毕业设计论文外文翻译译文 2.docx

毕业设计论文外文翻译译文 2.docx

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毕业设计论文外文翻译译文2

编号：

毕业设计（论文）外文翻译

（原文）

学院：

机电工程学院

专业：

机械设计制造及其自动化

学生姓名：

刘腾飞

学号：

0801120829

指导教师单位：

艺术与设计学院

姓名：

梁惠萍

职称：

讲师

2012年5月15日

TheEffectsofMoldDesignonthePoreMorphologyofPolymersProducedwithMuCell_Technology

ABSTRACT:

InthisstudytwomoldsweredesignedandusedinMuCell_technologytogenerateimplantswithaporousstructure.Toarrivethedesiredporestructuremanyprocessparameterswereinvestigatedforindicatingtheeffectsofprocessparametersontheporemorphology.Thisprocessparameterinvestigationwasperformedoneachmoldrespectively,sothattheinfluencesofthemolddesignontheporemorphologyhavebeenresearchedbythesameprocessparametersetting.ItwasfoundthatthemolddesignalsohadeffectsontheporestructureinMuCell_technology.Apropermolddesigncouldimprovethegeneratedporestructure,suchasporosity,porediameter,andinterconnectivity.

KEYWORDS:

molddesign,cellmorphology,MuCell_,injectionmolding,medicalimplant,porouspolymer,polyurethane.

INTRODUCTION

MuCelltechnology,asaneffectivemicrocellularinjectionmoldingprocess,iswidelyusedinautomobileandfurnitureindustries.Inmostcases,MuCell_technologyisusedtosaverawmaterials,butitisalsousedtoproduceimplantswithclosedporousstructure[1].ItusesCO2asblowingagent,whichisinjectedintheplasticizationsectionoftheinjectionmoldingmachine（Figure1）.Theblowingagentisinjectedintothepolymermeltthroughthegassupplylineandinjector,initssupercriticalstate,bytheplasticizationphaseoftheinjectionmoldingmachine.Aftertheplasticizationthemixtureofpolymermeltandgasisinjectedthroughthenozzleintothemold,wherethefoamstructurecanbegeneratedduetothequickpressuredropinthemold.ThemainproductswhichareproducedtodaywithMuCell_technologyhaveclosedcellularfoam[2–4].

TheMuCellMicrocellularFoaminjectionmoldingtechnologyisacompleteprocessandequipmenttechnologywhichfacilitatesextremelyhighqualityandgreatlyreducesproductioncosts. TheMuCellProcessinvolvesthecontrolleduseofgasinitssupercriticalstatetocreateafoamedpart.TheMuCellTechnologyistargetedatprecisionandengineeredplasticcomponentswithmaximumwallthicknessesoflessthan3mm.TheMuCellProcessgenerallyoffersa50-75%improvementinkeyqualitymeasures,suchasflatness,roundness,andwarpage,alsoeliminatingallsinkmarks.Theseimprovementsresultfromthefactthatrelativelyuniformstresspatternsarecreatedinthemoldedpartratherthannonuniformstresscharacteristicofsolidmolding.AsadirectresultoftheuniformstressandshrinkageassociatedwiththeMuCellProcess（whichoccursbecausethepackandholdphaseofthemoldingcycleiseliminated）,thepartsthatareproducedtendtocomplyfarmorecloselywiththemoldshapeand,presumably,thedimensionalspecificationsofthepartitself.ThismeansthatwhenusingtheMuCellProcess,fewermolditerationsareneededtoproduceacompliantpart,savingtimeandcost.ThequalityadvantagesoftheMuCellProcessarecomplementedbycertaindirecteconomicadvantages,includingtheabilitytoproduce20-33%morepartsperhouronagivenmoldedmachine,andtheabilitytomoldpartsonlowertonnagemachinesasaresultoftheviscosityreductionandtheeliminationofthepackingrequirementthataccompaniestheuseofsupercriticalgas.This25pageprocessinghandbookcoversallaspectsoftheprocessfromset-uptotroubleshootingtooptimizingresults.ItisprimarilyusefultocompanieswhoaremanufacturingorareplanningtomanufacturepartsusingtheMuCellInjectionMoldingProcess.PleasecontactTrexelforacopyofthispublication.TheMuCellInjectionMoldingProcessinvolvesthehighlycontrolleduseofgasinitssupercriticalstate（SCF）tocreatedmillionsofmicron-sizedvoidsinthinwallmoldedparts（lessthan3mm）. Withthecorrectequipmentconfiguration,molddesign,andprocessingconditionsthesemicrocellularvoidsarerelativelyuniforminsizeanddistribution.Thevoidsarecreatedornucleatedasaresultofhomogeneousnucleationthatoccurswhenasingle-phasesolutionofpolymerandgas（commonlynitrogen,butoccasionallycarbondioxide）passesthroughtheinjectiongateintothemold.Thesingle-phasesolutioniscreatedthroughtheoperationofaconventionalinjectionmoldingmachinewhichhasbeenmodifiedtoallowthecreationofasingle-phasesolution. ThekeymodificationstothesysteminvolvetheuseofaprecisionSCFdeliverysystemtodeliverSCFtospecialinjectorsbasedonmassflowmeteringprinciples. TheSCFistheninjectedintothebarrelwhereitismixedwiththepolymerviaaspeciallydesignedscrew. Ashutoffnozzlemaintainsthesinglephasesolutionwhiletheinjectionmoldingscrewmaintainssufficientbackpressureatalltimestopreventprematurefoamingorthelossofpressurewhichwouldallowthesinglephasesolutiontoreturntothetwophasesolution. TrexelhasrecentlypublishedacomprehensiveMuCellProcessGuideinEnglish,Chinese,Japanese,andGermanwhichexplainsinstepbystepdetailhowtoapplytheMuCellprocessinthemanufactureofMuCellInjectionMoldedcomponents.This25pageprocessinghandbookcoversallaspectsoftheprocessfromset-uptotroubleshootingtooptimizingresults.ItisprimarilyusefultocompanieswhoaremanufacturingorareplanningtomanufacturepartsusingtheMuCellInjectionMoldingProcess.PleasecontactTrexelforacopyofthispublication.TheMuCellmicrocellularfoaminjectionmoldingprocessforthermoplasticsmaterialsprovidesuniquedesignflexibilityandcostsavingsopportunitiesnotfoundinconventionalinjectionmolding.TheMuCellprocessallowsforplasticpartdesignwithmaterialwallthicknessoptimizedforfunctionalityandnotfortheinjectionmoldingprocess.Thecombinationofdensity

