EffectofmisalignmentonthecuttingforcesignatureindrillingA.Al-HamdanMechanicalEngineeringDepartment,MutahUniversity,Mutah,Karak,JordanReceived27June2000；accepted2January2002AbstractThispaperpresentsastudywhichinvestigatestheeffectofmisalignmentbetweentheaxesofrotationofdrillandtheworkpieceonthesteady-stateanddynamicoftheaxialcuttingforceandtorque.Anovelmethodologyhasbeenproposedtomeasurethemisalignmentbetweentheaxesofrotationofthedrillandtheworkpiece.Thisusesalaser-basedsystemtomeasurethismisalignment,whereareferencebeamhasbeengeneratedbyalasertube,whichisheldinthechuckofthemachineusingaspecialenclosure.Thelaserbeamiscapturedbyaphotosensorcamerahavingavideocapturecard.Tostudytheeffectofthemisalignment,thestartingbushwasintentionallymisalignedbymovingthepressureheadoverthecarriageusingtheleadscrewofthecrossslide.Keywords:Metalcutting；Drilling；Deep-holemachining；Imageprocessing；Misalignment；Cuttingforces1.IntroductionTherelativepositionandmotionbetweenthetoolandworkpiecemayaffectboththesteady-stateanddynamiccuttingforcesdramatically.Thusitbecomesdifficulttodistinguishbetweenthecuttingsignatureduetothedynamicresponseofthecuttingprocessandthatduetothenoiseoriginatingfromanyinaccuracyinthepositionoftheworkpiecerelativetothecuttingtool.Surprisingly,therehasbeenlittleattentionpaidtothiseffectinpreviousstudies.Someofthescatterinthecuttingforcemeasurementsreportedintheliteraturemaybepartiallyexplainedbythementionedinaccuracy.Thisbecomesparticularlyimpor-tantifanewmodelofchipformationhastobeverifiedbyexperiments.Indeep-holedrilling(BTA),therelativelocationofthetoolandtheworkpieceisdefinedbytherelativelocationoftheaxesofrotationofthetool,workpieceandstartingbushasshowninFig.1.Sakumaetal.13investigatedrun-outindeepholesdrilledunderdifferentmisalignmentconditions.TheauthorskeptchangingbetweengundrillsandBTAdrillswhenrunningexperimentswithdifferentsetups.Thustheworkhasnoclearreferencetoaparticulartypeoftoolortoolgeometry.Furthertothisnoinformationwasprovidedontherigidityoftheboringtheyusedintheexperiments.Intoolrotatingsystemsthemisalignmentofthepilotbushoratoolshanksupportmakesthepathofthetooldeviateandcausestheaxestodeviatefromastraightpath4.Beingaself-guidedmachiningprocess,thestraightnesserrorontheholeaxisisfurtheraffectedbytherigidityofthetoolworkmachinesystem.ThestraightnessoftheholeaxesproducedbyBTAdrillingisusuallymeasuredastherun-outmeasure-mentsareinfluencedbythesettingerrorswhiledrilling,namelyoffsetandnonparallelismofaxesoftoolandwork-piece.Therefore,adifferentapproachisnecessarytostudytheerroronthestraightnessoftheaxis,eliminatingthesettingerrors5.Katsukietal.6studiedtheinfluenceoftheshapeofthecuttingedgeonaxialholedeviationindeepdrilling.Sofar,therehasbeennosystematicstudyoftheoveralleffectofmisalignmentontoolwearandtoolperformance,exceptforthestudyonitseffectonrun-out3.Ingeneral,authorsattributeavarietyofundesirableeffectstomisalign-mentbutmostlyasexperience-basedguesswork.Commonproblemsincludethecuttingedgeflakingorchipping,leadingpadwear,poorsurfacefinish,straightnessandroundness.Also,literaturesourcescitethatmisalignmentrelatedproblemsmayandmaynotbeaccompaniedbyexcessivevibration7.Thesectiontofollowpresentstheexperimentalsetupandtheprocedureusedtomeasurethecuttingforcesindeep-holemachining.Thisencompassestheelementsofthesetupsuchasthemachine,theworkpiecematerial,thecuttingtoolandthedynamometer.Thissectioncoversalsothemeasuringsetupanditscalibration.Thenextsectionpresentstheproposedmethodologyandthespeciallydesignedsetupformisalignmentassurance,whichisfollowedbythecalibrationJournalofMaterialsProcessingTechnology124(2002)8391E-mailaddress:.jo(A.Al-Hamdan).ofthemisalignmentassurancesetup.Thisfollowedbythepresentationanddiscussionoftheexperimentalresults.Thelastsectionoutlinestheconclusionsofthisstudy.2.Cuttingforcesmeasurement2.1.Experimentalsetup1.Machine.Fig.1showsthedrillingmachineinstallationusedintheexperiments.Theinstallationconsistsofadriveunit,apressurehead,aboringbarandthedrillhead.Thestationaryworkpiece-rotatingtoolworkingmethodwasusedintheexperiments.2.Dynamometer.A2-componentpiezo-electricloadwasher(Model9065)wasusedtomeasurethecuttingforces.Thetransducerincorporatestwodisks,eachwitharingofquartzcrystalspreciselyorientedinthecircumferentialandaxialdirections.Theloadwasherwasintegratedintoadynamometertobeheldinthechuck.Basedonthestandardmountingasspecifiedbythesupplier(Kistler),theloadwasherwaspreloadedbytwoflangesto120kN.Atthispreload,therangefortheaxialforcemeasurementswasC020to20kNandtherangefortorquewasfromC0200to200Nm.Fig.1showstheschematicarrangementofcuttingforcemeasurementsetup.Theloadwasherwasconnectedtoachargeamplifier(Kistlermodel5004)andinturntoadual-channelFFTspectrumanalyser(B&KAnalyserType2032).Thesetupwascalibratedstaticallyanddynamically.Thedynamiccalibrationofthedynamometerworkpiecemachinetoolsystemwascarriedouttoavoidmeasuringthevibrationofthetoolinsteadoftheforcefluctuationsanddeterminethefrequencyband,overwhichthedynamometercouldbeusedforreliablemeasurements.Also,thefre-quencyresponsewasmeasuredtodeterminetherangeoffrequenciesofthecuttingforces,whichcouldbemeasuredaccuratelywithoutdistortion.TheloadwasherwithalliedchargepreamplifiersandtheFFTanalyserwascalibratedbyFig.1.Theschematicarrangementofthecuttingforcesexperimentalsetup.84A.Al-Hamdan/JournalofMaterialsProcessingTechnology124(2002)8391strikingthedynamometerwithKistlerhammer(Model912).Toexaminethevalidityofthemeasurement,thecoherencefunctionwascalculatedforthethrustforceandthetorque.2.2.CuttingtoolBTASsystempartionedboringheadsof1in.diameter(Sandvikdesign)wereused.AdetaileddiagraminFig.2showsthedrilldesignandthegeometry.Thecuttingedgeisdividedintothreesections.ThegeometryparametersofthedrillswerecontrolledaccordingtheAmericanNationalStandardB94.50-1975.Eachcuttingedgewasexaminedatmagnificationof20C2forvisualdefectssuchaschiporcracks.2.3.WorkpiecematerialStainlesssteel(AISI303)wasusedasworkpiecematerial.Thecomposition,theelementlimitsandthedeoxidisationpracticewerechosenaccordingtotherequirementsofANSI/ASMEB94.55M-1985andwererequestedfromthesteeldealer.3.MisalignmentmeasurementsetupTheschematicarrangementoftheexperimentalsetuponthedeep-holemachineisshowninFig.3.AphotographoftheexperimentalsetupisshowninFig.4.Alaser-basedmeasurementsystemwasdevelopedtomeasurethemis-alignmentbetweentheaxesofrotationofspindlenoseandthatofthestartingbushofthedeep-holemachine.Areferencelaserbeamwasgeneratedbyalasertube,whichwasheldinthechuckofthemachineusingaspecialenclosure.Thelaserbeamwascapturedbyaphotosensorcamerahavingavideocapturecard.Theoutputimagesweresenttoimageprocessingsoftwaretotrackthelaserbeampositionbyprocessingtheseimages.TheoutputfromtheimageprocessingsoftwareprovidedthepositionoftheFig.2.BTAStoolsofpartionedcuttingedges(Sandvikdesign).A.Al-Hamdan/JournalofMaterialsProcessingTechnology124(2002)839185centroidofthelaserbeamonthephotosensorinacertainpositionalongtheaxisofrotationofthemachine.Themisalignmentswerecalculatedbycomparingtheaveragecentroidofthecapturedimageswhenthephotosensorcameraandstartingbushaxescoincideandwhenthecameraandnosespindleaxiscoincide.Toalignthemachine,thiscentroidhadtobebroughttocoincidewiththezer