Potential of Laser Engineered

PotentialofLaserEngineeredNetShaping(LENS)Technology

I.Palˇciˇc1,M.Balažic2,M.Milfelner3,andB.Buchmeister1

LaboratoryforProductionandOperationsManagement,FacultyofMechanicalEngineering,

UniversityofMaribor,Maribor,Slovenia

2

LaboratoryofCutting,FacultyofMechanicalEngineering,UniversityofLjubljana,Ljubljana,Slovenia

3

EMOTool-Shop,Celje,Slovenia

Thisarticlehasatwofoldpurpose.Thefirstpartdealswithintroductionofinnovativehightechnologylaserengineerednetshaping(LENS)thatoffersabreakthroughinmanufacturing,maintaining,andrepairingproducts.ItalsopresentsmanypossibilitiesfortheuseofLENStechnology,especiallyinthetool-makingindustryandformedicalpurposes.ThesecondpartpresentsacomparisonofaproductmanufacturedbyconventionaltechnologiesandthesameproductmanufacturedbyLENStechnology.Theproductisatitaniumalloymedicalimplant.

KeywordsHardness;Laser;Layermanufacturing;LENStechnology;Medicalimplant;Medicine;Microstructure;Nail;Rapidmanufacturing;Rapidprototyping;Rapidtooling;Titanium;Titaniumalloy;Tool;Tool-making.

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1.Introduction

Atleasttwoconditionshavetobefulfilledtomanufactureaproductwithahighaddedvalue.Weneedasophisticatedtechnologythatofferspossibilitiestomanufacturethemostdemandingproductsfromdifferentmaterials,andweneedbusinessideastoapplythetechnologyinareasthatcontributethemosttocompetitiveness.Laserengineerednetshaping(LENS)isoneofthesesophisticatedtechnologies,andithasmanyadvantagesincomparisonwithconventionaltechnologiesandmanyareasforapplication.Thisarticlewill,therefore,focusondescriptionoftheLENStechnologyanditsapplicationsindifferentareas,especiallyintool-makingindustryandformedicalpurposes.

2.LENStechnology

Layermanufacturingtechniques,alsocalledrapidprototypingtechniques,haveabout20yearsofhistory.Thesetechniquesdirectlyfabricate,layerbylayer,physicalmodelsfrom3-Dsolidmodelsproducedincomputer-aideddesign(CAD)[1].Layermanufacturingtechnologyisthekeytechnologyoftherapidprototypingsystem,anditallowsthefabricationofthree-dimensionalpartslayerbylayer.Selectivelasersintering(SLS),LENS,3Dwelding,microcasting,3Dcladding,andshapedepositionmanufacturing(SDM)aresomeimportantprocessesfortheRPsystem[2,3].OneofthemostpromisingisLENStechnologythatisusedtofabricatefullydensemetalpartsdirectlyfromCADsolidmodels.LENSisalaserfabricationtechniquedevelopedatSandiaNationalLaboratoryfor

ReceivedFebruary15,2008;AcceptedAugust15,2008AddresscorrespondencetoAssistantProfessorDr.I.Palcˇicˇ,FacultyofMechanicalEngineering,UniversityofMaribor,Smetanovaulica17,Maribor2000,Slovenia;E-mail:iztok.palcic@uni-mb.siproducingcomponentsthataredifficultorimpossibletoprocessthroughconventionalmetalformingtechniques.Theprocessissimilartotraditionallaser-initiatedrapidprototypingtechnologiessuchasstereolithographyandselectivelasersinteringinthatlayeradditivetechniquesareusedtofabricatephysicalpartsdirectlyfromCADdata.Byusingthecoordinateddeliveryofmetalparticlesintoafocusedlaserbeam,apartisgenerated.Thelaserbeamcreatesamoltenpoolofmetalonasubstrateintowhichpowderisinjected.Concurrently,thesubstrateonwhichthedepositionisoccurringismovedunderthebeam/powderinteractionzonetofabricatethedesiredcross-sectionalgeometry.Consecutivelayersareadditivelydeposited,therebyproducingathree-dimensionalpart[4–6].Thisprocessexhibitsenormouspotentialtorevolutionizethewayinwhichmetalparts,suchascomplexprototypes,tooling,andsmall-lotproductionparts,areproduced.Theresultisacomplex,fullydense,near-net-shapepart(Fig.1).LENShasmanypotentialapplications,includingrapidprototyping,rapidtooling,anddissimilarmetaljoining.Sampleshavebeensuccessfullymanufacturedfromavarietyofmaterialsincludingsteels,stainlesssteels(SS),nickel-basedalloys,refractorymetals,toolsteelalloys,titanium,andintermetalliccompounds.Fabricationofbi-materialjointsaswellasfunctionallygradedmaterialsthroughtheuseofLENShasalsobeendone.Laserprocessinghasthebenefitofconcentratingmuchenergyinthespot,butthedrawbackisitshighcost[7,8].

