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JournalofMaterialsProcessingTechnology176(2006)273–277Abstractprocedurethemetallographicwith©K1.industrywiththisitidoubtablethetointhetheaityfield,theturingcomposedusinTheir0924-0136/$doi:AtechnicalnoteonthecharacterizationofelectroformednickelshellsfortheirapplicationtoinjectionmoldsMarioD.Monzon,M.DoloresMarrero,A.NizardoBenitez,PedroM.Hernandez,J.FranciscoCardenesUniversidaddeLasPalmasdeGranCanaria,DepartamentodeIngenieriaMecanica,SpainReceived19November2003;receivedinrevisedform14January2006;accepted11April2006Thetechniquesofrapidprototypingandrapidtoolinghavebeenwidelydevelopedduringthelastyears.Inthisarticle,electroformingasatomakecoresforplasticsinjectionmoldsisanalysed.ShellsareobtainedfrommodelsmanufacturedthroughrapidprototypingusingFDMsystem.Themainobjectiveistoanalyzethemechanicalfeaturesofelectroformednickelshells,studyingdifferentaspectsrelatedtotheirstructure,hardness,internalstressesandpossiblefailures,byrelatingthesefeaturestotheparametersofproductionoftheshellsanelectroformingequipment.Finallyacorewastestedinaninjectionmold.2006ElsevierB.V.Allrightsreserved.eywords:Electroplating;Electroforming;Microstructure;NickelIntroductionOneofthemostimportantchallengeswithwhichmoderncomesacrossistooffertheconsumerbetterproductsplasticinjectedpieces[1–3],however,itistruethatitiswheretheyhavedevelopedmoreandwheretheyfindthehighestoutput.Thispaperisincludedwithinawiderresearchlinewhereitoutstandingvarietyandtimevariability(newdesigns).Forreason,modernindustrymustbemoreandmorecompet-veandithastoproducewithacceptablecosts.Thereisnothatcombiningthetimevariableandthequalityvari-isnoteasybecausetheyfrequentlyconditiononeanother;technologicaladvancesintheproductivesystemsaregoingpermitthatcombinationtobemoreefficientandfeasibleawaythat,forexample,ifitisobservedtheevolutionofsystemsandtechniquesofplasticsinjection,wearriveatconclusionthat,infact,ittakeslessandlesstimetoputnewproductonthemarketandwithhigherlevelsofqual-.Themanufacturingtechnologyofrapidtoolingis,inthisoneofthosetechnologicaladvancesthatmakespossibleimprovementsintheprocessesofdesigningandmanufac-injectedparts.Rapidtoolingtechniquesarebasicallyofacollectionofproceduresthataregoingtoallowtoobtainamoldofplasticparts,insmallormediumseries,ashortperiodoftimeandwithacceptableaccuracylevels.applicationisnotonlyincludedinthefieldofmakingE-mailaddress:[email protected](M.D.Monzon).attemptstrialstartinganequipment.formingcationswparametersrapidratemethod.2.throughepoxiccoreing–seefrontmatter©2006ElsevierB.V.Allrightsreserved.10.1016/j.jmatprotec.2006.04.003tostudy,define,analyze,testandpropose,atanindus-level,thepossibilityofcreatingcoresforinjectionmoldsfromobtainingelectroformednickelshells,takingasinitialmodelaprototypemadeinaFDMrapidprototypingItalsowouldhavetosaybeforehandthattheelectro-techniqueisnotsomethingnewbecauseitsappli-intheindustryarecountless[3],butthisresearchorkhastriedtoinvestigatetowhatextentandunderwhichtheuseofthistechniqueintheproductionofmoldsistechnicallyfeasible.Allmadeinanaccu-andsystematizedwayofuseandproposingaworkingManufacturingprocessofaninjectionmoldThecoreisformedbyathinnickelshellthatisobtainedtheelectroformingprocess,andthatisfilledwithanresinwithmetallicchargeduringtheintegrationintheplate[4]Thismold(Fig.1)permitsthedirectmanufactur-byinjectionofatypeamultipleusespecimen,astheyare274Processingdefinedspecimentionandtools.researched(a)(b)(c)(d)(e)Theformedplaten.processca3.whichwhenbathanmadethethecathodesulf(10703tomolds,sulfstressesconditions,aroundalsoisamidealsopermittingoftoharmfultidistribhasM.D.Monzonetal./JournalofMaterialsFig.1.Manufacturedinjectionmoldwithelectroformedcore.bytheUNE-ENISO3167standard.Thepurposeofthisistodeterminethemechanicalpropertiesofacollec-ofmaterialsrepresentativeindustry,injectedinthesetoolsitscoMParisonwiththepropertiesobtainedbyconventionalThestagestoobtainacore[4],accordingtothemethodologyinthiswork,arethefollowing:DesigninCADsystemofthedesiredobject.Modelmanufacturinginarapidprototypingequipment(FDMsystem).ThematerialusedwillbeanABSplastic.Manufacturingofanickelelectroformedshellstartingfromthepreviousmodelthathasbeencoatedwithaconductivepaintbeforehand(itmusthaveelectricalconductivity).Removaloftheshellfromthemodel.Productionofthecorebyfillingthebackoftheshellwithepoxyresinresistanttohightemperaturesandwiththerefrigeratingductsmadewithcoppertubes.injectionmoldhadtwocavities,oneofthemwastheelectro-coreandtheotherwasdirectlymachinedinthemovingThus,itwasobtained,withthesametoolandinthesameconditions,toinjectsimultaneouslytwospecimensinvitiesmanufacturedwithdifferenttechnologies.Obtaininganelectroformedshell:theequipmentElectrodeposition[5,6]isanelectrochemicalprocessinachemicalchangehasitsoriginwithinanelectrolytepassinganelectriccurrentthroughit.Theelectrolyticisformedbymetalsaltswithtwosubmergedelectrodes,anode(nickel)andacathode(model),throughwhichitistopassanintensitycomingfromaDCcurrent.Whencurrentflowsthroughthecircuit,themetalionspresentinsolutionaretransformedintoatomsthataresettledonthecreatingamoreorlessuniformdepositlayer.Theplatingbathusedinthisworkisformedbynickelamate[7,8]ataconcentrationof400ml/l,nickelchlorideg/l),boricacid(50g/l),AllbriteSLA(30cc/l)andAllbrite(2cc/l).Theselectionofthiscompositionismainlyduethetypeofapplicationweintend,thatistosay,injectionevenwhentheinjectionismadewithfibreglass.Nickelamateallowsustoobtainanacceptablelevelofinternal•••••••hahatemperatureifying4.testsformedFig.vfromofperature560conoperateTechnology176(2006)273–277intheshell(thetestsgaveresults,fordifferentprocessnotsuperiorto50MPaandforoptimumconditions2MPa).Nevertheless,suchlevelofinternalpressureisaconsequenceofusingasanadditiveAllbriteSLA,whichastressreducerconstitutedbyderivativesoftoluenesulfon-andbyformaldehydeinaqueoussolution.Suchadditivefavourstheincreaseoftheresistanceoftheshellwhenasmallergrain.Allbrite703isanaqueoussolutionbiodegradablesurface-actingagentsthathasbeenutilizedreducetheriskofpitting.Nickelchloride,inspiteofbeingfortheinternalstresses,isaddedtoenhancetheconduc-vityofthesolutionandtofavourtheuniformityinthemetallicutioninthecathode.TheboricacidactsasapHbuffer.Theequipmentusedtomanufacturethenickelshellstestedbeenasfollows:Polypropylenetank:600mm×400mm×500mminsize.Threeteflonresistors,eachonewith800W.Mechanicalstirringsystemofthecathode.Systemforrecirculationandfiltrationofthebathformedbyapumpandapolypropylenefilter.Chargingrectifier.Maximumintensityincontinuous50Aandcontinuouscurrentvoltagebetween0and16V.Titaniumbasketwithnickelanodes(IncoS-RoundsElec-trolyticNickel)withapurityof99%.Gasesaspirationsystem.Oncethebathhasbeendefined,theoperativeparametersthatvebeenalteredfortestingdifferentconditionsoftheprocess2vebeenthecurrentdensity(between1and22A/dm),the(between35and55◦C)andthepH,partiallymod-thebathcomposition.ObtainedhardnessOneofthemostinterestingconclusionsobtainedduringthehasbeenthatthelevelofhardnessofthedifferentelectro-shellshasremainedatratherhighandstablevalues.In2,itcanbeobservedthewayinwhichforcurrentdensityaluesbetween2.5and22A/dm2,thehardnessvaluesrange540and580HV,atpH4±0.2andwithatemperature45◦C.IfthepHofthebathisreducedat3.5andthetem-is55◦Cthosevaluesareabove520HVandbelowHV.Thisfeaturemakesthetestedbathdifferentfromotherventionalonescomposedbynickelsulfamate,allowingtowithawiderrangeofvalues;nevertheless,suchopera-Fig.2.Hardnessvariationwithcurrentdensity.pH4±0.2,T=45◦C.ProcessingTechnology176(2006)273–277275tistresstainhand,200–250isthemoststeel(520–595anickmaterialsoffillingforplasticsshellminimumpitting.5.currentples(perpendicularpreparation,ishedacid15,observPME3-ADLarticle,thethelayerapproximatelyzontalThus,thegoingthebemolds:TTSeries1234Fig.3.Series1(×150),etch1.Fig.4.Series2(×300),etch2.M.D.Monzonetal./JournalofMaterialsvitywillbelimiteddependingonotherfactors,suchasinternalbecauseitsvariabilitymayconditiontheworkatcer-valuesofpH,currentdensityortemperature.OntheotherthehardnessofaconventionalsulfamatebathisbetweenHV,muchlowerthantheoneobtainedinthetests.Itnecessarytotakeintoaccountthat,foraninjectionmold,hardnessisacceptablestartingfrom300HV.Amongtheusualmaterialsforinjectionmoldsitispossibletofindforimprovement(290HV),steelforintegralhardeningHV),casehardenedsteel(760–800HV),etc.,insuchwaythatitcanbeobservedthatthehardnesslevelsoftheelshellswouldbewithinthemedium–highrangeoftheforinjectionmolds.Theobjectiontothelowductilitytheshelliscompensatedinsuchawaywiththeepoxyresinthatwouldfollowitbecausethisistheoneresponsibleholdinginwardlythepressurechargesoftheprocessesofinjection;thisisthereasonwhyitisnecessaryforthetohaveathicknessashomogeneousaspossible(aboveavalue)andwithabsenceofimportantfailuressuchasMetallographicstructureInordertoanalyzethemetallographicstructure,thevaluesofdensityandtemperatureweremainlymodified.Thesam-wereanalyzedinfrontalsectionandintransversalsectiontothedeposition).Forachievingaconvenienttheywereconvenientlyencapsulatedinresin,pol-andetchedindifferentstageswithamixtureofaceticandnitricacid.Theetchesarecarriedoutatintervalsof25,40and50s,afterbeingpolishedagain,inordertobeedafterwardsinametallographicmicroscopeOlympus3.3×/10×.BeforegoingontocommentthephotographsshowninthisitisnecessarytosaythatthemodelsusedtomanufactureshellsweremadeinaFDMrapidprototypingmachinewheremoltenplasticmaterial(ABS),thatlatersolidifies,issettledbylayer.Ineachlayer,theextruderdieleavesathread0.15mmindiameterwhichiscompactedhori-andverticallywiththethreadsettledinmediatelyafter.inthesurfaceitcanbeobservedthinlinesthatindicateroadsfollowedbytheheadofthemachine.Theselinesaretoactasareferencetoindicatethereproducibilitylevelofnickelsettled.Thereproducibilityofthemodelisgoingtoafundamentalelementtoevaluateabasicaspectofinjectionthesurfacetexture.ThetestedseriesareindicatedinTable1.able1estedseriespHTemperature(◦C)Currentdensity(A/dm2)4.2±0.2552.223.9±0.2455.564.0±0.24510.004.0±0.24522.22firstthatstillalessetchisdarkconditionsFig.3illustratesthesurfaceofasampleoftheseriesaftertheetch.ItshowstheroadsoriginatedbytheFDMmachine,istosaythatthereisagoodreproducibility.Itcannotbenoticedtheroundedgrainstructure.InFig.4,series2,aftersecondetch,itcanbeobservedalineoftheroadinawayclearthaninthepreviouscase.InFig.5,series3and2◦itbeginstoappeartheroundedgrainstructurealthoughitverydifficulttochecktheroadsatthistime.Besides,themostenedareasindicatethepresenceofpittingbyinadequateofprocessandbathcomposition.Fig.5.Series3(×300),etch2.276Processingandmodelfordeposition,ditionswhatalthoughabosulfnon-laminarvturetheSLA).turecurrent6.applicationDiftiestensiometerwithwidthonlysilestresses.nickintestedforacceptableistionsstresses.M.D.Monzonetal./JournalofMaterialsFig.6.Planetransversalofseries2(×600),etch2.Thisbehaviorindicatesthat,workingatalowcurrentdensityahightemperature,shellswithagoodreproducibilityoftheandwithasmallgrainsizeareobtained,thatis,adequatetherequiredapplication.Iftheanalysisiscarriedoutinaplanetransversaltotheitcanbetestedinallthesamplesandforallthecon-thatthegrowthstructureofthedepositislaminar(Fig.6),isverysatisfactorytoobtainahighmechanicalresistanceattheexpenseofalowductibility.Thisqualityisdue,veall,tothepresenceoftheadditivesusedbecauseanickelamatebathwithoutadditivesnormallycreatesafibrousandstructure[9].Themodificationuntilanearlynullalueofthewettingagentgaveasaresultthatthelaminarstruc-wasmaintainedinanycase,thatmatterdemonstratedthatdeterminantforsuchstructurewasthestressreducer(AllbriteOntheotherhand,itwasalsotestedthatthelaminarstruc-variesaccordingtothethicknessofthelayerintermsofthedensity.InternalstressesOneofthemaincharacteristicthatashellshouldhaveforitslikeaninsertistohavealowlevelofinternalstresses.ferenttestsatdifferentbathtemperaturesandcurrentdensi-weredoneandameasuresystemrestedoncathodeflexuralmethodwasused.Asteeltestingcontrolwasusedasidefixedandtheotherfree(160mmlength,12.7mmandthickness0.3mm).Becausethemetallicdepositionisinonesidethetestingcontrolhasamechanicalstrain(ten-orcompressivestress)thatallowstocalculatetheinternalStoneymodel[10]wasappliedandwassupposedthatelsubstratumthicknessisenoughsmall(3H9262m)toinfluence,anelasticpointofview,tothestrainedsteelpart.Inallthecasesthemostvalueofinternalstresswasunder50MPaextremeconditionsand2MPaforoptimalconditions,anvaluefortherequiredapplication.Theconclusionthattheelectroliticbathallowstoworkatdifferentcondi-andparameterswithoutasignificantvariationofinternal7.moplastichasdimensions,calbycore,betweenthematerials.itofenceecrystallinenoticedcore,around8.checkhasertiesthatgoodstructure.becoreplasticReferTechnology176(2006)273–277Fig.7.Analysisbyphotoelasticityofinjectedspecimens.TestoftheinjectionmoldTestshavebeencarriedoutwithvariousrepresentativether-materialssuchasPP,PA,HDPEandPC,anditbeenanalysedthepropertiesoftheinjectedpartssuchasweight,resistance,rigidityandductility.Mechani-propertiesweretestedbytensiledestructivetestsandanalysisphotoelasticity.About500injectionswerecarriedoutonthisremainingunderconditionsofwithstandingmanymore.Ingeneralterms,importantdifferenceswerenotnoticedthebehaviorofthespecimensobtainedinthecoreandonesfromthemachinedcavity,forthesetoftheanalysedHoweverintheanalysisbyphotoelasticiy(Fig.7)wasnoticedadifferenttensionalstatebetweenbothtypesspecimens,basicallyduetodifferencesintheheattransfer-andrigidityoftherespectivemoldcavities.ThisdifferencexplainstheductilityvariationsmoreoutstandinginthepartiallymaterialssuchasHDPEandPA6.ForthecaseofHDPEinalltheanalysedtestedtubesitwasalowerductilityinthespecimensobtainedinthenickelquantifiedabout30%.InthecaseofPA6thisvaluewas50%.ConclusionsAfterconsecutivetestsandindifferentconditionsithasbeenedthatthenickelsulfamatebath,withtheutilizedadditivesallowedtoobtainnickelshellswithsomemechanicalprop-acceptablefortherequiredapplication,injectionmolds,istosay,goodreproducibility,highlevelofhardnessandmechanicalresistanceintermsoftheresultantlaminarThemechanicaldeficienciesofthenickelshellwillpartiallyreplacedbytheepoxyresinthatfinishesshapingthefortheinjectionmold,allowingtoinjectmediumseriesofpartswithacceptablequalitylevels.ences[1]A.E.W.Rennie,C.E.Bocking,G.R.Bennet,Electroformingofrapidpro-totypingmandrelsforelectrodischargemachiningelectrodes,J.Mater.Process.Technol.110(2001)186–196.[2]P.K.D.V.Yarlagadda,I.P.Ilyas,P.Chrstodoulou,Developmentofrapidtoolingforsheetmetaldrawingusingnickelelectroformingandstereolithographyprocesses,J.Mater.Process.Technol.111(2001)286–294.
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