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Ceramic sponge Abrasive Waterjet (AWJ) precision cutting through a temporary filling procedure Viganò, F.; Cristiani, C.; Annoni, M. This is a post-peer-review, pre-copyedit version of an article published in JOURNAL OF MANUFACTURING PROCESSES. The final authenticated version is available online at: http://dx.doi.org/10.1016/j.jmapro.2017.05.014 This content is provided under CC BY-NC-ND 4.0 license

1

CeramicspongeAbrasiveWaterjet(AWJ)precisioncutting

throughatemporaryfillingprocedure

F.Viganò1,C.Cristiani2,M.Annoni1

1MechanicalEngineeringDepartment,PolitecnicodiMilano,Milano,Italy

2Chemistry,MaterialandChemicalEngineeringDepartment“GiulioNatta”(CMIC),

PolitecnicodiMilano,Milano,Italy

Correspondingauthor:

FrancescoViganò

Tel.:3343012952

E-mail:francesco.vigano@polimi.it

ABSTRACT

Ceramicspongemachiningafterfiringisagreatissue,requiringspecialtoolsandprocedures

becauseofthematerialpeculiarmacro-structureanditsintrinsicbrittleness.Thisstudy

approachestheproblembyexploitingtheAbrasiveWaterjettechnology(AWJ)andshowing

itspotentialasaflexibletool.Nowadays,AWJiscomingupasanalternativetootherceramic

manufacturingprocessessuchasGrinding,UltrasonicMachiningandLaserMachining.The

influenceofatemporaryporefillingagent,infiltratedinthealreadysinteredsponge,is

evaluatedanditseffectonthejetcoherenceisinvestigatedthroughbothmodellingand

experimentalapproaches.Themostsuitableprocessparametersareassessedinorderto

reducethemainAWJdefectsintheseconditions,settingthefeedrate(vf)at150mm/minona

35mmthick30PPI(poresperinch)ceramicspongeonaconventionalcuttingequipment.

2

Theoverallkerfdivergenceisthereforereduceddowntolessthan1°thankstothefilling

procedureandthenitiscompensatedbyexploitinga5-axiscuttingcentre.Defectsare

measured,usingbothconventionalandadhoctools(e.g.CMM,grazinglightsurface

inspectionanddigitalimageanalysis).NothermalorchemicalactionsareappliedbytheAWJ

cuttingprocessandthenegligibleforcesexertedonthestrutspreservetheirintegrity.Acase

studygeometryismachined,fulfillingtighttolerancesof0.1mmonaØ10mmceramic

spongecylinderovera15mmthickness.Acomplex-shapedcomponentiscuton35mmthick

sponge.

KEYWORDS

AbrasiveWaterjet;Ceramicspongecutting;Temporaryspongefilling;Defectcompensation.

1.INTRODUCTION

Highqualitymachiningofceramicmaterialsisanincreasinglyrelevantindustrialissueand

AbrasiveWaterJet(AWJ)isbecomingawell-establishedtechnologyforsolidceramiccutting,

asconfirmedbyAbdel-Rahman[1].ThisstudyisaimedatdemonstratingtheAWJprocess

potentialalsoincuttingnear-net-shapeceramicspongecomponents.

Afillingagentistemporarilyinfiltratedinthesinteredspongeporesinordertopreservethe

ceramicspongestructureintegrityfrombeingdamagedbythenaturaljetdivergence.This

novelapproachcanbeappliedtoallkindofceramicormetalspongesandisdifferentfrom

pre-sinteringinfiltration,whichisusefulinothercases,e.g.toenhancethespongestructure

geometryduringfiringlikeinGriel[2]andLietAl.[3],ortocreatecompositematerialsby

permanentinfiltrationasreportedbyChaberaetAl.[4]andRashedetAl.[5].

3

Theinteractionsbetweenthejetandthefilledspongearetestedinthispaperonsimple

geometriesandtransferredtomorecomplexcasestudies,wheretighttolerancesarerequired

byfunctionalpurposes.

1.1.CeramicspongesandPSMmethod

AccordingtoSchefflerandColombo[6],ceramicspongesareirregularmonolithicnetwork

structurescharacterizedbyopencells.