LENSisatechnologythatisgaininginimportanceandisinearlystagesofcommercialization.Itsstrengthliesintheabilitytofabricatefully-densemetalpartswithgoodmetallurgicalpropertiesatreasonablespeeds.MuchresearchisstillbeingdoneintheU.S.A.laboratories.ThereareonlythreeinstallationsofLENSinEurope:U.K.,France,andSlovenia—aconsortiumofcompaniesandR&DinstitutionswithintheToolmakersclusterofSlovenia.750

POTENTIALOFLENSTECHNOLOGYFigure1.—LENStechnologyinaction.

ThemainadvantagesofLENStechnologyare:1)Fabricationofcomplexproducts,novelshapes,hollowstructures,andmaterialgradientsthatarenototherwisefeasible;

2)Efficientapproachthatreducesproductioncostsandshortenstime-to-marketforhigh-valuecomponents;3)Excellentmaterialproperties,possibilitytocombinedifferentmaterials,significantlyreducedmaterialwaste;4)Lowheatinput—lowdistortionandheat-affectedzone.Sincemechanicalpropertiesaredependentuponthemicrostructureofthematerial,whichinturnisafunctionofthethermalhistoryofsolidification,anunderstandingofthethermalbehaviorofthefabricatedpartduringtheLENSprocessisofspecialinterest.Unlikeotherlaserprocessingtechniques,LENSuseslowpowerlaserswhichproduceaverysmallheat-affectedzone;

5)DirectmanufacturingfromCADtopart,computer-supportedprocesswithclosedloopforprecisiondepositioncontrol.3.WhereandhowcanLENStechnologybeused?InthispartwewouldliketopresenttheuseofLENStechnologyfortool-makingandmedicalpurposesandpresentitsadvantagesoverconventionalprocessingtechnologiessuchasturning,milling,anddrilling.Thetool-makingindustryproduceshighly-complextoolsneededformanufacturingofproductsinautomotive,aerospace,andotherindustries.OneofthemostpromisingapplicationsforLENSisthemanufacturingofplasticinjectiontoolsanddiecasttooling.LENSenablesbuildingcomplexshapes.Oneofthebiggestproblemswithtoolsisthebuildingofcoolingchannelsthatfollowthecontourofthemoldandcavity.Coolingisextremelyimportantbecauseitcanreducepartcycletimebyincreasingtheremovalofheatfromthemold.Thatenablesmorerapidcoolingofthepart,whichcanbeejectedsooner.Morerapidcoolingofselectedareasofthemoldcanreducepartdistortionandimproveaccuracy.

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LENStechnologyenablesbuildingthesecoolingchannelsinavarietyofextremelysophisticatedshapes.

LENSisahighlytargetedmetaldepositiontechnologythatproducesaveryfineweldbead,exposingthecomponenttofarlessheatthanconventionalmethods.Theresulting“heat-affectedzone”withLENSissmallerandmorecontrolledsothattherepairprocessdoesnotdamagetheunderlyingpart.And,sinceaLENSdepositismuchfinerandmoreprecisethanweldingtechniques,farlessfinishingworkisrequired.ThesuperiormaterialpropertieswithLENSextendcomponentlife,reducinglifecyclecosts.MicroscopystudiesshowtheLENSpartstobefullydensewithnocompositionaldegradation.Mechanicaltestingrevealsoutstandingas-fabricatedmechanicalproperties.Theprocessalsoimprovesdesignflexibilitybyallowingnovelgeometries,structures,andmaterialgradients.

Toolsareoftensubjecttowearinspecificareas.SinceLENSisahighlytargetedsolutionthatcanpreciselyaddmaterialtowornordamagedareaswithminimalheateffectitenablesrepairingofthemostsensitivethin-walledcomponents.TheLENSsystemintegrateswellwithconventionalprocessestocreateuniquehybridmanufacturingsolutions.Forinstance,LENScanbeusedtoenhanceanexistingcomponentbyaddinglayersofwear-resistantmaterialorothersurfacetreatments.

LENStechnologyalsofounditsplaceinmedicine.Withitsfastturnaroundtimesandthedesignfreedomitaffords,LENSisanemergingsolutionformedicaldevicemanufacturing,includingthedevelopment,prototyping,andproductionofspecialtysurgicalinstrumentsandprostheticimplants,suchaship,knee,andspinalprosthetics.Theseproducts,builtwithLENStechnology,havemuchbettercharacteristics,e.g.,thickermaterialstructure,lesscorrosiveness,lessporositywhichleadstomuchsmallerpossibilityofbacterialinfection.Medicalimplantshavetobeextremelyflexibletofitinaspecificpatient.Itisalsoimportantthattheweightoftheseimplantsisassmallaspossiblewhilestillensuringpropermaterialcharacteristics.Thisisthereasonthatthin-walledpartsaredesired.Itisextremelyhard(ifnotimpossible)toproducethin-walledimplantswithconventionaltechnologies;therefore,LENStechnologyisamuchbettersolution.

