1、JournalofMaterialsProcessingTechnology84(1998)4755Alaserbeammachining(LBM)databaseforthecuttingofceramictileI/Black*/S/A/J/Livingstone/K/L/ChuaDepartmentofMechanicalandChemicalEngineering/Heriot-WattUni6ersity/Riccarton/EdinburghEH144AS/UKReceived13December1997AbstractThispapercoversthecuttingofcomm
2、ercially-availableceramictilesusingaCO2lasercuttingmachine/withtheobjectofproducingalaserbeammachining(LBM)databasethatcontainstheessentialparameterinformationfortheirsuccessfulprocessing/Variouslasercuttingparameterswereinvestigatedthatwouldgenerateacutinceramictilewhichrequiredminimalpost-treatmen
3、t/Theeffectsofvariousshieldgases/ofmulti-passcuttingandofunderwatercuttingwerealsoexamined/1998ElsevierScienceS/A/Allrightsreserved/Keywords/CO2；Lasercutting；Ceramicmaterials；Advancedmanufacturingprocesses1/IntroductionandbackgroundManualmethodsofcuttingceramictilesareverysimilartothatforglass/i/e/s
4、cribingthematerialswithtungsten-carbidetippedcutter/followedbytheapplica-tionofabendingmomentalongthescribedlinetoinitiatecontrolledfracture/However/manualtech-niquesarelimitedtostraight-linecuttingandrelativelylarge-radiuscuts/Internalandundercutprofilesarenearlyimpossibletoproducewithscoringalone(
5、withthepossibleexceptionofinternalcircles)；moresophis-ticatedmethodshavingtobeappliedtoachievetheseprofiles/Traditionally/diamond-saw/hydrodynamic(waterjet)orultrasonicmachiningareusedtocreatecomplexgeometriesinceramictiles/buttheseprocessesareverytimeconsumingandexpensive/Forexample/typicaldiamond-
6、sawcuttingspeedsareintheorderof20mmmin11/whileultrasonicdrillingofAl2O3takesover30sperhole2/ThemostcriticalfactorarisingfromuseofaCO2lasertocutceramictilesiscrackdamage/whichisessentiallycausedbyahightemperaturegradientwithintheceramicsubstrateduringthecuttingprocess/Thesecracksreducethestrengthanda
7、resourcesforcriticalcrackgrowth/whichmayresultinpartialorcompletefailureofthetilesubstrate3/Thusareduc-tionofprocess-inducedcrackformationisparamountfortherealisticcommercialuseoflaserstocutceramictiles/2/LasercuttingparametersLasermachiningofanymaterialisacomplexprocessinvolvingmanydifferentparamet
8、ersthatwhichallneedtoworkinconsorttoproduceaqualitymachiningoperation4/parameterssuchas/(i)laserpowerinput；(ii)focalsetting；(iii)assistgastypeandpressure；(iv)nozzleconfiguration；(v)workpiecethickness；and(vi)optophysicalproperties/Previousresearchwithintheauthorsdepartment1/5/6hasalsodemonstratedthec
9、riticalityoftheaboveparametersinefficientlasercutting/2/1/LaserpowerLaserpowerdependsonthetypeoflaserused/Fortheworkreportedinthispaper/aFerrantiMF400CNClasercutterwasemployed/ratedatapoweroutputof400W/However/duetoupgrading/themaximumbeampowerachievablewasbetween520and*Correspondingauthor/Fax/44131
10、4513129；e-mail/i/blackhw/ac/uk0924-0136/98/$-seefrontmatter1998ElsevierScienceS/A/Allrightsreserved/PIIS0924-0136(98)00078-8I/Blacketal//JournalofMaterialsProcessingTechnology84(1998)475548530Wincontinuouswave(CW)cuttingmode/Thelaseralsohadtheabilitytoworkinpulsemode(PM)andsuper-pulsemode(SPM；Fig/1)
11、/Todeterminetheequivalentpoweroutputduringpulsingoperation/apowerversespulsingchartwasusedinconjunctionwiththefollowingbasicequation9/PrPl/Psf1/(PlPr)Althoughthelasercuttercouldoperatebetweenfre-quenciesof50and5000Hz/avalueof500Hzwasrecommendedinpreviouswork1/5/Sincethissettingprovedtobesuccessful/o
12、nlylimitedinvestigationintootherfrequencieswascarriedout(at250Hz/750and100Hz)/2/2/CuttingspeedTheCNCtableusedwiththeFerrantiMF400lasercutterhadamaximumfeedrateof10000mmmin1/Previouswork6indicatedthatfeedratesabove6000mmmin1provedtobeunstableforanystandardisedtesting/Theoptimumcuttingspeedvariedwitht
13、hepowersettingand/moreimportantly/withthethicknessoftheworkpiece/2/3/ShieldgastypeandpressureCompressedair/argon/nitrogenandoxygenwereusedasshieldgasesduringcutting/withpmax/4bar/Differentshieldgaseswereusedtoexaminedtheireffectoncutqualityafterprocessing/sincetheshieldgasnotonlycoolsandcutedgesandr