Severalprocessesexisttofabricateceramicsponges,includingtheuseofpre-formingagents,

partialsintering,templatemethodsandgel-casting,asreportedbyLiuetal.[7].Aceramic

spongeobtainedbypolymericspongereplicationmethod(PSM)isusedinthepresentstudy.

Inthismethod,patentedin1963asreportedinBreznyandGreen[8],apolyvinylchloride

(PVC)spongetemplateisimmersedintheceramicslurryin“green”state.Itissuccessively

driedandfiredlikemostoftheceramicartefacts,burningoutthepolymerstructure.

TwomaindefectsusuallyoccurinceramicspongesobtainedbyconventionalPSM:the

possibilitytoleaveeitheraholeoracarbonaceousresidueatthecentreofeachstrut,causing

cracksformationandpropagation(Figure1),andthecelldeformation,causinginconsistent

behavioursduringthemachiningoperations.

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Figure1TriangularvoidsinsidethestrutscausedbythePVCcombustioninthe30PPI(pores

perinch)YZAselectedmaterial.

1.2.Ceramicmaterialsmachiningtechnologies

Custom-shapedcomponentsmadeofsolidceramicsandceramicspongesareneededfor

specificapplications.Sinceceramicadditivemanufacturingisatitsveryearlydays,asincase

ofSongetal.[9],itisoftennecessarytoobtainthecomponentshapethroughamachining

operationaftersintering.Themaincandidateprocessesarelistedhere:

• grindingwithdiamond-coatedtools,asreportedbyMalkinandHwuan[10]and

Marinescuetal.[11];

• ultrasonicmachining(USM)androtaryultrasonicmachining(RUM),usingabrasive

slurriesandultrasonicfrequencyvibratingtools,asreportedbyLeeandChan[12]and

bySpuretal.[13];

• laserassistedmachining,locallymeltingthetargetmaterial,whichisthenremovedby

gasflowsormetaltools,asreportedbyMarinescu[14]andKalyanasundarametal.

[15].

Allofthesetechniquescanbesuccessfullyappliedtosolidceramicworkpieces,eveninthe

casetheyexertasignificantmechanicalaction.

Nevertheless,ceramicspongesaredelicatenetworkssincetheircompressivestrengthranges

from2.60to23.07MPaandtheirbendingstrengthrangesfrom1.20to11.10MPa,according

toNoretal[16].

GrindingisthetechnologyclosesttoAWJamongtheoneslistedbefore.MalkinandHwuan

[10]discussedductileandbrittlemodegrindingandincreasedthegrindingwheelspeedupto

178m/storeducetheoverallnormalforcepergrit.ThisprincipleisenhancedbyAWJ,where

theactualabrasiveparticlespeedcanbethreetimesgreater(upto550m/s,seeSection2.3).

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Therefore,thesingleceramicstrutisexposedtoalowerstress,thuswithstandingthejet

actionwithoutcollapsing.

2.AWJ-TARGETEDCERAMICSPONGECHARACTERISTICSDISCUSSION

Alocalisedmaterialremovalactionwithoutstresspropagationisneeded.AWJtechnology

alreadydemonstrateditsdelicatecuttingactionevenonthinglassandbrittlematerials

accordingtoAnnonietal.[17]andHayMohammadJafar[18].

2.1.YZAceramicspongecharacteristics

Theceramicspongeselectedforthisstudyisa35mmthickSELEETylarXFYZA(Yttria

stabilizedZirconia-Alumina),characterizedbyaPPI(poresperinch)indexequalto30.This

sizewellrepresentsthecharacteristicrangeofceramicspongesusedascatalystsupports

(TwiggandRichardson[19]).Table1detailsthechemicalcompositionandotherfunctional

characteristicsofthematerialselectedforthestudy.

Table1Maincharacteristicsoftheceramicspongeselectedforthestudy.

Ceramicspongetype SELEE

TylarXFYZA

Chemicalcomposition Y2O3/CaO/ZrO2/Al2O3

2.5%/2.5%/61%/34%

TypicalworkingtemperatureT[°C] 1550

Cellsize[PPI] 30

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2.2.TypicalAWJdefectsandeffectsonceramicsponge

AWJ-cutcomponentsareaffectedbythreemaingeometricaldefects:kerfwaviness,kerftaper

andjetlag.Inmostsolidceramics,afeedrate(vf)reductionplaysapositiveroleondefects

andincreasesthedepthofcutasconfirmedbythemodelsofWang[20].

