注塑成型优化方法有出处中英文翻译.docx
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注塑成型优化方法有出处中英文翻译.docx
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注塑成型优化方法有出处中英文翻译
Atechnicalnoteonthecharacterizationofelectroformednickelshellsfortheirapplicationtoinjectionmolds
——UniversidaddeLasPalmasdeGranCanaria,DepartamentodeIngenieriaMecanica,Spain
Abstract
Thetechniquesofrapidprototypingandrapidtoolinghavebeenwidelydevelopedduringthelastyears.Inthisarticle,electroformingasaproceduretomakecoresforplasticsinjectionmoldsisanalysed.ShellsareobtainedfrommodelsmanufacturedthroughrapidprototypingusingtheFDMsystem.Themainobjectiveistoanalyzethemechanicalfeaturesofelectroformednickelshells,studyingdifferentaspectsrelatedtotheirmetallographicstructure,hardness,internalstressesandpossiblefailures,byrelatingthesefeaturestotheparametersofproductionoftheshellswithanelectroformingequipment.Finallyacorewastestedinaninjectionmold.
Keywords:
Electroplating;Electroforming;Microstructure;Nickel
ArticleOutline
1.Introduction
2.Manufacturingprocessofaninjectionmold
3.Obtaininganelectroformedshell:
theequipment
4.Obtainedhardness
5.Metallographicstructure
6.Internalstresses
7.Testoftheinjectionmold
8.Conclusions
References
1.Introduction
Oneofthemostimportantchallengeswithwhichmodernindustrycomesacrossistooffertheconsumerbetterproductswithoutstandingvarietyandtimevariability(newdesigns).Forthisreason,modernindustrymustbemoreandmorecompetitiveandithastoproducewithacceptablecosts.Thereisnodoubtthatcombiningthetimevariableandthequalityvariableisnoteasybecausetheyfrequentlyconditiononeanother;thetechnologicaladvancesintheproductivesystemsaregoingtopermitthatcombinationtobemoreefficientandfeasibleinawaythat,forexample,ifitisobservedtheevolutionofthesystemsandtechniquesofplasticsinjection,wearriveattheconclusionthat,infact,ittakeslessandlesstimetoputanewproductonthemarketandwithhigherlevelsofquality.Themanufacturingtechnologyofrapidtoolingis,inthisfield,oneofthosetechnologicaladvancesthatmakespossibletheimprovementsintheprocessesofdesigningandmanufacturinginjectedparts.Rapidtoolingtechniquesarebasicallycomposedofacollectionofproceduresthataregoingtoallowustoobtainamoldofplasticparts,insmallormediumseries,inashortperiodoftimeandwithacceptableaccuracylevels.Theirapplicationisnotonlyincludedinthefieldofmakingplasticinjectedpieces[1],[2]and[3],however,itistruethatitiswheretheyhavedevelopedmoreandwheretheyfindthehighestoutput.
Thispaperisincludedwithinawiderresearchlinewhereitattemptstostudy,define,analyze,testandpropose,atanindustriallevel,thepossibilityofcreatingcoresforinjectionmoldsstartingfromobtainingelectroformednickelshells,takingasaninitialmodelaprototypemadeinaFDMrapidprototypingequipment.
Italsowouldhavetosaybeforehandthattheelectroformingtechniqueisnotsomethingnewbecauseitsapplicationsintheindustryarecountless[3],butthisresearchworkhastriedtoinvestigatetowhatextentandunderwhichparameterstheuseofthistechniqueintheproductionofrapidmoldsistechnicallyfeasible.Allmadeinanaccurateandsystematizedwayofuseandproposingaworkingmethod.
2.Manufacturingprocessofaninjectionmold
Thecoreisformedbyathinnickelshellthatisobtainedthroughtheelectroformingprocess,andthatisfilledwithanepoxicresinwithmetallicchargeduringtheintegrationinthecoreplate[4]Thismold(Fig.1)permitsthedirectmanufacturingbyinjectionofatypeamultipleusespecimen,astheyaredefinedbytheUNE-ENISO3167standard.Thepurposeofthisspecimenistodeterminethemechanicalpropertiesofacollectionofmaterialsrepresentativeindustry,injectedinthesetoolsanditscoMParisonwiththepropertiesobtainedbyconventionaltools.
Thestagestoobtainacore[4],accordingtothemethodologyresearchedinthiswork,arethefollowing:
(a)DesigninCADsystemofthedesiredobject.
(b)Modelmanufacturinginarapidprototypingequipment(FDMsystem).ThematerialusedwillbeanABSplastic.
(c)Manufacturingofanickelelectroformedshellstartingfromthepreviousmodelthathasbeencoatedwithaconductivepaintbeforehand(itmusthaveelectricalconductivity).
(d)Removaloftheshellfromthemodel.
(e)Productionofthecorebyfillingthebackoftheshellwithepoxyresinresistanttohightemperaturesandwiththerefrigeratingductsmadewithcoppertubes.
Theinjectionmoldhadtwocavities,oneofthemwastheelectroformedcoreandtheotherwasdirectlymachinedinthemovingplaten.Thus,itwasobtained,withthesametoolandinthesameprocessconditions,toinjectsimultaneouslytwospecimensincavitiesmanufacturedwithdifferenttechnologies.
