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Damage and dimensional precision on milling carbon fiber-reinforced plastics using design experiments.pdf

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Damage and dimensional precision on milling carbon fiber-reinforced plastics using design experiments.pdf

JournalofMaterialsProcessingTechnology1602005160–167DamageanddimensionalprecisiononmillingcarbonfiberreinforcedplasticsusingdesignexperimentsJ.PauloDavim∗,PedroReisDepartmentofMechanicalEngineering,UniversityofAveiro,CampusSantiago,3810193Aveiro,PortugalReceived24June2002receivedinrevisedform10May2004accepted8June2004AbstractMillingcompositematerialsisarathercomplextaskowingtoitsheterogeneityandthenumberofproblems,suchassurfacedelamination,thatappearduringthemachiningprocess,associatedwiththecharacteristicsofthematerialandthecuttingparameters.Withthepurposeofunderstandingandreducingtheseproblems,thispaperpresentsastudythatevaluatesthecuttingparameterscuttingvelocityandfeedrateunderthesurfaceroughness,anddamageinmillinglaminateplatesofcarbonfiberreinforcedplasticsCFRPs.Aplanofexperiments,basedontheTaguchismethod,wasestablishedconsideringmillingwithprefixedcuttingparametersinanautoclaveCFRPcompositematerial.AnanalysisofvarianceANOVAwasperformedtoinvestigatethecuttingcharacteristicsofCFRPcompositematerialusingcementedcarbideK10endmills.TheobjectivewastoestablishamodelusingmultipleregressionanalysisbetweencuttingvelocityandfeedratewiththesurfaceroughnessanddamageinaCFRPcompositematerial.©2004ElsevierB.V.Allrightsreserved.KeywordsMillingCarbonfiberreinforcedplasticsCFRPsDimensionalprecisionTaguchismethodOrthogonalarraysAnalysisofvarianceANOVA1.Introduction1.1.MillingfiberreinforcedplasticsFRPsMillingisthemachiningoperationmostfrequentlyusedinmanufacturingpartsoffiberreinforcedplastics,becausecomponentsmadeofcompositematerialsarecommonlyproducedbynetshapethatoftenrequiretheremovalofexcessmaterialtocontroltolerances,andmillingisusedasacorrectiveoperationtoproduceawelldefinedandhighqualitysurfaces1.Themachinabilityoffiberreinforcedplasticsisstronglyinfluencedbythetypeoffiberembeddedinthecompositeandbyitsproperties.MechanicalandthermalpropertieshaveanextremelyimportanceonmachiningFRP.Thefiberusedinthecompositeshasagreaterinfluenceintheselectionofcuttingtoolscuttingedgematerialandgeometryandmachiningparameters.Itisfundamentaltoensurethatthetoolselectedissuitableforthematerial.Theknowledgeofcuttingmechanismsisindispensableinviewofcuttingmechanicsandmachinabilityassessmentinmilling1,2.∗Correspondingauthor.Tel.351234370830fax351234370953.Emailaddresspdavimmec.ua.ptJ.P.Davim.CompositematerialssuchascarbonfiberreinforcedplasticsCFRPsmadebyusingcarbonfibersforreinforcingplasticresinmatrices,suchasepoxy,arecharacterisedbyhavingexcellentpropertiesaslightweight,highstrengthandhighstiffness.Thesepropertiesmakethemespeciallyattractiveforaerospaceapplications2.Surfaceroughnessisaparameterthathasagreaterinfluenceondimensionalprecision,performanceofmechanicalpiecesandonproductioncosts.Forthesereasons,researchdevelopmentshavebeencarriedoutwiththepurposeofoptimisingthecuttingconditionstoreachaspecificsurfaceroughness3,4.Forachievingthedesiredqualityofthemachinedsurface,itisnecessarytounderstandthemechanismsofmaterialremoval,thekineticsofmachiningprocessesaffectingtheperformanceofthecuttingtools5.Theworksofanumberofauthors6–12,whenreportingonmillingofFRP,haveshownthatthetypeandorientationofthefiber,cuttingparametersandtoolgeometryhaveanessentialpaperonthemachinability.EverstineandRogers6presentedthefirsttheoreticalworkonthemachiningofFRPsin1971,sincethentheresearchmadeinthisareahasbeenbasedonexperimentalinvestigations.Koplevetal.7,Kaneeda8andPuwandHocheng9concludedthattheprincipalcuttingmechanismscorrelatestronglytofiberarrangementandtoolgeometry.09240136/–seefrontmatter©2004ElsevierB.V.Allrightsreserved.doi10.1016/j.jmatprotec.2004.06.003J.P.Davim,P.Reis/JournalofMaterialsProcessingTechnology1602005160–167161Santhanakrishmanetal.10andRamuluetal.11carriedoutastudyonmachiningofpolymericcompositesandconcludedthatanincreasingofthecuttingspeedleadstoabettersurfacefinish.Hochengetal.12studiedtheeffectofthefiberorientationonthecutquality,cuttingforcesandtoolwearonthemachinability.Insummary,itcanbenoticedthattheworkscarriedoutonthemachinabilityofFRP,arebasicallyrelatedonthewearofcuttingtoolsandthequalityonthesurfaces,asafunctionofthecuttingconditions,thedistributionofstaplefibersinthepolymericmatrixandtheangleofinclinationofstaplefibers.ThecurrentpaperinvestigatestheinfluenceofcuttingparameterscuttingvelocityandfeedrateonthesurfaceroughnessRa,delaminationfactorFd,andinternationaldimensionalprecisionIT,onCFRPcompositematerialusingcementedcarbideendmills,withthepurposetoestablishaempiricalrelationshipbetweencuttingparametersVandfandsurfaceroughnessRaanddelaminationfactorFd.1.2.AutoclaveprocessTheautoclaveprocessiswidelyusedtoproducehighperformancelaminatesusuallywithfibersreinforcedepoxysystems.Compositematerialsmanufacturedbyautoclaveareparticularlyimportantforaerospaceapplications.Thisprocessusesapressurisedvesseltoapplypressureandheattobothpartsthathavebeensealedinavacuumbag.Nextitcanbeseentheseveralstagesofthisprocess.Onthefirststage,theprepregcarbonfiber–epoxymaterialiscarefullylaidoutonatabletoensurethatfiberorientationmeetsthedesignrequirement,wheretheprepregmaterialconsistsofunidirectionallongcarbonfibersinapartiallycuredepoxymatrix.Onthesecondstage,piecesoftheprepregmaterialarecutoutandplacedontopofeachotheronashapedtooltoformalaminate.ThelayerscouldbeplacedindifferentdirectionstoproducethedesiredFig.1.LaminateplateCFRPcompositematerialproducedbyautoclavewithafiberorientationof0/90◦.strengthpatternsincethehigheststrengthofeachlayerisindirectionparalleltothefibers.Aftertherequirednumberoflayershasbeenproperlyplaced,thetoolingandtheattachedlaminatearevacuumbagged,forremovingtheentrappedairfromthelaminatedpart.Finally,thevacuumbagandthetoolingisputintoanautoclaveforthefinalcuringoftheepoxyresin.Afterremovedfromtheautoclave,thecompositematerialisreadyforfurtherfinishingoperations2,13.2.Experimentalprocedure2.1.MethodandmaterialsInordertoreachtheobjectiveofthisexperimentalwork,mainlytheestablishmentofthecorrelationsbetweencuttingparametersVandfandsurfaceroughnessRaanddelaminationfactorFd,machiningissueswereperformedunderdifferentcuttingconditionsontheCFRPcompositematerial.Thecompositematerialusedinthetestsepoxymatrixreinforcedwith55ofcarbonfiber,suppliedbyINEGI,wasproducedbyautoclavewithafiberorientationof0/90◦,ascanbeobservedinFig.1.Theexperimentshavebeencarriedoutinalaminateplate,madeupwith16alternatinglayersoffiberswith4mmofthickness,usingtwocementedcarbideK10endmills,presentedinFig.2,with6mmofdiameter.Bothcementedcarbideendmills,twofluteR216.3206030AC10P1020andsixfluteCCTGSRD0635,weremanufacturedaccordingtoISO.Thetwofluteendmillpresentsthefollowinggeometryahelixangleof30◦,arakeangleof10◦30prime,aclearanceangleof9◦andaflutelengthof10mm.Thesixfluteendmillpresentsaneutralhelixand20mmofflutelength.ThedepthofthecutonCFRPcompositematerialwas2mm.AmillingmachineLC11/2VSFirstwith2.2kWspindlepowerandamaximumspindlespeedof2500rpmwasusedtoperformtheexperiments.162J.P.Davim,P.Reis/JournalofMaterialsProcessingTechnology1602005160–167Fig.2.aTwoflutecementedcarbideK10endmill,bsixflutecementedcarbideK10endmill.Fig.3.Fixationofthelaminateplateinthepressofjawofthemillingmachine.ThefixationofthecompositematerialplatewasmadeasobservedinFig.3,tomakesurethatvibrationsanddisplacementdidnotexist.ThesurfaceroughnesswasevaluatedaccordingtoISO4287/1withaHommeltesterT1000profilometer,ascanbeobservedinFig.4.Foreachtestfivemeasurementsweremadeovermillingsurfaces,accordingtoFig.5.Consideringthenumberofmeasurementstobecarriedout,aprogrammabletechniquewasused,bypreviouslyselectingaroughnessprofile,thecutoff0.8mmandtheroughnessevaluatorparameterRaaccordingtoISO.DataacquisitionsweremadethroughproFig.4.SurfaceroughnessevaluatedwithaHommeltesterT1000profilometer.Fig.5.Diagramofthefivemeasurementsthatweremadeforeachpalpationovermillingsurfaces.filometer,byinterfaceRS232toPCusingthesoftwareHommeltesterTurboDatawin.Thedamagecausedonthecompositematerialwasmeasuredwithashopmicroscope,MitutoyoTM500®,with30magnificationand1H9262mresolution.2.2.PlanofexperimentsTaguchismethodhasbeenwidelyusedinengineeringanalysisandconsistsofaplanofexperimentswiththeobjectiveofacquiringdatainacontrolledway,inordertoobtaininformationaboutthebehaviourofagivenprocess.TheTaguchismethodfortwofactorsatthreelevelswasusedfortheelaborationoftheplanofexperiments.Table1indicatesthefactorsstudiedandtheassignmentofthecorrespondinglevels.Bylevelsismeantthevaluestakenbythefactors.TheorthogonalarrayL924,wasselectedasshowninTable2,whichhasninerowscorrespondingtothenumberoftests8degreesoffreedomwithtwocolumnsatthreelevels.Thefactorsandtheinteractionsareassignedtothecolumns.Theplanofexperimentswasmadeofninetestsarrayrows,wherethefirstcolumnwasassignedtothecuttingvelocityVandthesecondcolumntothefeedratefandTable1AssignmentofthelevelstothefactorsLevelCuttingvelocityVm/minFeedratefmm/min128200238410347860J.P.Davim,P.Reis/JournalofMaterialsProcessingTechnology1602005160–167163Table2OrthogonalarrayL924ofTaguchi15L924test1234111112122231333421235223162312731328321393321LineargraphL92415.theremainingwereassignedtotheinteractions.TheoutputsstudiedweresurfaceroughnessRaanddelaminationfactorFd,intheCFRPcompositematerial.ThetreatmentoftheexperimentalresultswasbasedontheanalysisaverageandtheanalysisofvarianceANOVA14–17.Ananalysisofvarianceofthedatawiththesurfaceroughnessanddelaminationfactor,ontheCFRPcompositematerialwasdonewiththeobjectiveofanalysingtheinfluenceofthecuttingvelocity,andthefeedrateonthetotalvarianceoftheresults.3.ResultsanddiscussionTheresultsofmillingtestsallowedtheevaluationoftheCFRPcompositematerialmanufacturedbyautoclave,usingtwocementedcarbideK10endmills.ThemachinabilitywasevaluatedbysurfaceroughnessRa,delaminationfactorFdandinternationaldimensionalprecisionIT.3.1.InfluenceofthecuttingparametersonthesurfaceroughnessThesurfaceroughnessRawasevaluatedwithaHommeltesterT1000profilometer,accordingtoISO4287/1.Tables3and4showtheresultsofthesurfaceroughnessRaasafunctionofthecuttingparameters,forbothendmills,twoandsixflute,respectively.Table3ValuesofRaasafunctionofthecuttingparameters,forthetwofluteendmillTestVm/minfmm/minTest1Test2Test3Test4Test5SurfaceroughnessRaaH9262m1282001.201.351.301.291.551.342284101.501.901.651.301.801.633288602.782.862.742.772.802.794382000.951.251.121.151.321.165384101.551.451.651.601.501.556388602.302.452.482.501.902.327472001.151.251.201.231.101.198474101.501.341.151.281.171.299478601.901.582.141.632.001.90aAverageoffivemeasurements.InFig.6,theevolutionofthesurfaceroughnessRacanbeseenwiththefeedrate,forthedifferentcuttingspeedvalues.FromFig.6,itcanberealisedthatthevalueofRaincreaseswithfeedrateanddecreaseswiththecuttingvelocity,i.e.withahighercuttingvelocityandalowerfeedrateitispossibleobtainabettersurfacefinish.Itcanalsobeobservedthatthetwofluteendmillprovidesabettersurfacethanthesixfluteendmill.Table5showstheresultsoftheanalysisofvariancewiththesurfaceroughnessRaforbothendmills.Thisanalysiswascarriedoutforalevelofsignificanceof5,i.e.foralevelofconfidenceof95.ThelastcolumnofthepreviouslyshowntablesindicatesthepercentageofcontributionPofeachfactoronthetotalvariationindicatingthen,thedegreeofinfluenceontheresult.FromTable5,itcanberealisedthatthefeedratefactorP77.5,havestatisticalandphysicalsignificanceontheobtainedsurfaceroughnessRa,fortwofluteendmill.ThefactorcuttingvelocityP9.5doesnotpresentstatisticalandphysicalsignificanceonthesurfaceroughness,becauseTestFFα5andPpercentageofcontributionerrorassociated.NoticethattheerrorassociatedtothetableANOVAfortheRawasapproximately1.7.ThevalueofinternationaldimensionalprecisionITcanbeobtainedbythefollowingempiricalequationaccordingtoUNIISO3963/2IT∼30Ra1RabeingthesurfaceroughnessinH9262m.Table6showstheresultsofthedimensionalprecisionIT,obtainedbyEq.1,asafunctionofthecuttingparameters.

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