Nevertheless,vfcausesconflictingeffectsonceramicspongescuttingdefects,ashighlightedin

Table2.

Table2EffectofvfreductiononthetypicalAWJdefectswhenmachiningdifferentmaterials.

Effectofvfreduction Solidmaterial Sponge

Kerfwaviness Better Better

Kerftaper Better Worst

Jetlag Better Better

2.3.AWJbehaviourincuttingceramicsponge“as-is”

Inasaki[21]describedthebrittlebehaviourofadvancedceramicsinmachining,especiallyin

grinding,basedonthesameabrasion-erosionphenomenaasinAWJcutting.Aparticlehitting

theworkpiecesurfacewithanimpactanglecloseto90°wouldbreaktheceramicspongestrut

bridgewithoutsignificantdeformation.Theabrasiveparticlevelocitywascalculatedas550

m/saccordingtoAnnonietAl.[22],TazibtetAl.[23]andtheCFDsimulationsbyWang[24].

Consideringthishighimpactspeedandthelowmassofaparticle(6.5E-6g/particlefor#80

meshGarnetabrasive),asingleabrasivegraincanonlybreakthestruttip,without

transferringthestresstotheentirestrutduetoitslowinertia.ThetestcutshowninFigure2

highlightsthatthejetcanerodethematerialatlowvfuntilreplicatingthejetfreeshape,while

theresultingkerfwallisnotstraightathighvf.

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Figure2Actualjetshapeandtestspecimenforthe“as-is”cuttingexperimentation(Table3

reportstheAWJconstantprocessparametersappliedinthecurrentstudy).

Table3ConstantAWJprocessparametersappliedinthecurrentstudy.

OrificesØ[mm] Primary:0.33

Focusing:1.02

Waterpressure[MPa] 380

Abrasivetypeandsize Garnet,#80mesh

Abrasiveflowrate[g/min] 350

StandOffDistance[mm] 3

Workpiecethickness[mm] 35

Thisbehaviourcanbeduetothelargedensitydifferencebetweenthesolidceramicstrutsand

theemptypores.Whenpassingthroughapore,thejetlosesitscoherenceanddiverges

assumingalesspredictablebehaviour.

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3.CERAMICSPONGEANDFILLEDCERAMICSPONGECUTTINGCOMPARISON

Several2Dand3Dgeometricalmodelsforreticulatedmaterialsareproposedinliterature.

Maitietal.[25]discussedthefracturemechanismsofbrittlecellularsolids,distinguishing

betweencrackextensionthroughbendingfailureandtensilefailureofthecellstrutsina2D

representation.A3DmodellingapproachwasdiscussedbyJangetal.[26]forpolyurethane

andaluminiumfoams,startingfromtheKelvincellrepresentation,discussedbyThomson

[27],andaimingatmodellingspongestrutsassheardeformablebeams.

Inthisstudy,asimplerequivalentstructureisusedtorepresentfilledceramicsponges,being

cutwhenafillingagentsubstitutesairinsidethespongepores(Section3.2).

3.1.Ceramicspongestructureasamulti-layermaterial

Theoriginalspongestructureisconvertedintoanequivalentmulti-layerstructure,

preservingtheratiobetweensolidmaterialandemptyporealongthejetaxis.Thissimplified

structureallowsapplyingtheconclusionsofthestudiesonAWJcuttingoflayeredmaterials

discussedbyHashish[28].

AX-rayComputedTomography(CT)analysisisperformed,inspectingtheceramicsponge

internalgeometriesasmadebyWallensteinetal.[29]todistinguishthesolidceramicfroma

fluidflow.Theanalysisof1500CTslicesrevealedthatalongthejetaxisdirectionthesolid

ceramic/emptyporeratiois3/17,theaveragestrutthicknessis0.396mmandtheaverage

strutnumberon35mmthickworkpieceis14(Figure3).

9

Figure3X-rayCTimageon20mmthickspecimen(duetomicro-CTdetectorcharacteristics)

andceramicspongeequivalentmulti-layerstructureon35mm.

