Workpiece roundness profile in the frequency domain an application in cylindrical plunge grinding.docx

Workpiece roundness profile in the frequency domain an application in cylindrical plunge grinding.docx

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Workpieceroundnessprofileinthefrequencydomainanapplicationincylindricalplungegrinding

DOI10.1007/s00170-014-5664-3

Workpieceroundnessprofileinthefrequencydomain:

anapplicationincylindricalplungegrinding

AndreD.L.Batako&SiewY.Goh

Received:

21August2013/Accepted:

21January2014/Publishedonline:

14February2014

#Springer-VerlagLondon2014

AbstractIngrinding,mostcontrolstrategiesarebasedonthespindlepowermeasurement,butrecently,acousticemissionhasbeenwidelyusedforwheelwearandgapelimination.Thispaperexploresapotentialuseofacousticemission（AE）todetectworkpiecelobes.ThiswasachievedbysectioningandanalysingtheAEsignalinthefrequencydomain.Forthefirsttime,theprofileofthegroundworkpiecewaspredictedmathematicallyusingkeyfrequenciesextractedfromtheAEsignals.Theresultswerevalidatedagainstactualworkpieceprofilemeasurements.Therelativeshiftofthewaveformedonthesurfaceofthepartwasexpressedusingthewheel-workpiecefrequencyratio.AcomparativestudyshowedthattheworkpieceroundnessprofilecouldbemonitoredinthefrequencydomainusingtheAEsignalduringgrinding.

KeywordsPlungegrinding.Roundness.Waviness.Frequency.Acousticemission

1Introduction

Grindingismostlyusedasthelaststageofamanufacturingprocessforfinefinishing.However,recently,highefficiencydeepgrinding（HEDG）wasintroducedasaprocessthatachieveshighmaterialremovalratesexceeding1,100mm3/mm/s[1–5].Grindingismainlyusedtoachievehighdimen-sionalandgeometricalaccuracy.However,incylindricalplungegrinding,vibrationisakeyprobleminkeepingtighttolerancesandformaccuracy（roundness）ofgroundparts.

Machinetoolsaredesignedandinstalledtohaveminimumvibration（withanti-vibrationpadwhenrequired）.Neverthe-less,ingrinding,theinteractionbetweenthewheelandtheworkpiecegeneratespersistentvibration.Thisleadstovaria-tionoftheforcesactinginthecontactzone,whichinturncausesavariationinthedepthofcutonthegroundworkpiece.Consequently,thiscreateswavinessonthecircumferenceoftheworkpiece.Theengenderedunevenprofileonthework-piecesurfaceleadstoamodulationofthegrindingconditionsofthefollowingsuccessiverotations;thisiscalledworkpieceregenerativeeffect.Thebuildingupofthiseffectcantakeplaceingrindingcycleswithlongerduration.Similareffectsoccuronthegrindingwheelsurface;however,theprocessofthebuildupisslow[6–9].

Itisgenerallydifficulttogetagrindingwheelperfectlybalancedmanually,whichisacceptableforgeneralpurposegrinding.Forprecisiongrinding,automaticdynamicwheelbalancingdevicesareused.Thoughcurrentgrindingma-chineshaveautomaticbalancingsystemstoreducetheout-of-balanceofgrindingwheels,inactualgrinding,forcedvi-brationisstillcausedbythedynamicallyunbalancedgrindingwheels[10].Thisisbecauseanyeccentricityintherotatinggrindingwheelgeneratesavibratorymotion.

Thestiffnessofthewheelspindleandthetailstockalsoaffectsthewheel-workpiece-tailstocksubsystem,whichoscil-latesduetotheinteractionofthewheelwiththeworkpiece.Inpractice,thegeneratedforcevibrationishardtoeliminatecompletely.Thistypeofvibrationhasgreaterinfluenceontheformationoftheworkpieceprofile.Duringthegrindingprocess,theout-of-balanceofthewheelbehavesasasinusoi-dalwaveformthatisimprintedontheworkpiecesurface.This,

asinapreviouscase,leadstothevariationofdepthofcutand

A.D.L.Batako（*）:

S.Y.Goh

AMTReL,TheGeneralEngineeringResearchInstitute,LiverpoolJohnMooresUniversity（LJMU）,ByromStreet,LiverpoolL33AF,UK

e-mail:

******************.uk

createslow-frequencylobesaroundtheworkpiece,andthisisthekeytargetofthestudypresentedhere.

Otherfactorssuchasgrindingparametershavetobetakenintoconsiderationinthestudyofgrindingvibrationbecause

theseaspectsaffectthestabilityoftheprocess.Thisisbecausetheresultingworkpieceprofileisthecombinedeffectofdifferenttypeofvibrationingrinding[7,11].ThestudiescarriedoutbyInasaki,TonouandYonetsushowedthatthegrindingparametershaveastronginfluenceontheamplitudeandgrowthrateoftheworkpieceandwheelregenerativevibration[12].

