Burr and Cap Formation by Orbital Drilling of Alum

BurrandCapFormationbyOrbitalDrillingofAluminumE.BrinksmeierandS.FangmannAbstractInorbitaldrillingthetool(specialendmill)movesrelativetotheworkpieceonahelicalcourse.Becauseofthethreedimensionaltoolpathandthesuperimposedrotarycuttingmotionacomplexmachiningmotionresultswhichdeterminesthecontactconditionsofthetool.Intheaircraftindustrythisprocessisusedforcuttingcompositematerials(CFRP/Aluminum)withautomateddrillandrivetmachines,forexampleinthemanufacturingofflaptracksandverticaltailplanes.Akeyproblemintheindustrialman-ufacturingofclosedstructuresisthecapandtheburrforma-tionontheboreexitside.Allcapsandchipsmustbeabletoremovebyvacuum,inadditionaminimumburrheightisrequired.Theobjectiveofthisstudyistodescribetheeffectsoforbitaldrillingoncapandburrformationintheexitcom-positematerial,primedcladaluminum2024.Theinfluenceoncapandburrformationwithdifferenttoolgeometries,dif-ferentcoatings,differentcuttingparameters,toolwearandminimumquantitylubricationwereexamined.KeywordsOrbitaldrilling·Burrformation·Capformation1IntroductionCapandburrformationcangenerategreatproblemsinthemanufacturingofclosedstructures,e.g.,flaptracksintheair-craftindustry,becauseacontaminationoftheinternalspacewithcapsandchipsisnotacceptable.Inthiscasethereistheriskofcorrosionandelectricbreakdown[1].Ifitisnotpossibletodrillwithsmallcapsandburrs,twomorework-ingstepsintheassemblyarenecessaryfortheremovaloftheburrandthecleaningoftheclosedstructure.ThisrequiresaE.Brinksmeier,S.Fangmann()FoundationInstituteforMaterialsScience,BadgasteinerStr.3,28359Bremen,Germanye-mail:[e-mail]:[2].Formerinvestigationsshow,thatburrformationisacomplexinteractionofvariousfactors.Primarily,burrforma-tiondependsonthethreefactors:tool,workpieceandprocessparameters,whichcanbesubdividedfurther[3].InFig.1themaininfluencesoncapandburrformationfortheorbitaldrillingprocessareshown.Betweentheinfluencestherearemanyinteractions,however.Ifthereisnoidealprimer,coat-ingorworkpiecematerialused,thetoolwearandmanyotherresultingparametersarehardtoreproduceandthusarenotconstant.Thereforeitisimpossibletoreproduceacapandaburrtoonehundredpercent.Forcapandburrformationonlytendenciescanbepredictedsofar[2–8].Asanalternativetoconventionaldrilling,orbitaldrillingoffersmanyadvantages.Thekinematicsoforbitaldrillingallowdifferentworkingstepsfortheproductionofdifferentboreholegeometrieswithonetool.Orbitaldrillingcanopti-mizethedrillingprocessindifferentforms.Cylindricalholescanbedrilledindependentofthetooldiameterandwith-outchangingthetool.Thismakesitpossibletodrillcom-plextaperedholesandperformfinishingoperationsusingthesamecylindricaltoolandsettings.Anothersignificantadvantageoftheorbitaldrillingprocessisthediametervari-abilitywithouttoolchange.Thisfactoffersthepossibilityforadynamiccorrectionoftheborediameterduringthedrillingprocess.Thiscanbeusedforexample,forthecom-ToolGeometryMaterialCoatingWearWorkpieceMaterialYieldstressTemperaturePrimerCoatingProcessparameterCuttingspeedDepthsettingperorbitalpathFeedvelocityaxialandtangentialLubricationCoolingInfluencesonthecapandburrformationinorbitaldrillingFig.1Influencingfactorsoncapandburrformation[2,3]31J.C.Aurich,D.Dornfeld(eds.),Burrs–Analysis,ControlandRemoval,DOI10.1007/978-3-642-00568-8_4,©Springer-VerlagBerlinHeidelberg201032E.BrinksmeierandS.FangmannFig.2Burrformationontheholeexitsideafterconventionaldrillingofcladprimedaluminum[1]pensationofdiameterdeviationscausedbydifferentmaterialpropertiesinaCFRP/aluminumcompoundstructureoraris-ingtoolwear[9].Moreadvantagesoforbitaldrillingarelit-tledelaminationinCFRP,goodchiptransportationandcut-tingfluidaccessibility.Characteristicsoforbitaldrillingarelowfeedforcesandacuttingedgewhichisnotpermanentlyengaged[10–12].2TargetoftheOrbitalDrillingInvestigationFigure2showsatypicalproblemintheindustrialmanufac-turingofclosedstructuresintheaircraftindustryaftercon-ventionaldrillinginCFRP/aluminum:Thecapandburrfor-mationontheboreexitsideinaluminum.Theobjectiveofthisstudyistoassesstheeffectsoforbitaldrillingoncapandburrformationinaluminum2024T351andprimedcladaluminum2024T351(seeSect.5.1).Toevaluatepossiblewaysforlowburrformationandasmallcapformationontheboreexitsidedifferentinvestigationswithvariedparametersandtoolgeometriesinaborediam-eterrangebetween4.2mmupto6mmhavebeencarriedout.Theexperimentswerecarriedoutintwosteps:Orbitaldrillinginaluminum2024T351andasworsecaseinprimedcladaluminum2024T351.Afurtheraimwastoachievegoodsurfacequalities,maximumtoollifeandhighaccuracyoftheborehole.3OrbitalDrillingInorbitaldrilling(helicaldrill-milling)theboreholeisgen-eratedbyamillingtoolwhichexecutesahelicalpathintotheworkpiece(Fig.3).TheborediameterisadjustedbytheradiusofthehelixpathintheNC-program[10,13,14].InFig.4thefirstcutsofanorbitaldrillingprocessareshown.Picturedisa3mmsolid(cemented)carbidetoolorbitaldrillinga4.2mmborehole.InpositionAthearrow1illustrate