3.2.Jetbehaviourinfilledceramicsponges

Thejetiswellconfinedwhenpassingthroughthesolidceramicstrut,butitcandivergewhen

itcrossesanemptypore.

Amoredensefillingmaterialisexploitedtoreplaceairandpreservethejetcoherence.The

fillingagentshouldeffectivelyfillthecells,butitshouldbealsoeasy-to-removewithout

leavinganyresidual.Inaddition,itmustnotbechemicallyreactivewiththebasematerial.For

thisreason,EthyleneVinylAcetate(EVA)istestedasfillingagent.Akerfshapecomparison

betweenceramicsponge“as-is”(Figure4,left)andsolidEVA(Figure4,middle)ispresented

toevaluatetheseparatematerialsbehaviourbeforestudyingtheeffectoftheirunion(Figure

4,right).

10

Figure4Comparisonamong“as-is”,solidEVAandEVA-filledceramicspongecutting

(constantprocessparametersreportedinTable3).

Asuperpositioneffectoccursinthefilledspecimencase.TheEVAfillingcounteractsthejet

divergence,thusreducingtheoveralldefectsandfavouringthekerfshaperegularity.

Figure5reportsthedivergenceangletrendofthe“as-is”andEVA-filledcuttingconditions

showninFigure4inthevfrangefrom100to700mm/min.

Thispreliminarycomparison,demonstratingtheEVA-fillingeffectiveness,isfollowedby

thoroughexperimentalplansforwaviness(Section5.1),kerftaper(Section5.2)andjetlag

(Section5.3)reduction.

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Figure5Kerfshapedivergencecomparisonbetween“as-is”andEVA-filledceramicsponge

cutting.

4.CERAMICSPONGETEMPORARYFILLINGPROCEDURE

4.1.Fillingagentselection

DetailsaboutthefillingmaterialsarereportedinTable4.

Table4Maincharacteristicsofthematerialscutbythejetinthestudy.

Fillingmaterial Chemicalcomposition Density

[kg/m3]

Meltingtemperature

T[°C]

SolidYZAceramic Y2O3/CaO/ZrO2/Al2O3

2.5%/2.5%/61%/34%

5060 2000

EVA (C2H4)n(C4H6O2)m 870 120

EVAischaracterisedbyameltingtemperaturethatishigherthanthetemperaturegenerated

bythejetfriction,thusmakingitsufficientlyresistanttopreservethecutwallintegrity.

4.2.Temporaryfillingprocedureassessment

TheceramicspongeworkpieceisimmersedinmeltedEVAuntilallthetrappedairexits

(Figure6)andthenitiscooleddown.

12

Figure6EVAfillingprocedureresults.Somecellsareleftunfilledduetoahastyfilling

procedure(A),whilegoodresultsareobtainedcarefullyperformingtheprocedure(B).

AspecificremovalprocedureisdeterminedtoevacuateEVAfromthefinishedpartusinghot

oil(270°C)toremoveEVAandthencoldacetonetoremovethelastoiltraces.

Athermo-gravimetrictestprovesthatonlyfewEVAtracesremainonthepartafterthe

describedtreatment(1.5%specimenweightlossat450°C,whichcorrespondstotheEVA

degradationtemperature).Inanycase,acalcinationprocessisperformedinthecommon

practiceimmediatelybeforeusingtheparts,thereforeremovingthelastnon-ceramic

residuals.

5.CUTTINGPARAMETERSSELECTIONANDDEFECTCOMPENSATION

ThetypicalAWJdefectslistedinSection2.2aremeasuredinthisstudybymeansofsuitable

proceduresdescribedinthisSection.

5.1Kerfwavinessmeasurementandreduction

Kerfbottomwavinessisstronglyinfluencedbytheceramicspongestrutsrandompositions.

Therefore,anytoolpathcompensationswouldnotbeeffectiveandtheonlywaytoreduce

13

thisdefectisthroughanappropriatevfselection.Kerfbottomwavinessismeasuredbyimage

processing(Figure7).

Figure7EVA-filledspecimenbottomview(A)(vf=100÷900mm/min)andprocessedimage

(B).