4.ExperimentwithmedicalTi-implant

Thelastpartofthearticlerepresentsanexampleofamodernmedicalimplant.Generally,medicalimplantproductshavetosatisfystrictrequirementsregardingmaterials,machiningtechnologiesandtheirfunctionality.Theyareregulatedandclassifiedinordertoensuresafetyandeffectivenessinthepatient.AfavoritebiomaterialusedforbiomedicalapplicationsistitaniumalloyTi6Al4Vduetoitscombinationofthemostdesirablecharacteristicsincludingimmunitytocorrosion,biocompatibility,shearstrength,density,andosteointegration.Theexcellentchemicalandcorrosionresistanceoftitaniumistoalargeextentduetothechemicalstabilityofitssolidoxidesurfacelayertoadepthof10nm.Ti6Al4Vis,therefore,oneofthemostwidelyusedtitaniumalloyinindustrialapplications[9,10].

Forthefixationoftheradiusbonehead(caputradii)fracturesintheelbowjointaspecialIntramedullary(IM)

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Figure2.—(a)ImprovedconventionalIMnailwithsieve-likehead;(b)PreliminarydesignofIMnailwithattendanceinstruments.

nailhadbeendeveloped.Thenailprototypeswere

manufacturedwithconventionalandLENStechnology.MaterialusedformachiningoftheIMnailistitaniumalloyTi6Al4Vinclassicalform(bars)forconventionalprocessingtechnologiesandinpowderform(45󰀁mgrainsize)forLENStechnology.Withconventionalmachiningtechnologies(turninganddrilling)wegetafullnailformwithtwolinesoffixationscrewholesontheheadofthenailandtwostabilizingscrewholesinthelowerpartofthenail[Fig.2(a)].Forthisdesignattendanceinstrumentshadtobedeveloped[Fig.2(b)].Duetoincapabilityoffulfillingpredictedbiofunctionalityrequirements,theconventionalpreliminarydesignhadtobechangedandimproved.Thesievelikenailheadformhadbeendeveloped,andcadaverbiofunctionalitytestresultsfulfilledrequireddemands.

ThenailproducedwithLENStechnologyishollow,thin-walled,andwithtwostabilizingscrewholesinthelowerpart.Fixationofthefragmentsofthecaputradiiisdonewithdrillingscrewholesduringthesurgicaloperationtotheheadofthenailcoincidentallyinthebestpossiblewaytogainprimarystabilizationofthefracture.Thisispossiblebecauseofthethinwallsofthenail(1mm)andspeciallydevelopeddrillingtools[Figs.3(a)and(b)].

Figure4.—HardnessofLENSandconventionalIMTinailtroughcross-section.

ConventionalIMnailprototypeshadbeenproducedandtestedintheLaboratoryofCutting(LABOD)attheFacultyofMechanicalEngineering,UniversityofLjubljana.LENSIMnailshadbeenproducedinEMOtool-shopandtestedinLABOD.IMnailprototypesproducedwithbothtechnologies(conventionalandLENStechnology)weretestedwithcomputersimulations(FiniteElementAnalysisorFEM)whichhaveshownbothdesignswillwithstandpredictedforcesactingonthenailinthebone.Foradequatematerialpropertiescomparison,afullIMnailwithLENStechnologyhadbeenbuilt.HardnessinHVofbothprototypesofIMnailthroughcross-sectionispresentedinFig.4.

AsseeninFigs.5(a)and(b)thesizeofcrystalgrainismoreregularandtheorderstructureisbetteratIMnailproducedwithLENStechnology.Fromthis,wecanassumebettermechanicalpropertiesofmaterialproducedwithLENStechnology.ThiswasalsoprovedwithtestsregardinghardnessandbiofunctionalityoftheIMnail.Furthertestsbasedonmicrostructureresearchwillbedoneandpresentedinthefuture.

5.Conclusion

TheIMnailproducedwithLENStechnologyhasmoreadvantagesforpracticalusagethanaconventionaltitaniumIMnail.Itislighterduetoitshollowstructure,easiertoinsert,andtheoperationprocedureislesscomplicated

Figure3.—(a)Cross-sectionofLENSprototypeIMnail;(b)LENSIMnailbeforeandafterfinalfinishingprocess.

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Figure5.—(a)MicrostructureofconventionalTi6Al4V;(b)MicrostructureofLENSTi6Al4V.

withnocomplexattendanceinstrumentsneeded.TheLENSIMnailhasbettermechanicalpropertiesthanconventionaltitaniumIMnail.ThesurfaceoftheLENSIMnailcouldstayroughwhichconsequentlyimprovesitsstabilizationinthebone.AswehaveexpectedLENStechnologyprovidedtwohugeadvantages,i.e.,manufacturingofcomplexshapesthataredifficulttoproducewithconventionaltechnologiesandproducingbettermaterialcharacteristics.WeexpectthatLENStechnologywillhaveasignificantplaceinthetool-makingindustryaswellasinmedicalindustry.

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