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外文翻译--一个激光束加工(LBM方法)数据库的切割瓷砖 英文版.pdf

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外文翻译--一个激光束加工(LBM方法)数据库的切割瓷砖 英文版.pdf

JournalofMaterialsProcessingTechnology84199847–55AlaserbeammachiningLBMdatabaseforthecuttingofceramictileI.Black,S.A.J.Livingstone,K.L.ChuaDepartmentofMechanicalandChemicalEngineering,HeriotWattUni6ersity,Riccarton,EdinburghEH144AS,UKReceived13December1997AbstractThispapercoversthecuttingofcommerciallyavailableceramictilesusingaCO2lasercuttingmachine,withtheobjectofproducingalaserbeammachiningLBMdatabasethatcontainstheessentialparameterinformationfortheirsuccessfulprocessing.Variouslasercuttingparameterswereinvestigatedthatwouldgenerateacutinceramictilewhichrequiredminimalposttreatment.Theeffectsofvariousshieldgases,ofmultipasscuttingandofunderwatercuttingwerealsoexamined.©1998ElsevierScienceS.A.Allrightsreserved.KeywordsCO2LasercuttingCeramicmaterialsAdvancedmanufacturingprocesses1.IntroductionandbackgroundManualmethodsofcuttingceramictilesareverysimilartothatforglass,i.e.scribingthematerialswithtungstencarbidetippedcutter,followedbytheapplicationofabendingmomentalongthescribedlinetoinitiatecontrolledfracture.However,manualtechniquesarelimitedtostraightlinecuttingandrelativelylargeradiuscuts.Internalandundercutprofilesarenearlyimpossibletoproducewithscoringalonewiththepossibleexceptionofinternalcirclesmoresophisticatedmethodshavingtobeappliedtoachievetheseprofiles.Traditionally,diamondsaw,hydrodynamicwaterjetorultrasonicmachiningareusedtocreatecomplexgeometriesinceramictiles,buttheseprocessesareverytimeconsumingandexpensive.Forexample,typicaldiamondsawcuttingspeedsareintheorderof20mmmin11,whileultrasonicdrillingofAl2O3takesover30sperhole2.ThemostcriticalfactorarisingfromuseofaCO2lasertocutceramictilesiscrackdamage,whichisessentiallycausedbyahightemperaturegradientwithintheceramicsubstrateduringthecuttingprocess.Thesecracksreducethestrengthandaresourcesforcriticalcrackgrowth,whichmayresultinpartialorcompletefailureofthetilesubstrate3.Thusareductionofprocessinducedcrackformationisparamountfortherealisticcommercialuseoflaserstocutceramictiles.2.LasercuttingparametersLasermachiningofanymaterialisacomplexprocessinvolvingmanydifferentparametersthatwhichallneedtoworkinconsorttoproduceaqualitymachiningoperation4,parameterssuchasilaserpowerinputiifocalsettingiiiassistgastypeandpressureivnozzleconfigurationvworkpiecethicknessandvioptophysicalproperties.Previousresearchwithintheauthorsdepartment1,5,6hasalsodemonstratedthecriticalityoftheaboveparametersinefficientlasercutting.2.1.LaserpowerLaserpowerdependsonthetypeoflaserused.Fortheworkreportedinthispaper,aFerrantiMF400CNClasercutterwasemployed,ratedatapoweroutputof400W.However,duetoupgrading,themaximumbeampowerachievablewasbetween520andCorrespondingauthor.Fax441314513129emaili.blackhw.ac.uk0924013698seefrontmatter©1998ElsevierScienceS.A.Allrightsreserved.PIIS0924013698000788I.Blacketal.JournalofMaterialsProcessingTechnology84199847–5548530WincontinuouswaveCWcuttingmode.ThelaseralsohadtheabilitytoworkinpulsemodePMandsuperpulsemodeSPMFig.1.Todeterminetheequivalentpoweroutputduringpulsingoperation,apowerversespulsingchartwasusedinconjunctionwiththefollowingbasicequation9PrPlPsf1PlPrAlthoughthelasercuttercouldoperatebetweenfrequenciesof50and5000Hz,avalueof500Hzwasrecommendedinpreviouswork1,5.Sincethissettingprovedtobesuccessful,onlylimitedinvestigationintootherfrequencieswascarriedoutat250Hz,750and100Hz.2.2.CuttingspeedTheCNCtableusedwiththeFerrantiMF400lasercutterhadamaximumfeedrateof10000mmmin1.Previouswork6indicatedthatfeedratesabove6000mmmin1provedtobeunstableforanystandardisedtesting.Theoptimumcuttingspeedvariedwiththepowersettingand,moreimportantly,withthethicknessoftheworkpiece.2.3.ShieldgastypeandpressureCompressedair,argon,nitrogenandoxygenwereusedasshieldgasesduringcutting,withpmax4bar.Differentshieldgaseswereusedtoexaminedtheireffectoncutqualityafterprocessing,sincetheshieldgasnotonlycoolsandcutedgesandremovesmoltenmaterial,butalsogeneratesachemicalreactionwiththesubstratematerial7.Theresultsofthischemicalreactiondifferforeachtypeofshieldgasused.Fortestpurposespwasvariedinstepsof0.5barfrom1to2.5bar,theninstepsof0.2barfrom2.6bartothemaximumattainablegaspressure.2.4.NozzleconfigurationThenozzlediametercontributesdirectlytothemaximumachievablegaspressureandhencetothemassflowrateofthegaswasimportantfortheeconomicsofcutting,especiallywhenusingcylindersofargonandnitrogen.Onlycircularprofilesforthenozzleexitswereavailable0.6mm5Ns520mm,butthisuniformnozzleexitgeometryallowedcuttinginanydirection.2.5.NozzleheightandfocalpositioningTheheightatwhichthenozzlewassetwasgovernedbythepositionofthefocalpoint.TheFerrantiMF400lasercutteronlypossessedalongfocallengthof110Fig.1.Cuttingmodes.mmoriginallyashortfocallengthof46mmwasavailablebeforeupgradingandthislengthcouldbealteredby95mm.Ifthenozzleheightwasincorrectlysetthebeamwouldclipthenozzleandreducetheequivalentpoweroutputtotheworkpiece6.Forthebulkofthetestingthefocalheightwassetsothefocalpointwasonthejob,i.e.onthetopsurfaceoftheworkpiece.Thisconditionobviouslygovernedthepositionofthenozzleabovetheworkpiece.3.ExperimentalprocedureSixtypesofSiAl2O3basedceramictileswereexaminedTable1,originatingfromdifferentcountries.Notethatthecompositionofthetilesvaried,asdidthethickness,butallpossessedasurfaceglazeandinthecaseofthe7.5,8.6and9.2mmSpanishtilestheglazewasdoublelayered.3.1.SetupprocedureSincetherewasaneedforstandardtestingconditions,thefollowingprocedurewasimplementedbeforethestartoftestingithebeampowerwasvalidatedtospecification,i.e.520–530WdevelopedatfullpowerCW,althoughthisdroppedtoaround50WafterTable1TypesofceramictileusedtsmmTiletypeBodycolour3.7BrazilianWhite4.7WhitePeruvianLightredItalian5.2SpanishRed5.74Spanish7.5RedRedSpanish8.69.2RedSpanishI.Blacketal.JournalofMaterialsProcessingTechnology84199847–5549about1hoftestingiithenozzleandthefocallenswerecheckedtoensurethattheywereingoodcondition,i.e.cleanandundamagediiitheshieldgaspressureregulatorandshieldgastankswereturnedontopreventdamagetothefocallensivthelaserbeamwascentredwithinthenozzleusingasquaretest,alowerenergyinputinPMbeingusedtocutasquareonamildsteel,thesparkingdensitythatresultedfromcuttingbeingcheckedtoseeifitwasequallydistributedaboutthecutlineandvthefocalpointwassetforitsdesiredpositioning,i.e.onthejob.3.2.TestingAstraightlinetestSLTwasusedtoevaluatethevariablelaserparametersforfullthroughcuttingFTC.Angularcuttingwasconfiguredtoinvestigatehowthematerialreactedduringcuttingoftightgeometry.Circulartestingandsquaretestingweredevisedtodeterminetheeffectsresultingfromcuttingvariousgeometries.TheSLTallowedforthecombinedtestingoftwoseparateparametersononetestpiece,uponcompletiontheresultsbeingpresentautomaticallyinacuttingmatrixintheformoftheresultingcuts.PandVarethemostimportantlaserparameters,astheydictatetheamountofenergyinputperunitlengthofcut,thereforetheywerepairedfortheSLT,aswerepandNSwhichgovernthemassflowrateoftheshieldgas.ForthePVtestruns,thepowerwasheldconstantwhilethecuttingspeedwasincreasedalongthecutFig.2a.ThelengthofcutatconstantcuttingspeedhadtobeofsufficientmagnitudetoaccommodatetheaccelerationordecelerationoftheCNCtablebetweenfeedchangespreviouswork6indicatedthat50mmwasadequate.Interpretingtheresultswasmadeeasierduetotheirtabularformat,withthecuttingmatrixshowingclearlyanytrendsorpatternsoccurringduetothechangesinparametersettings.TheSLTalsoallowedalargenumberofcutstobecarriedoutoverashorttimeframe.Thisprovedadvantageous,asthelasertendedtodriftfromitsinitialsettingswithtime.Precautionshadtotakentoavoidlocalisedheatinginthetilefromcontinuouscloseproximitycutting,asachangeintilebodytemperaturewouldinvalidateanyresultingdata.Initially,a20mmseparationbetweencutswasusedandthisprovedsufficient.Inordertostudyhowclosethecutscouldbemadetoeachother,theseparationbetweencutswasreducedbyincrementsof2mmfromaninitial20mmspacing.DuringtheSLTtheotherlaserparametershadtobeheldconstant6.ForPversusV,fwasheldat500HzwithNS1.2mmandp3bar.Thebeamfocalpointremainedonthejob.TheresultsfromthePVcuttingmatrixdeterminedthefixedvaluesforthecuttingspeedandpulsesettingsforthesucceedingSLT.FortheNSpFig.2.Testingconfigurationastraightlinetestingbangulartestingccirculartestingdsquaretesting.cuttingmatrix,thenozzlesizeremainedconstantalongthexaxisrefertoFig.2awhilepwasincreasedinstepsof0.2barfrom2barintheyaxisthecutseparationremainedconstantat20mm.Anewmatrixwascreatedsubsequentlyforeachnozzlesize.AngulartestingFig.2bwasusedtoinvestigatehowthecutmaterialreactedtosustainedexposurefromthelaserbeamduringthemachiningoftightgeometriesi.e.whereseveralcutsaremadeincloseproximitytoeachother.TheproximitytestmentionedforSLTdetermineshowcloseparallellinescanbecuttoeachother,whereasangulartestingisusedtodeterminehowthecuttingofacuteangleseffectsthecutquality.Theanglescutfromaworkpiecewerereducedfrom45°to10°andthecorrespondingsurfacefinishqualitySFQwasnoted.I.Blacketal.JournalofMaterialsProcessingTechnology84199847–5550Table2MultipasscuttingparametersPlCuttingmodePsNo.ofpassesLastcutCW60FTC9000100SPMFTC100Table3GradingofSFQGrading1Nocrackinginsurfaceglaze,solidsharpcutedgeMinimalglazecrackingWcB2mmwithslight2lossofsharpnessincutedgeMediumcracking2mmBWcB4mmandslight3damagetounglazedtilesubstrateSignificantdamagetoglazecoatingWc\6mm,4heavydamagetounglazedsubstratecausingflakingintheglazedsurface5Sameas4butwiththeformationofcracksinthetilesmainbodyleadingtostructuralfailureinapartofthetileusuallyattheendofacutorwithin8mmofthetileedge.TherearetworeasonsforconductingsquareandcirculartestingFig.2canddfirst,todeterminetheoptimummethodoflaserbeamintroductiontointernalcutprofilesandsecondly,todetermineiftherewasanylimitationinthedimensionofthesizeofsquareorholecut.Ifnotcorrectlyintroduced,thelaserbeamwouldcauseaninternallycutprofiletofailatthepointofintroduction,duetothebriefbutexcessivethermalgradientinducedfromcuttingi.e.thermalshock.Therefore,utilisingmethodsofbeamintroduction,suchastrepanning,ontoaprofileenabledcomplexgeometriestobeinvestigated.Whatalsobecameapparentduringtestingwastheimportanceofthepositionofbeamextractionfromthecutprofileandthepositionofthebeamstartingpointrelativetothegeometry,i.e.whetheritwasatacorneroronastraightedge.3.3.MultipassandunderwatercuttingMultipasscuttingwasbegunwithalowpowerP100Wlaserbeam.Thefirstpassproducedawelldefinedblindkerfinthesubstrate,followedbyasecondpasstocutdeeperandsoon.Theprocesswasrepeateduntilthekerfwasabout20mmdeepandthenthelaserpowerwasswitchedto500WanddothefinalFTC.Theobjectiveofmultipasscuttingwastoreducethermaloverloadbyuseoflessinputenergyperunitlength.TheparametersusedinthistestaregiveninTable2.Underwatercuttingwasconductedwiththeobjectiveofreducingtheinfluenceofheataroundthecutareaandalsotoexaminedtheeffectoncutqualitythroughacceleratedheatdissipationusingwater8.Theceramictilewasplacedunderwaterandthenozzlewasalsodippedinwater,theshieldgaspressurepreventinganywaterfromenteringthenozzlejetchamber.4.CutqualityMaterialproperties,laserparametersandworkpiecegeometryhaveasignificanteffectonthefinalresultofthelasercuttingprocess.Cutqualityisessentiallycharacterisedbysurfaceroughnessanddrossheight,whereascracklengthdictatesthestrengthreductioninthesubstrateFig.3.TheoverallSFQattheglazesurfacewasclassifiedaccordingtothegradingscalegiveninTable3.Therefore,thequalityofthecutsurfaceandedgeweremeasuredwithrespectedtoisurfaceroughnessiisurfacefinishandiiidrossadherence.Fig.3.Qualitycriteriaforthelasercuttingofceramictiles.

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