Thesinglegrooveimageisdividedin15sub-areas,alocalreferencesystemisattributedto

eachsub-areaandthecharacteristicgeometricquantitiesareinspected(Figure8):

• Tiisthenominaljettrajectory,whereiisthegroovenumber,fromT1toT9;

• XiYjisthelocalreferencesystemdefinedforeachsub-area,wheretheoriginisputon

Tiathalfthesub-areaheight(XirangesfromX1toX9andYjrangesfromY1toY15);

• Cijisthesub-areacentroid,calculatedasthearithmeticalmeanofthepositionofeach

pixelbelongingtotheselectedsubarea;

• xiandyjarethedistancesbetweenthelocalreferencesystemorigin(XiYj)andthe

centroid(Cij).

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Figure8Representationofthegeometricalanalysisappliedtothespecimenbottomsurface.

Thetwodistancecomponentsxiandyjrepresentthegrooveshaperegularityandtherefore

theyareassumedastheprimarycuttingqualityindicators.

Figure9Scatterplotofxiandyiateachvflevel.

Figure10Scatterplotofxiandyistandarddeviationateachvflevel.

15

Figures9and10showthatthebottomkerfirregularityincreaseswithvfinalldirections.

Moreover,thisbehaviourisclearlysignificantintheXdirection.Thedefectistwoordersof

magnitudegreater(Figure9,left)andlesspredictable(Figure10,left)inthisdirectionthanin

Ydirection.Thereforeonlythelowervflevelsmaybechosenandthelimitvfwillbesetat150

mm/mincombiningthisresultswiththeonescomingfromthefollowingSection5.2.

5.2Kerftapermeasurementandcompensation

Theaveragewidthofeachsub-areaiscalculatedbyadedicatedroutineandthenallthewidth

valuesbelongingtothesamegrooveareaveraged.Thisprocedureiscarriedoutbothonthe

topandonthebottomsurfaces,thusobtainingthetopandbottomwidths(WtopandWbot).

Equation(1)byAnnoniandMonno[30]isusedtocalculatethekerftapervalue.

Kerftaper=|Wtop-Wbot|/2 (1)

TheresultsareplottedinFigure11.

Figure11Intervalplotforthekerftaperateachvflevel,obtainedfromadedicated

experimentalplaninthe50-450mm/minvfrangewiththeconstantprocessparametersin

Table3.

16

ThewavinessqualityweakeningeffectdescribedinSection5.1increasesthekerftapervalues

dispersionandmakesitnecessarytolimitvftoamaximumof150mm/min.Thekerftaperis

thencompensatedbytiltingthejet.

Hoogstrate[31]appliedthedefectcompensationstrategybymanagingsimplegeometrical

parametersasthe5-axiscuttingheadtiltangles.TheuseofCAD-CAMtoolsenablesthenew

machinestoapplycompensationstrategiesevenincaseofcurvedgeometries,asreportedby

Westkämperetal.[32].Severalotherstudiesconcerningcircularpartscompensationare

published,liketheonesbyMatsui[33]andHlaváč[34].

Acutmadeatvf=150mm/mingeneratesa0.3mmtaperon35mmthickspecimens,which

canbeeasilycompensatedbytiltingthecuttingheadby0.47°towardsthescraponaplane

normaltothefeeddirection.

5.3Jetlagmeasurementandcompensation

Agrazinglighttechniqueisusedtorevealthejetbendingeffectsonthesurface(Figure12).

Figure12Jetlagmeasurementdefinition.XrandYrdefinethereferencesystem.

17

Differentlyfromwhatnormallyobservedinsolidmetals,thestriationsbecomestraight

segmentsinthiscase.Theinclinationiswellvisibleandconstantfromthejetentrance.

ThejetlagregressionEquation(2)istherefore:

jetlag[mm]=0.485+0.00348vf (2)

Thisequationisvalidon35mmthickspongeforvfvaluesrangingfrom50to450mm/min

andforthespecificmaterial.Itreturnsthejetlagasthejetinletandoutletcoordinate

differencealongthecuttingdirection.Atthemaximumvfallowedtoavoidwaviness(150

mm/min,accordingtoSection5.1),thejetlagisequalto1.007mm.Thisdefectis

compensatedbytiltingforwardthecuttingheadby1.63°alongthefeeddirection,according

tothegeometricmodelsreferencedinSection5.2[31-34].