3.Obtaininganelectroformedshell:
theequipment
Electrodeposition[5]and[6]isanelectrochemicalprocessinwhichachemicalchangehasitsoriginwithinanelectrolytewhenpassinganelectriccurrentthroughit.Theelectrolyticbathisformedbymetalsaltswithtwosubmergedelectrodes,ananode(nickel)andacathode(model),throughwhichitismadetopassanintensitycomingfromaDCcurrent.Whenthecurrentflowsthroughthecircuit,themetalionspresentinthesolutionaretransformedintoatomsthataresettledonthecathodecreatingamoreorlessuniformdepositlayer.
Theplatingbathusedinthisworkisformedbynickelsulfamate[7]and[8]ataconcentrationof400 ml/l,nickelchloride(10 g/l),boricacid(50 g/l),AllbriteSLA(30 cc/l)andAllbrite703(2 cc/l).Theselectionofthiscompositionismainlyduetothetypeofapplicationweintend,thatistosay,injectionmolds,evenwhentheinjectionismadewithfibreglass.Nickelsulfamateallowsustoobtainanacceptablelevelofinternalstressesintheshell(thetestsgaveresults,fordifferentprocessconditions,notsuperiorto50 MPaandforoptimumconditionsaround2 MPa).Nevertheless,suchlevelofinternalpressureisalsoaconsequenceofusingasanadditiveAllbriteSLA,whichisastressreducerconstitutedbyderivativesoftoluenesulfonamideandbyformaldehydeinaqueoussolution.Suchadditivealsofavourstheincreaseoftheresistanceoftheshellwhenpermittingasmallergrain.Allbrite703isanaqueoussolutionofbiodegradablesurface-actingagentsthathasbeenutilizedtoreducetheriskofpitting.Nickelchloride,inspiteofbeingharmfulfortheinternalstresses,isaddedtoenhancetheconductivityofthesolutionandtofavourtheuniformityinthemetallicdistributioninthecathode.TheboricacidactsasapHbuffer.
Theequipmentusedtomanufacturethenickelshellstestedhasbeenasfollows:
•Polypropylenetank:
600 mm × 400 mm × 500 mminsize.
•Threeteflonresistors,eachonewith800 W.
•Mechanicalstirringsystemofthecathode.
•Systemforrecirculationandfiltrationofthebathformedbyapumpandapolypropylenefilter.
•Chargingrectifier.Maximumintensityincontinuous50 Aandcontinuouscurrentvoltagebetween0and16 V.
•Titaniumbasketwithnickelanodes(IncoS-RoundsElectrolyticNickel)withapurityof99%.
•Gasesaspirationsystem.
Oncethebathhasbeendefined,theoperativeparametersthathavebeenalteredfortestingdifferentconditionsoftheprocesshavebeenthecurrentdensity(between1and22 A/dm2),thetemperature(between35and55 °C)andthepH,partiallymodifyingthebathcomposition.
4.Obtainedhardness
Oneofthemostinterestingconclusionsobtainedduringthetestshasbeenthatthelevelofhardnessofthedifferentelectroformedshellshasremainedatratherhighandstablevalues.InFig.2,itcanbeobservedthewayinwhichforcurrentdensityvaluesbetween2.5and22 A/dm2,thehardnessvaluesrangefrom540and580 HV,atpH4 ± 0.2andwithatemperatureof45 °C.IfthepHofthebathisreducedat3.5andthetemperatureis55 °Cthosevaluesareabove520 HVandbelow560 HV.Thisfeaturemakesthetestedbathdifferentfromotherconventionalonescomposedbynickelsulfamate,allowingtooperatewithawiderrangeofvalues;nevertheless,suchoperativitywillbelimiteddependingonotherfactors,suchasinternalstressbecauseitsvariabilitymayconditiontheworkatcertainvaluesofpH,currentdensityortemperature.Ontheotherhand,thehardnessofaconventionalsulfamatebathisbetween200–250 HV,muchlowerthantheoneobtainedinthetests.Itisnecessarytotakeintoaccountthat,foraninjectionmold,thehardnessisacceptablestartingfrom300 HV.Amongthemostusualmaterialsforinjectionmoldsitispossibletofindsteelforimprovement(290 HV),steelforintegralhardening(520–595 HV),casehardenedsteel(760–800 HV),etc.,insuchawaythatitcanbeobservedthatthehardnesslevelsofthenickelshellswouldbewithinthemedium–highrangeofthematerialsforinjectionmolds.Theobjectiontothelowductilityoftheshelliscompensatedinsuchawaywiththeepoxyresinfillingthatwouldfollowitbecausethisistheoneresponsibleforholdinginwardlythepressurechargesoftheprocessesofplasticsinjection;thisisthereasonwhyitisnecessaryfortheshelltohaveathicknessashomogeneousaspossible(aboveaminimumvalue)andwithabsenceofimportantfailuressuchaspitting.
5.Metallographicstructure
Inordertoanalyzethemetallographicstructure,thevaluesofcurrentdensityandtemperatureweremainlymodified.Thesampleswereanalyzedinfrontalsectionandintransversalsection(perpendiculartothedeposition).Forachievingaconvenientpreparation,theywereconvenientlyencapsulatedinre
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