reductionanddesignforfunctionalityoftenresultsinmaterialandweightsavingsofmorethan20%.

Byreplacingthepack&holdphasewithcellgrowth,lowerstresspartsareproducedwhichhaveenhanceddimensionalstabilityandsubstantiallyreducewarpage.Cellgrowthalsoresultsintheeliminationofsinkmarks.

Unlikechemicalfoamingagents,thephysicalMuCellprocesshasnotemperaturelimitationanddoesnotleaveanychemicalresidueinthepolymer;makingconsumerproductsperfectlysuitableforrecyclingwithintheoriginalpolymerclassificationandallowingre-grindmaterialtoreentertheprocessflow.

ThenumerouscostandprocessingadvantageshaveledtorapidglobaldeploymentoftheMuCellprocessprimarilyinautomotive,consumerelectronics,medicaldevice,packagingandconsumergoodsapplications.Microcellularfoamsrefertothermoplasticfoamswithcellsoftheorderof10µminsize.Typicallythesefoamsarerigid,closed-cellstructures;althoughrecentlythereismuchinterestincreatingopen-cell,porousstructuresthathavecellsinthissizerange.ThemicrocellularprocessthatsparkedthegrowthinthisfieldoverthepasttwodecadeswasinventedatMassachusettsInstituteofTechnology,USA,inearlyeighties[1],inresponsetoachallengebyfoodandfilmpackagingcompaniestoreducetheamountofpolymerusedintheirindustries.Asmostoftheseapplicationsusedsolid,thin-walledplastics,reducingtheirdensitiesbytraditionalfoamingprocessesthatproducedbubbleslargerthan0.25mmwasnotfeasibleduetoexcessivelossofstrength.Thuswasborntheideatocreatemicrocellularfoam,wherewecouldhave,forexample,100bubblesacrossonemmthickness,andexpecttohaveareasonablestrengthfortheintendedapplications.

Itwouldbereasonabletosaythatthepotentialofmicrocellularfoamshasyettoberealized.Thesematerialshavenotyetappearedinmassproducedplasticitems,andthepromisedsavingsinmaterialsandassociatedcostshaveyettomaterialize.Thisislargelyduetomanufacturingdifficultiesencounteredinscalingupforlargescaleproduction.However,enthusiasmforthesematerialsremainshigh,andtodayresearchersandcommercialenterprisesoneverycontinentareinaglobalracetoharnessthepotentialbenefits.

Muchhasbeenlearnedabouttheprocessingandpropertiesofmicrocellularfoamssincethefirstpatentwasgrantedin1984[2].Anearlyreviewofthesubjectappearedin1993[3].Inthischapterthestate-of-theartofprocessingwillbereviewedinthenextsection,followedbyadiscussionofstructureandproperties.Thischapterwillconcludewithalookatsomeofthecurrentresearchdirectionsinvolvingmicrocellulartechnology.

Althoughinnovationsinprocessinghavedevelopedatarapidpace,thepropertydataonmicrocellularfoamshasbeenslowincoming.Theearlypublicationsonmicrocellularfoamsconjecturedthatthemicrocellularstructure,believedtobeonascalethatwassmallerthanthe‘criticalflawsize’forpolymers,wouldenablethesefoamstoretaintheirmechanicalpropertiesevenasthedensitywasreduced.Noquantitativeinformationonthecriticalflawsizewaseverpresented,norwasanypropertydatapresentedinsupportofthehypothesis.Thisislikelytobeduetotheemphasisplacedonprocessdevelopment,asopposedtopropertycharacterization,intheearlyyearsofevolutionofthisfield.Overtime,however,thisconjecturehasbecomeamyththatmicrocellularmaterialsareasstrongasthesolidpolymersbuthavealowerdensity,thusprovidinganopportunitytolowercostswithnopenaltyinperformance.

Thetensilepropertydata[4]showsthatthetensilestrengthofmicrocellularfoamsdecreasesinproportiontothefoamdensity,andcanbeapproximatedquitewellbytheruleofmixtures.Thusa50%rel