5.4.Defectcompensationverification

Dedicatedspecimenswerecutaccordingtoaprofilemadeofanarcandtwoparallelwalls

(Figure13A)toverifythecompensationeffectiveness.

Figure13Compensationapproachverification.Specimensketch(A)andCMMmeasurement

representation(B).

18

ThespecimensaremeasuredbyaZeissPrismoHTGCMM.Thedesignedgeometryallows

verifyingthecompensationeffectiveness(Figure13B).

TheCMManalysisoutcomepointsoutthat:

• thewavinessisreducedatitsminimumanditisconstantalongtheentirethickness

(straightprofilesarebetweentwoparallelplanes0.05mmfarfromeachother);

• thetapervalueisreducedaccordingtothetolerancesrequiredbythecase-study

(Section6),withanerrorlowerthan0.07mmonthespecimenthickness(parallelism)

andonthearcradiusateachheight(top,middleandbottom)on35mmthick

specimens;

• thejetlagiswellreduced,asthe90°cornershaveanetshape.

6.CASESTUDY

AcasestudyfortestingthedevelopedcuttingprocedureisprovidedbytheChemistry,

MaterialandChemicalEngineeringDepartmentofPolitecnicodiMilano.Therequired

cylindersmustbestackedinachemicalreactorwithinternaldiameterequaltoØ10±0.02

mm,thereforethecomponentgeometryisdefinedasshowninFigure14.Thecylinder

diameterupperlimitisthemostimportantfunctionaltolerance,thereforeitisverified

(Section6.3)topreventthecylinderfromgettingstuckinthepipe.Thelowerdiametermust

notbesosmalltoavoidfluidleakagebecauseofalargeclearancebetweenpipeandcylinder.

19

Figure14Casestudygeometry(dimensionsinmillimetres).Sincethematerialisporous,the

dimensionsrefertothecircumscribedgeometricalentities.

6.1.Machiningstrategy

Theaimofthiscasestudyisobtainingafinishedpart,avoidingtheusualAWJjunctions

betweenthemachinedcomponentandthebasematerial.Thereforetheconventional

machiningpathismodifiedasshowninFigure15.Anad-hocfixturingsystemwasdesigned

forthespecifictask,sustainingthemachinedcomponentfromthebottom.

Figure15Modifiedmachiningpathfortheentrance-exitdefectsreduction.Disthecircular

trajectorydiameter,adjustedaccordingtotheactualjetdiameter.

ThecirculartrajectorydiameterDwasautomaticallysetbytheCAD-CAMsoftwareto

compensateforthejetdiameter.vfwassetat150mm/mintoreducethewavinesseffects.

Thejettiltangleswerecalculatedbythetapercompensationapproach(Section5.2)andby

thejetlagcompensationapproach(Section5.3).

6.2.Dimensionalverification

Thepartswerefunctionallyverifiedbymeansofapass-gaugeobtainedasa15mmthick

aluminiumplatewhereaØ9.95mmholewascarriedout.

20

Thepartscutwithoutapplyingthecompensationapproachdidnotmeetthedefined

geometricalconstraintsbecauseoftheirconicity(Figure16).

Figure16Casestudypartmachinedwithoutandwiththeproposedcompensationapproach.

6.3.Complexpartcuttingonhighthickness

Achallengingpartgeometrywasselectedtotestthecapabilityofthedevelopedcutting

procedure.Astar,characterizedbybothsharpedgesandobtuseangles,wasmachinedonthe

35mmthickfilledceramicspongeusedforthecurrentexperimentation(Figure17).

21

Figure17Demonstrativestaron35mmthickceramicspongebeforeandafterfillingagent

removal.

Theresultissatisfying.Infact,itisdifficulttodistinguishtheupperandbottomsurfacesasa

proofofthegoodperformanceofthecompensationapproach.Afterthefillingagentremoval,

thefragilesharpedgesofthestartipsareeffectivelypreserved(Figure17,frontview).

7CONCLUSIONS

ThisstudydemonstratesthecapabilityofAWJtechnologytomachineceramicsponges

producinghighprecisionparts.Thisresultisobtainedthankstothedevelopmentofa

temporaryfillingprocedure.TheeffectivenessoftheAWJcuttingperformancesonfilled

ceramicspongesisshownbycasestudiescharacterizedbytighttolerancesandhard-to-

machinegeometricalfeatures.

