagestheslidinglock(3).PartingplaneIInowstartstoopen.Thestrokeofthepulledplateistobelimitedinthisposition,e.g.,withshoulderscrews.Thelengthofthe slopecorresponds to theminimum strokeof the latchlockingunit. In thisarea,onlylow

Duringmouldopeningmovement,ifthereisanothermotionwithinthemouldbefore

. In this case the latch stroke H tualookingstarts.

igure18 Standardlatchpullers:a)latchpullerwithslidehingedlatchbar;b)Latchevice;c)Latchlickingunitandoperatingsequence:I,II,IIIMouldpartinglines1Latchbar2Controlbar3SlidingboltSSlopeHvLostmotion

thquiredeopeningofpartingplane I starts,a thirdpartingplanemustbeprovidedas re

bar travels the delayed v before the ach

Fd

a)

c)

b)

CAEDSMouldDesign

Ejectorpinsandsleeves17

Althoughtheabovementionedlatchingunitsaremountedfromtheoutside,therearealsoroundlatchingunitsavailablethatareassembledinboresinsidethemould.Socalledfrictionpullersmaybeusedtoadvantageformediumpullingforcesandwherepositioning accuracy is not important. They transmit axial forces through frictionbetweenaplasticsleeveand theborewall.The friction force is infinitelyadjustablewithatapered,selflockingscrew.Thesestandarditemscanalsobeusedeffectivelyinthreeplatemolds;theycanalsobeusedasa braketoslowdownamotionorasadampertopreventshockswhenplatescollide.Thestrokeofthefloatingplatemust

rictionpuller

be limited in thedirectionofpulling, e.g.,by shoulder screws.Note thatwhen themouldisbeingclosed,themouldprotectionmechanismofthemachineisaffectedbythesefrictionalpullers.Lubricationofthepullersisnotpermissible.

Figure19 Frictionpuller

F

CAEDSMouldDesign

Ejectorpinsandsleeves18

CAEDSMouldDesign

Ejectorpinsandsleeves18

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Moldengineering,HerbertRees,Hanser/GardnerPublications,Inc.,ISBN1569901317,1995

UnderstandinginjectionMoldDesign,HerbertRees,HanserPublishers,ISBN1569903115,2001

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Howtomakeinjectionmolds,GeorgMenges,WalterMichaeliePaulMohren,3rded.,Munich:Hanser,ISBN3446212566,2001

Plasticsmoldengineeringhandbook,JohnHarryDubois(Author),WayneI.Pribble(Editor),KluwerAcademicPub;4thedition,ISBN0442218974,1987

ngineeringPolymers,partandmolddesignadesignguide,BayerCorporation,,2000

HASCO,DMEandCUMSAelectroniccatalogues

EPittsburgh

Ejector pins and sleevesReferences