14、emovesmoltenmaterial/butalsogeneratesachemicalreactionwiththesub-stratematerial7/Theresultsofthischemicalreactiondifferforeachtypeofshieldgasused/Fortestpurposespwasvariedinstepsof0/5barfrom1to2/5bar/theninstepsof0/2barfrom2/6bartothemaximumattainablegaspressure/2/4/NozzleconfigurationThenozzlediame
15、tercontributesdirectlytothemaxi-mumachievablegaspressureandhencetothemassflowrateofthegaswasimportantfortheeconomicsofcutting/especiallywhenusingcylindersofargonandnitrogen/Onlycircularprofilesforthenozzleexitswereavailable(0/6mm5Ns520mm)/butthisuniformnozzleexitgeometryallowedcuttinginanydirection/
16、2/5/NozzleheightandfocalpositioningTheheightatwhichthenozzlewassetwasgovernedbythepositionofthefocalpoint/TheFerrantiMF400lasercutteronlypossessedalongfocallengthof110Fig/1/Cuttingmodes/mm(originallyashortfocallengthof46mmwasavailablebeforeupgrading)andthislengthcouldbealteredby95mm/Ifthenozzleheigh
17、twasincorrectlysetthebeamwouldclipthenozzleandreducetheequivalentpoweroutputtotheworkpiece6/Forthebulkofthetestingthefocalheightwassetsothefocalpointwasonthejob/i/e/onthetopsurfaceoftheworkpiece/Thisconditionobviouslygovernedtheposi-tionofthenozzleabovetheworkpiece/3/ExperimentalprocedureSixtypesofS
18、i/Al2O3-basedceramictileswereexam-ined(Table1)/originatingfromdifferentcountries/Notethatthecompositionofthetilesvaried/asdidthethickness/butallpossessedasurfaceglazeandinthecaseofthe7/5/8/6and9/2mmSpanishtilestheglazewasdoublelayered/3/1/Set-upprocedureSincetherewasaneedforstandardtestingcondi-tion
19、s/thefollowingprocedurewasimplementedbeforethestartoftesting/(i)thebeampowerwasvalidatedtospecification/i/e/520530Wdevelopedatfullpower(CW)/althoughthisdroppedtoaround50WafterTable1Typesofceramictileusedts(mm)TiletypeBodycolour3/7BrazilianWhite4/7WhitePeruvianLightredItalian5/2SpanishRed5/74Spanish7
20、/5RedRedSpanish8/69/2RedSpanishI/Blacketal//JournalofMaterialsProcessingTechnology84(1998)475549about1hoftesting；(ii)thenozzleandthefocallenswerecheckedtoensurethattheywereingoodcondi-tion/i/e/cleanandundamaged；(iii)theshieldgaspressureregulatorandshieldgastankswereturnedontopreventdamagetothefocall
21、ens；(iv)thelaserbeamwascentredwithinthenozzleusingasquaretest/alowerenergyinputinPMbeingusedtocutasquareonamildsteel/thesparkingdensitythatresultedfromcuttingbeingcheckedtoseeifitwasequallydistributedaboutthecutline；and(v)thefocalpointwassetforitsdesiredpositioning/i/e/onthejob/3/2/TestingAstraight-
22、linetest(SLT)wasusedtoevaluatethevariablelaserparametersforfullthrough-cutting(FTC)/Angularcuttingwasconfiguredtoinvestigatehowthematerialreactedduringcuttingoftightgeome-try/Circulartestingandsquaretestingweredevisedtodeterminetheeffectsresultingfromcuttingvariousgeometries/TheSLTallowedforthecombi
23、nedtestingoftwoseparateparametersononetestpiece/uponcompletiontheresultsbeingpresentautomaticallyinacuttingmatrixintheformoftheresultingcuts/PandVarethemostimportantlaserparameters/astheydictatetheamountofenergyinputperunitlengthofcut/thereforetheywerepairedfortheSLT/aswerepandNSwhichgovernthemassfl
24、owrateoftheshieldgas/FortheP/Vtestruns/thepowerwasheldconstantwhilethecuttingspeedwasincreasedalongthecut(Fig/2(a)/ThelengthofcutatconstantcuttingspeedhadtobeofsufficientmagnitudetoaccommodatetheaccelerationordecelerationoftheCNCtablebetweenfeedchanges/previouswork6indicatedthat50mmwasadequate/Inter
25、pretingtheresultswasmadeeasierduetotheirtabularformat/withthecuttingmatrixshowingclearlyanytrendsorpatternsoccurringduetothechangesinparametersettings/TheSLTalsoal-lowedalargenumberofcutstobecarriedoutoverashorttime-frame/Thisprovedadvantageous/asthelasertendedtodriftfromitsinitialsettingswithtime/P
26、recautionshadtotakentoavoidlocalisedheatinginthetilefromcontinuouscloseproximitycutting/asachangeintilebodytemperaturewouldinvalidateanyresultingdata/Initially/a20mmseparationbetweencutswasusedandthisprovedsufficient/Inordertostudyhowclosethecutscouldbemadetoeachother/theseparationbetweencutswasredu