Theactualmeasurementoftheworkpieceprofileisanintegralpartofthemanufacturingprocessduetotheuncertain-tyinwheelwearandthecomplexityofthegrindingprocess.Contactlessmeasurementandcontactstylussystemsweredevelopedtorecordthevariationsoftheworkpiecesizeandroundness.However,thesetechniquescanbeusedaspost-processcheckingasitislimitedtoaparticularset-upandmustbeusedwithoutthedisturbanceofthecuttingfluidinacleanair-conditionedenvironmentwithstabletemperature[13–16].Intheindustry,randomsamplesfrombatchesareusuallyinspectedafterthegrindingprocess.Anyrejectionofpartsorsometimesbatchesincreasesthemanufacturingtimeandcost.Therefore,itbecomesimportanttodeveloponlinemonitoringsystemstocutdowninspectiontimeandtominimiserejectedpartsingrinding.Someoftheexistingmonitoringsystemsingrindingarebasedonthewheelspindlepower.However,sen-sorssuchasacousticemissionandaccelerometersarealsousedtogatherinformationofthegrindingprocessfordifferentappli-cation.Dornfeldhasgivenacomprehensiveviewoftheappli-cationofacousticemission（AE）sensorsinmanufacturing[17].MostreportedapplicationsofAEingrindingareforgapelim-

ination,touchdressingandthermalburndetection[18–21].

Incylindricalgrindingprocesses,thegeneratedchattervibrationcausesthelossofformanddimensionalaccuracyofgroundworkpieces.Theeffectofvibrationinducestheformationoflobesontheworkpiecesurface,whichareusu-allydetectedusingroundnessmeasurementequipment.High-precisionpartswithtighttoleranceareincreasinglyindemandandshortcycletimesputpressureonmanufacturingprocess-es.Thisleadstotheneedfordevelopingin-processroundnessmonitoringsystemsforcylindricalgrindingprocesses.

Thepotentialofusingacousticemissiontodetecttheformationoflobesonaworkpieceduringacylindricalplungegrindingprocessisinvestigatedinthiswork.Theaimistoextracttheworkpieceroundnessprofilefromtheacousticemissionsignalinthefrequencydomain.Theextractedfre-quenciesarecomparedwithactualmeasurementinfrequencydomain,i.e.harmoniccomponents.Thekeyfrequenciesoftheharmoniccontentareusedtopredicttheexpectedprofileonthegroundpart.

2Thestudyofacousticemissionplungegrinding

AEisanelasticwavethatisgeneratedwhentheworkpieceisundertheloadingactionofthecuttinggritsduetothe

interfacialandinternalfrictionalandstructuralmodification.Thewavegeneratedistransmittedfromthecontactzonethroughthecomponentsofthemachinestructure[22,23].Ingrindingprocesses,themainsourceoftheAEsignalisthemechanicalstressappliedbythewheelontheworkpieceinthegrindingzone[24].Thechippingactionoftheabrasivegritsontheworkpiecesurfacegeneratesamultitudeofacous-ticwaves,whicharetransmittedtothesensorthroughthecentresandthetailstockofmachine.Themachiningconditionisreflectedinthesignalthroughthemagnitudeoftheacousticemission,whichvarieswiththeintensityofthecutting,e.g.rough,mediumorfinegrinding.ThekeyinformationofthemachiningprocessanditsconditionisburiedintheAEsignal.ToextractanyinformationofinterestfromtheAEsignals,itisimportanttoidentifythefrequencybandwidthandstudythesignalindetails.

SusicandGrabecshowedthatintensivechangesofAEsignalrelatetothegrindingcondition,thusthegroundsurfaceroughnesscouldbeestimatedbasedonthemeasuredsignalwithaprofilecorrelationfunction[25].AstrongchattervibrationingrindingisalsoreflectedintherecordedRMSAEsignal.Asvibrationcouldgeneratethewavinessontheworkpiece,hence,theAEsignalwasalsousedtostudytheroundnessprofile[26].Acomprehensivestudyofthechattervibration,wheelsurfaceandworkpiecequalityincylindricalplungegrindingbasedontheAEsignalwascarriedoutrecently[27].

Inroundnessmeasurementsystems,theroundnessofthepartisalsogivenasharmoniccomponents.Generally,thefrequencyspangivenbythemeasurementmachineisoflowfrequency—500Hzandbelow.Thisisbecausetheroundnessprofiledealswiththewavinessbutnotwiththesurfaceroughnessthatisalwaysofhigherfrequency.Fricker[8]andLiandShin[28]alsoindicatedpartsprofileoffrequencybelow300Hz.Partroundnessprofileisexpressedinundula-tionperrevolution.Therefore,lowerfrequencycomponentsaremainlytargetedbythemeasurementequipment,buthigherfrequencycomponentstendstorideontopoflowercarriers.Inmostcases,theprovidedfrequencyprofileisintherangeof300Hz[8,28].Therefore,thisworkstudiestheAEsignalalongthegrindingprocessusingthefastFouriertransform（FFT）withaparticularfocusonfrequenciesbelow300Hz.Thisallowedforadirectcomparisonbetweentheresultsfromthisinvestigationandtheactualroundnessmeasurements.

Figure1illustratestheequipmentusedinthisstudy,where

（a）istheconfigurationofthegrindingmachinewiththelocationofthesensorsand（b）istheroundnessmeasurementmachine.Toimprovesignaltransmission,thecoatingofthetailstockwasremovedfromthelocationofthesensorsasshowninthisfigure.

Duringthisstudy,observationsoftheshapeoftherec