Theproposedprocessparameters(vf=150mm/min,P=380MPa)allowobtainingprecise

parts,thuscomplyingwithtightdimensionalandgeometrictolerancesandfulfillingthe

functionalneeds.Aconventional5-axisAWJcuttingsystemissuitablefornear-net-shape

22

ceramicspongepartscutting,usingtheproperfillingproceduretopreservethefragile

structureintegrity.

Fromthepartproductionpointofview,theexperimentationisnowbeingextendedtofiner

PPIceramicsponges,morecomplexgeometriesandadvancedhandlingsystemsfor3D

cuttingandshaping.

TheapplicationfieldoftheAWJtechnologyonceramicspongeprocessingwillthereforebe

widened,gettingtheaccesstoenergeticandbiomedicalapplications.

8ACKNOWLEDGEMENTS

TheauthorswishtothanktheWJ_Labstaff,especiallyManuelePredaandGiacomoDidoni,for

theinnovativeideasprovidedforthisstudyandRiccardoBalzarotti,forhisexpertiseinthe

fieldofcatalyticprocessesandequipment.

TheauthorsaregratefultoStefanoPetròandAMALALaboratory(Milano)fortheCTanalysis,

andtoAlessandraPighi,ValerioMussiandMassimoGoletti,MUSPConsortium(Piacenza),for

theimageanalysis.

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26

LISTOFFIGURES

Figure1TriangularvoidsinsidethestrutscausedbythePVCcombustioninthe30PPI(Pores

PerInch)YZAselectedmaterial.

Figure2Actualjetimageandtestspecimenforthecutting“as-is”experimentation(AWJfixed

processparametersinTable3).

Figure330PPIYZAceramicspongeComputedTomographyanalysis(pictureofoneslice)

andequivalentmultilayerstructure(dimensionsinmillimetres).

Figure4Comparisonamong“as-is”ceramicsponge,solidEVAandEVA-filledceramicsponge

cutting(fixedmachiningparametersinTable3).

Figure5Kerfshapedivergencecomparisonbetween“as-is”andEVA-filledceramicsponge

cutting.A3rdgradepolynomialisusedtofitthedata.

Figure6EVAfillingprocedureresults.Somecellsareleftunfilledduetoahastyfilling

procedure(A),whilegoodresultsareobtainedcarefullyperformingtheprocedure(B).

Figure7EVA-filledspecimenbottomview(A)(vf=100÷900mm/min)andprocessedimage

(B).

Figure8Representationofthesoftwareanalysisappliedtothespecimenbottomsurface.Xiis

thelocalgrooveaxisalongXdirection.Yjisthelocalsub-areaaxisalongYdirection.

Figure9ScatterplotofCijXdistance(0isthecuttingtrajectory)andCijYdistance(0isthe

middleheightofeachsub-area)fromthelocalreferencesystemateachvflevel.

Figure10ScatterplotofCijXdistanceandCijYdistancestandarddeviationateachvflevel.

Figure11Intervalplotforkerftaperateachvflevel,obtainedfromadedicatedexperimental

planinthe50-450mm/minvfrange.

Figure12Jetlagmeasurementdefinition.XrandYrdefinethereferencesystem.

27

Figure13Compensationapproachverification.Specimensketch(A)andCMMmeasurement

representation(B).

Figure14Casestudygeometry(dimensionsinmillimetres).Sincethematerialisporous,the

dimensionsrefertothecircumscribedgeometricalentities.

Figure15Modifiedmachiningpathfortheentrance-exitdefectsreduction.Disthecircular

trajectorydiameter,tobetunedaccordingtheactualjetdiameter,tunedbythemachine

accordingtotheactualjetdiameter.

Figure16Casestudypartmachinedwithoutandwiththecompensationapproach.

Figure17Demonstrativestaron35mmthickceramicspongebeforeandafterfillingagent

removal.

LISTOFTABLES

Table1Maincharacteristicsoftheceramicspongeselectedforthestudy.

Table2EffectofvfreductiononthetypicalAWJdefectswhenmachiningdifferentmaterials.

Table3ConstantAWJprocessparametersappliedinthecurrentstudy.

Table4Maincharacteristicsofthematerialscutbythejetinthestudy.