27、cedbyincrementsof2mmfromaninitial20mmspacing/DuringtheSLTtheotherlaserparametershadtobeheldconstant6/ForPversusV/fwasheldat500HzwithNS1/2mmandp3bar/Thebeamfocalpointremainedonthejob/TheresultsfromtheP/VcuttingmatrixdeterminedthefixedvaluesforthecuttingspeedandpulsesettingsforthesucceedingSLT/FortheN
28、S/pFig/2/Testingconfiguration/(a)straight-linetesting；(b)angulartesting；(c)circulartesting；(d)squaretesting/cuttingmatrix/thenozzlesizeremainedconstantalongthex-axis(refertoFig/2(a)whilepwasincreasedinstepsof0/2barfrom2barinthey-axis(thecutseparationremainedconstantat20mm)/Anewmatrixwascreatedsubseq
29、uentlyforeachnozzlesize/Angulartesting(Fig/2(b)wasusedtoinvestigatehowthecutmaterialreactedtosustainedexposurefromthelaserbeamduringthemachiningoftightgeometries(i/e/whereseveralcutsaremadeincloseproximitytoeachother)/TheproximitytestmentionedforSLTdetermineshowcloseparallellinescanbecuttoeachother/
30、whereasangulartestingisusedtodeter-minehowthecuttingofacuteangleseffectsthecutquality/Theanglescutfromaworkpiecewerereducedfrom45to10andthecorrespondingsurfacefinishquality(SFQ)wasnoted/I/Blacketal//JournalofMaterialsProcessingTechnology84(1998)475550Table2Multi-passcuttingparametersPlCuttingmodePsN
31、o/ofpassesLastcutCW60FTC9000100SPMFTC100Table3GradingofSFQGrading1Nocrackinginsurfaceglaze/solidsharpcutedgeMinimalglazecracking(WcB2mm)withslight2lossofsharpnessincutedgeMediumcracking(2mmBWcB4mm)andslight3damagetounglazedtilesubstrateSignificantdamagetoglazecoating(Wc6mm)/4heavydamagetounglazedsub
32、stratecausingflakingintheglazedsurface5Sameas4butwiththeformationofcracksinthetilesmainbodyleadingtostructuralfailureinapartofthetile(usuallyattheendofacutorwithin8mmofthetileedge)/Therearetworeasonsforconductingsquareandcirculartesting(Fig/2(c)and(d)/first/todeterminetheoptimummethodoflaser-beamint
33、roductiontointernalcutprofiles；andsecondly/todetermineiftherewasanylimitationinthedimensionofthesizeofsquareorholecut/Ifnotcorrectlyintroduced/thelaserbeamwouldcauseaninternally-cutprofiletofailatthepointofintroduction/duetothebriefbutexcessivethermalgradientinducedfromcutting(i/e/thermalshock)/Ther
34、efore/utilisingmethodsofbeamintroduc-tion/suchastrepanning/ontoaprofileenabledcom-plexgeometriestobeinvestigated/Whatalsobecameapparentduringtestingwastheimportanceofthepositionofbeamextractionfromthecutprofileandthepositionofthebeamstartingpointrelativetothegeometry/i/e/whetheritwasatacorneroronast
35、raightedge/3/3/Multi-passandunderwatercuttingMulti-passcuttingwasbegunwithalowpower(P100W)laserbeam/Thefirstpassproducedawelldefinedblindkerfinthesubstrate/followedbyasecondpasstocutdeeperandsoon/Theprocesswasrepeateduntilthekerfwasabout20mmdeepandthenthelaserpowerwasswitchedto500WanddothefinalFTC/T
36、heobjectiveofmulti-passcuttingwastoreducether-maloverloadbyuseoflessinputenergyperunitlength/TheparametersusedinthistestaregiveninTable2/Underwatercuttingwasconductedwiththeobjectiveofreducingtheinfluenceofheataroundthecutareaandalsotoexaminedtheeffectoncutqualitythroughacceleratedheatdissipationusi
37、ngwater8/Thece-ramictilewasplacedunderwaterandthenozzlewasalsodippedinwater/theshieldgaspressurepreventinganywaterfromenteringthenozzlejetchamber/4/CutqualityMaterialproperties/laserparametersandworkpiecegeometryhaveasignificanteffectonthefinalresultofthelasercuttingprocess/Cutqualityisessentiallych
38、ar-acterisedbysurfaceroughnessanddrossheight/whereascracklengthdictatesthestrengthreductioninthesubstrate(Fig/3)/TheoverallSFQattheglazesurfacewasclassifiedaccordingtothegradingscalegiveninTable3/Therefore/thequalityofthecutsurfaceandedgeweremeasuredwithrespectedto/(i)surfaceroughness；(ii)surfacefinishand；(iii)drossadherence/Fig/3/Qualitycriteriaforthelasercuttingofceramictiles/
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