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G.Seligeretal.(eds.),AdvancesinSustainableManufacturing:Proceedingsofthe8thGlobalConference149onSustainableManufacturing,DOI10.1007/978-3-642-20183-7_22,Springer-VerlagBerlinHeidelberg2011MethodologyforHighAccuracyInstallationofSustainableJigsandFixturesJ.Jamshidi,P.G.MaropoulosDepartmentofMechanicalEngineering,UniversityofBath,UKAbstractTheabilitytoaccuratelymeasurethecomponentsofjigsandfixturesduringtheirinstallationdeterminesthestateoftheirprecision,especiallyforlargesizeproductsandapplications.Thismatteriscrucialinmasscustomisationwheresmallbatchesofproductsandcomponentswithhighvarietyindesignaremanufactured.Productqualityshouldbeinharmonywithrapidchangeoverphilosophyascompromisingqualityforspeedisnotforgivableforsensitivecomponentsandassembliessuchasthoseseenintheaerospaceindustry.Itisnecessaryfortheinstallationofthejigsandfixturestobehighlyaccurateinordertominimisetheuseoftolerancebudgetduetovariationsinjigsandfixturepositioning.Majoroverheadcostsforjigsandfixturesparticularlyintheaerospaceindustryledtothedevelopmentoftheconceptofflexibleandreconfigurablejigsandfixtures.Reusabilityofreconfigurablejigsandfixturesmakesthemattractiveforsustainablesolutionsastheircomponentscanbereusedforseveralvariantofaproductorassembly.Themaindrawbacksofthistypeofjigsandfixtureshavebeentheirpooraccuracyandreliability.Inthispaperaccuratepositioningofthekeycomponentsofsustainablejigsandfixturesisinvestigated.Thefactorsaffectingtheperformanceofthejigsandfixturesarereviewedfromtheinstallationstage.Thepaperintroducesamethodologyforminimisinguncertaintiesinpositioningoftheholdsandclampsforflexiblejigsandfixtures.Keywords:SustainableJig,Jiginstallation,CalibrationUncertainty,JigMonitoring,Metrology,ReusableJig1INTRODUCTIONFactorssuchasqualityandreliabilityhavelongconvertedtoimplicitcharacteristicsofthenewproducts.Recentmarkettrendshaveforcedmanufacturingindustriestomovetowardsmasscustomisationintheirproductsandservicerange.Increasedvariationinthedesignofnewproductsisfollowedbyasecondwaveofvariationwithhigheramplitudeatsubassembliesandcomponentlevel.Stateoftheartmanufacturingsystemsandtechnologieshaveprovidedmoreflexibility,enablingdesignerstothinkmorefreely.Forinstancenewlargevolumemeasurementsystems,developedinthepastfewyears,arecapableofmeasuringseveraldecametredistances.Suchtechnologiesfacilitatetheverificationoflargesizecomponentsthatusedtobemanufacturedfromseveralassembledcomponents.Themanufacturingoflargesizeproductsrequiresspecialistjigsandfixturesinorderfortheircomponentstobeheldinthedesiredorientationduringbuildandassembly.Thisrequiresmajoroverheadcostthatcanonlybejustifiedbymassproductioninsomecasesorotherwisethecostoffinishedproductscanbeveryhigh.Thisissuecontradictswiththemarkettrendswherecustomersareconstantlylookingforhighervaluefortheirmoney.Inatypicalproductthevariationintheproductcreatesamoresustainablebusinessasitcanfulfiltheneedsofarelativelylargermarket.Flexibleandreconfigurablejigsandfixturethatcanbeformedindifferentshapestosupportdifferentvariationofproductsisakeysolutionfortheabovechallenges.Theconceptofflexiblejigexistedforseveralyearsintheresearchdomain1.However,theyarenotfullyutilisedtoagreatextentinrealproductionfacilitiesespeciallyforlargesizeproductmanufacturers,suchasaerospace.Thisisduetothechallengesrelatedtotheirinitialinstallation,poorcalibration,andrepeatabilitythatoftenexceedthetolerancerequirement.Themanufacturingofthesejigsandfixturesfromhighqualitykeycomponentsaswellastheirintegrationwithlargevolumemetrologysystemscanreducetheabovelimitations.Thispapercoversmetrologyissuesrelatedtotheinstallationandcalibrationofflexiblejigsandfixturesaswellastheirmonitoringduringservice.2RELATEDWORK2.1ManufacturingandassemblyoflargescalepartsTypicallypriortoprecisionmanufacturingofmechanicalpartsitisessentialtomovetherawmaterialtothemachinebench,proceedwithroughcuttingthenfinealignmentandclamping.Atthisstagethepartisreadyformachiningofitshighprecisionkeyfeatures.However,thisisnotalwayspossibleforlargesizeand/orheavycomponents.Largescaleproductsrefertothosewithcomponentsthatarenoteconomicallypossibletohandleormovearoundinthefactoryforfabricationandassemblypurposes2.Themanufacturingandassemblyprocessesofthesepartsencompassmovementofthemachinesandsystemstothedesiredlocationandorientationwithrespecttotheseparts.Suchpartsarenormallyheldintheirpositionsusinglargesizejigsandfixtures.Ifthesepartsareproducedinsmallbatchsizesthatisthecaseforaerospaceindustries,highoverheadcostperproductwilloccur.Therehavebeenmanyattemptstodesignandmanufacturejigsandfixturessothattheycanholdanumberofvariantsofcomponents3,4.However,thisapproachisnotfeasibleforpartswithsensitiveorkeyfeaturesduetotheirhighaccuracyrequirements.J.Jamshidi,P.G.Maropoulos150Adjustable,reconfigurablejigsandfixturesproducelowerrepeatabilityovertimecomparedtofixedones.Fixedjigshavepermanenttopologyachievedthroughtheirpermanentjointsthatareweldedorriveted.Mechanicalfailureofthesejigsandfixturesforexampleduetofatigueandplasticdeformationisamaincauseofterminatingtheirserviceandsendingthemforrecycling.Withsmallbatchmanufacturingrequirementsitisnowcommontoretireaconformingjigastheirservicelifedependsonthelifeofproducts.Inotherwordssoonaftertheceaseofmanufacturingapartsvariant,theassociatedjigsandfixturesbecomeredundant.Evenifthejigsarestillinworkingorder,theyhavetobescrappedandsentforrecycling.Thismethodbringstheburdenofhighenergyconsumptionforrecycling.Evenforthefixedjigsandfixturesthedriftinthelargesizepartsandjigcanaffecttheaccuracyofalargesizeassembly5.Severalmethodsforanalysingjigrigidityhavebeendeveloped6toevaluatetheimpactofvibrationonlargesizejigs.Inanycaseamoresustainablemanufacturingcanonlybeachievedbyalternativesolutions.Figure1:Typicalcomponentsoflargescalejig(imagecourtesyofElectroimpact/G150TFIX/gallery.asp)Extensiveleadtimetomanufactureisanothermajordrawbackforfixedjigsandfixtures.Thesejigsshouldbeorderedwellinadvanceofanymanufacturingprocesses.Thiscancreateadditionalcomplexityinproductionplanningandproducttimetomarket.Regardlessoftheirtype,largescalejigshaveanumberofcommonelementsincludingonemainframe,oneoranumberofinnerframes,potentiallyoneoranumberofmovingmechanisms,andsmallercomponentssuchasclamps,bushings,pickupsandadjustablescrews(Figure1).2.2FlexiblejigsandfixturesTheconceptofflexiblejigsandfixturesisdevelopedforincreasedsustainability,rapidchangeoveraswellaslowcost.Itisnowpossibletouseofftheshelfmodulesandclampsforjigsandfixturesdesignandassembly.Dependingontherequirementonlyahandfulofspecialisedcomponentsforthejigsandfixturesmightbeneededtobecustomdesignedandmanufactured.Inthisconceptthemajorityofbulkcomponents,jointsattheattachmentsareusedinforaspecificapplication.Oncetheproductdesignvariantisfullymanufactureditisthenpossibletodisassembletheabovecomponentsandreassembletheminanewtopologytosuitethenextdesignvariant.Thiscyclecanberepeatedoveralargenumberoftimesresultinginreducedoverheadcostforjigsandfixtures.Needlesstomentiontheotherfactorssuchasdisassemblytime,resettingtime,operatorstimeshouldbeconsideredforevaluatingtherealcostbenefitofusingthistypeofjigsandfixtures.Thisapproachbestreducesthecostofjigsandfixturesfortheassemblyandcomponentrangesthatarefairlycloseindesign.Dependingonthelevelofvariationsinthecomponentsandthetypeofworkrequiredoneachadifferentpercentageoftheflexiblejigsneedtoberearranged.Thismatteriscrucialtobeconsideredatdesignstageinordertoincreasethebenefitofusingthistypeofjigsandfixtures.Forexample,whenpossible,thelocationand3Dpositioningofpickupsandclampsondifferentvariantsofthecomponentoreventotallydifferentpartsshouldbeincloseproximitytoincreasecompatibilityandinter-changeabilityofsub-systemsofjigsandfixtures.Havingacollectionofthekeycomponentsofthejigscanguaranteetheavailabilityofthedesiredjigsinashorttime.Inadditiontothisthestorageofthejigsrequiredlessspaceasitispossibletodismantleallthemodulesthataretypicallyintheformofscaffoldingandplacethemnexttoeachother.Flexiblejigsarecurrentlyutilisedinsomeoftheautomotivecompanies(Figure2)astheiraccuracylevelissufficientforthissector.DespitetheabovebenefitsthereareClampMainframeInnerframeComponentAdjustableholdsMovingmechanismsMethodologyforHighAccuracyInstallationofSustainableJigsandFixtures151notmanyflexiblejigsinoperationinlargesizemanufacturingfacilitiessuchasaerospacefactories.Accuracyanduncertaintyofpositioningpins,repeatabilityoftheclampsanddriftofthejigstructureareallcontributingtothefactthatthesejigscannotmeetthetolerancerequirementsofthepowergenerationandaerospaceindustries.Thesejigshavehighpotentialsforutilisationintheaboveindustriesoncetheiraccuracyproblemsareresolved.Figure2:Fixturewithreconfigurablecomponentsforautomotiveindustry(imagecourtesyofWittehttp:/www.horst-witte.de/en/)Therehasbeenanumberofnewdevelopmentsinlargevolumemetrologysystemsandtechnologies.Modernlaserbasedmetrologysystemsandtechnologiesarenowcapableofmeasuringlargesizeproductsuptoseveraldecametreswithacceptableaccuracy.Thesesystemscanbeusedtoaccuratelypositionmountingsofthekeycomponentsofthejigduringitsinstallationandinitialsetup.Theinstallationofjigsandfixturestypicallystartsformitsbaseormainframethenlargecomponentsandgraduallytothesmallercomponentssuchaspickupsandclamps.Metrologysystemscanbeusedfortheinstallationofflexiblejigmainframeanditsinnerframestoguaranteethecorrectpositioningofeachandeverycomponent.Table1showsafewoftheselargescalemeasurementsystems.Fortechnologicalreviewofthesesystemssee7.Lasertrackersystemscapableofmeasuringreferencepoints,areamongthemostsuitablemeasurementsystemsforthispurpose.TheinstrumenttracksaSphericallyMountedRetroreflector(SMR)targetthepositionofwhichcanberegisteredinthreedimensionalspace.SMRcanbecontacteddirectlywiththetargetobjecttoprovidegeometricalpositionalinformationorcanbeusedwithinamechanicallyrepeatableSMRnestknownasLasertrackertargetorinshorttargetfromthispointon.Lasertrackerslikeanyothermeasurementinstrumenthavealevelofuncertaintythatneedtobeaccountedforduringthejiginstallationprocess.Alsothelineofsightissuesbetweenthelasertrackeranditstargetpointshouldbeconsideredandifnecessarymultipletrackerpositionsshouldbeused.Inrealmeasurementactivitytheresultmustbeaccompaniedwithastatementofuncertainty.Suchstatementcharacterisesthedispersionofthevaluesthatarereasonablyattributedtothemeasurand8.Thisissueisthesamefortheinstallationandlaterverificationofanyjigorfixture.Thisknowledgeclarifiesthejigcapabilityofagivenpositioningandassemblytask.Inotherworditindicatesifajigcanmeetthetolerancerequirementsforitsrelatedprocesses.2.3ComparisonofjigphilosophiesTherearealargenumberofdifferentshapeanddesignjigsandfixturesindifferentcompaniesforvariousmanufacturingandassemblyapplications.Someofthesejigsandfixturesarereadilyavailableinstandardforms,whilesomearedesignedandmanufacturedspecifictoparticularpartsandtasks.Thelattercanbeveryexpensivebasedonthecomplexityandscaleoftheproducts9.Regardlessofcostandpurposeamanufacturingorassemblyprocesscanbeperformedusingwithnojig,withfixedframejigs,orwithreconfigurableorflexiblejigs.Table2providesacomparisonofthesemethodswiththeirtypicalapplications.Fixedframejigsaretypicallyforheavydutyapplications.Theyaremoresuitableforapplicationswithalargenumberofproductsthatcanrelaxtheoverheadcostofthejig.Thereareseveraladvantagesintheapplicationofflexiblejigsandfixturesforthemanufacturingandassemblyoflargeandcomplexproducts.Inparticularforresearchanddevelopmentwork,aswellasforcaseswherelowvolumeproductsaremanufacturedflexiblejigandfixturecanbeverybeneficial.Inadditiontotimeandmoneysavingbenefitsthepossibilityofhavingaflexiblejiggivesmorefreedomtothedesign,manufacturingandassemblyprocessesduetothelowdirectandrecurrentcostofchangingtheoveralltopologyofthejig.ReconfigurabilityandreusabilityofflexiblejigisamainClampMainframeInnerframeComponentJ.Jamshidi,P.G.Maropoulos152advantageforthistypeofjigcomparedtoconventionaljigs.Thisisparticularlyimportantasitisinlinewiththeindustrydirectionintermsofgreenmanufacturingbyrecyclingcomponentsfromausedsystem,reducingprojectcostswithregardstoexpensesfortoolingofassociateditems.Table1:Examplesoflargevolume/portablemeasurementinstrumentsforjigverificationMeasurementtypeInstrumentAuxiliarycomponentsContactNon-contactImageSMRprobe9LaserTrackerT-probe9LaserRadarSphericaltargets9Targets9PhotogrammetryLightprojection9Laserbasedscanninghead9ArticulatedArmCMMContactprobe93FLEXIBLEJIGINSTALLATIONTheissuesandconcernsthatneedtobeconsideredinthejiginstallationprocedurearedescribedinthissection.Theinstallationofthejigcomponentsintherightpositioncanbeachallengingespeciallywhenthepositioningtolerancesaretights.Flexiblejigsshouldalsobemonitoredinordertoexploitandcomparetheirrigiditywiththatoftheconventionalones.Stagebystagemeasurementinstructionforthejiginstallationbasedontheresultsofaninitialjigsetupinthesimulationsoftwareenvironmentandpracticalexperimentofalargesizejigwithdimensionsof5mx4mx3misgiveninagenericdescription.Thisisregardlessofwhetherthejigisinfirsttimeinstallationoritisachangeofanexistingjigtopologyintoanewshape,forholdingadifferentcomponent.Dependingonthecomplexityatypicallargesizejighasbetweenthreetofivelevelsofframes.Apartfromthebaselevelwithnormallyonemainframe,ateachleveltherecanbeoneorseveralframes.Theseframesareinterrelatedwithreferencetothejigdatuminordertofacilitatethepositioningandfunctionalityrequired.Inanautomated,fixedplatform,roboticsystemscarryoutseveraltaskssuchaspartpositioning,machiningandassembly.Therobotworkingdatumthereforeislinkedwiththeworkingframeofthejig.Carefulconsiderationofjigdatumingstrategyanditssubsequentinstallationcansecureachievingthedesiredtolerance.3.1MeasurementassistedflexiblejiginstallationThereareseveralstagesfortheinstallationofflexiblejigsthatcanbecarriedoutinfirstsimulationandthenrealworld.Theuseofsimulationexercisecanreducethenumberofpotentialerrorsandreworkduringthisprocess.Theprocessofmeasurementassistedinstallationissimilartotrackingobjectstopositionthatiscommonforlargesizeassemblies.Inthisapproachthecomponentsofthejigareroughlypositioned,within1mmtolerancefromthetargetposition,atfirst.Thenwhenallofthejigcomponentsareattachedintotheirdesignatedpositions,within0.1mmto0.15mmtolerance,theyaretightenedusingtheappropriatetorque.Thetypicalstagesofmetrologyassistedflexiblejiginstallationaregivenbelow:1.settinginitialreferenceframesinthefactory2.measurementofinitialreferenceframe3.installationofbaseormainframeinitsposition4.installationofinnerframesoffline5.installationofholdingandpositioningbrackets6.installationofclamps,bushingsandpickupsintheirroughpositiononinnerframesandmainframe7.installationofinnerframeonthebaseframe8.fineadjustmentandfasteningofkeylocatingcomponents9.verificationofreferenceframesandclamps10.inservicemonitoringofkeypositionsonthejigThesestagesarerelatedtothecompleteinstallationofthejigfromthescratch.NeedlesstomentionthatincaseofslightMethodologyforHighAccuracyInstallationofSustainableJigsandFixtures153changeindesignvariationsomeofthefollowingoperationswillbeomitted.Table2:AbriefcomparisonbetweendifferentjigphilosophiesTypicalcharacteristicFixedframeFlexiblejigJig-lessApplicationLargevolumeproductionLowvolumeproductionPrototypingUniquenessRepeatableReconfigurableCosteffectivenessDurabilityVeryhighHighLowProsRigidityVeryhighUncertaintyrigidityLowWeightHeavyMediumLowPortabilityNon-portableDifficultcomponentpositioningineachsetupDifficulttoprogramCostVeryhighMediumLowConsManufacturingtimeLongMediumShort3.2AlgorithmforflexiblejiginstallationTheinstallationprocessesforflexiblejigstakethefollowingmainstages:1.theinstallationofmainframeofthejig2.theassemblyofmovingunitsandsub-systems3.theinstallationofthejiginnerframesonthejigassembly4.theassemblyofpickupsandclampsonthejig.Themainframeisthebackboneofthejigthatistypicallyfixedforalargenumberofjigtopologyanddesignvariations.Thereforeitdoesnotchangeinshapeasregularlyastheinnerframeorthesmallerelementsofthejigsuchasbushings,pickupsandclamps.Carefulconsiderationofthemanufacturingprocesscanreducethenecessityofrearranginglargerelementsofthejigcomponentsresultinginfurthertimeandmoneysaving.Figure3inthreeseparategroupsofactivitiesshowstheprocessesofflexiblejiginstallation.Inthisprocessitisassumedthatthestandardpartsofthejigareselectedfromtheavailable,offtheshelfsectionsandcomponents.Theninadvanceofthephysicalinstallationanumberoftestsandtrialsarecarriedouttoplanthejiginstallationinsuchawaythattheuncertaintyofmeasurementisreduced.Oncetheacceptablelevelofuncertaintyisachievedthephysicalinstallationcantakeplace.Figure3:MeasurementassistedinstallationprocedureforflexiblejigJ.Jamshidi,P.G.Maropoulos154Injiginstallationprocessitmightberequiredtousemultiplemeasurementsystemorameasurementsystemfromseverallocationstocoverthecompletesetofkeypointsforjiginstallation.Thisshouldincludetheauxiliarytargetreferencepointsthatareplacedonthefactoryfloorandwallforstabilityanddriftcheckduringthejigservice.Duringthelocalisationofthekeypointsonthejigtheuncertaintyofthemeasurementinstrumentshouldbetakenintoaccount.Asaruleofthumbtheaccuracyofthejigpositioningforeachkeylocationshouldbeinanorder10timesbetterthantherequiredtolerance.Inotherwordifthetoleranceonthecomponentisspecifiedas0.1mmtheaccuracyofthejigpositioningshouldbeatleast0.01mm.Thebestpracticeapproachesfortheflexiblejiginstallationaregivenbelow:1.Aplannedpositionfortheinitialreferencepointsonthefactorywallandfloorispreferredinordertominimiseuncertaintyofthemeasurement.2.Theinstrumentpositionshouldbeverifiedonregularbasesusingtheinitialreferencepoints.3.OneachlargesectionofthejigseveralSMRnestscanbeattachedforbettertrackingandrepeatability.4.Wherethelargecomponentsofthejighavebendortwistthelevelmeasurementshouldbefocussedonthecentralsectionofthebeamstoreduceangularpositioningerror.5.Thereferencepointsontheinnerframesshouldbeselectedasdistantaspossibleforcreatingframecoordinatesystems.Thiscanresultinsmalleruncertaintywhenintheinnerframecoordinatesystem.4UNCERTAINTYUncertaintyifdefinedbyGUM8astheresultoftheevaluationaimedatcharacterisingtherangewithinwhichthetrueval
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