机械毕业设计英文外文翻译493五轴数控铣床翻译Word文档格式.docx

机械毕业设计英文外文翻译493五轴数控铣床翻译Word文档格式.docx

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E.L.J.Bohez

文献出处：

InternationalJournalofMachineTools&

Manufacture42（2002）505–520

翻译页数：

1.Introduction

Themaindesignspecificationsofamachinetoolcanbededucedfromthefollowingprinciples:

●Thekinematicsshouldprovidesufficientflexibilityin

orientationandpositionoftoolandpart.

●Orientationandpositioningwiththehighestpossible

speed.

accuracy.

●Fastchangeoftoolandworkpiece.

●Savefortheenvironment.

●Highestpossiblematerialremovalrate.

Thenumberofaxesofamachinetoolnormallyreferstothenumberofdegreesoffreedomorthenumberofindependentcontrollablemotionsonthemachineslides.TheISOaxesnomenclaturerecommendstheuseofaright-handedcoordinatesystem,withthetoolaxiscorrespondingtotheZ-axis.Athree-axismillingmachinehasthreelinearslidesX,YandZwhichcanbepositionedeverywherewithinthetravellimitofeachslide.Thetoolaxisdirectionstaysfixedduringmachining.Thislimitstheflexibilityofthetoolorientationrelativetotheworkpieceandresultsinanumberofdifferentsetups.Toincreasetheflexibilityinpossibletoolworkpieceorientations,withoutneedofre-setup,moredegreesoffreedommustbeadded.Foraconventionalthreelinearaxesmachinethiscanbeachievedbyprovidingrotationalslides.Fig.1givesanexampleofafive-axismillingmachine.

2.Kinematicchaindiagram

Toanalyzethemachineitisveryusefultomakeakinematicdiagramofthemachine.Fromthiskinematic（chain）diagramtwogroupsofaxescanimmediatelybedistinguished:

theworkpiececarryingaxesandthetoolcarryingaxes.Fig.2givesthekinematicdiagramofthefive-axismachineinFig.1.Ascanbeseentheworkpieceiscarriedbyfouraxesandthetoolonlybyoneaxis.Thefive-axismachineissimilartotwocooperatingrobots,onerobotcarryingtheworkpieceandonerobotcarryingthetool.Fivedegreesoffreedomaretheminimumrequiredtoobtainmaximumflexibilityintoolworkpieceorientation,thismeansthatthetoolandworkpiececanbeorientedrelativetoeachotherunderanyangle.Theminimumrequirednumberofaxescanalsobeunderstoodfromarigidbodykinematicspointofview.Toorienttworigidbodiesinspacerelativetoeachother6degreesoffreedomareneededforeachbody（toolandworkpiece）or12degrees.Howeveranycommontranslationandrotationwhichdoesnotchangetherelativeorientationispermittedreducingthenumberofdegreesby6.Thedistancebetweenthebodiesisprescribedbythetoolpathandallowseliminationofanadditionaldegreeoffreedom,resultinginaminimumrequirementof5degrees.

3.Literaturereview

Oneoftheearliest（1970）andstillveryusefulintroductionstofive-axismillingwasgivenbyBaughman[1]clearlystatingtheapplications.TheAPTlanguagewasthentheonlytooltoprogramfive-axiscontouringapplications.TheproblemsinpostprocessingwerealsoclearlystatedbySim[2]inthoseearlierdaysofnumericalcontrolandmostissuesarestillvalid.BoydinRef.[3]wasalsooneoftheearlyintroductions.Beziers’book[4]isalsostillaveryusefulintroduction.Held[5]givesaverybriefbutenlighteningdefinitionofmulti-axismachininginhisbookonpocketmilling.Arecentpaperapplicabletotheproblemoffive-axismachineworkspacecomputationisthemultiplesweepingusingtheDenawit-HartenbergrepresentationmethoddevelopedbyAbdel-MalekandOthman[6].Manytypesanddesignconceptsofmachinetoolswhichcanbeappliedtofive-axismachinesarediscussedinRef.[7]butnotspecificallyforthefive-axismachine.henumberofsetupsandtheoptimalorientationofthepartonthemachinetableisdiscussedinRef.[8].AreviewaboutthestateoftheartandnewrequirementsfortoolpathgenerationisgivenbyB.K.Choietal.[9].GraphicsimulationoftheinteractionofthetoolandworkpieceisalsoaveryactiveareaofresearchandagoodintroductioncanbefoundinRef.[10].

4.Classificationoffive-axismachines’kinematicstructure

StartingfromRotary（R）andTranslatory（T）axesfourmaingroupscanbedistinguished:

（i）threeTaxesandtwoRaxes;

（ii）twoTaxesandthreeRaxes;

（iii）oneTaxisandfourRaxesand（iv）fiveRaxes.Nearlyallexistingfive-axismachinetoolsareingroup（i）.Alsoanumberofweldingrobots,filamentwindingmachinesandlasermachiningcentersfallinthisgroup.Onlylimitedinstancesoffive-axismachinetoolsingroup（ii）existforthemachiningofshippropellers.Groups（iii）and（iv）areusedinthedesignofrobotsusuallywithmoredegreesoffreedomadded.Thefiveaxescanbedistributedbetweentheworkpieceortoolinseveralcombinations.Afirstclassificationcanbemadebasedonthenumberofworkpieceandtoolcarryingaxesandthesequenceofeachaxisinthekinematicchain.Anotherclassificationcanbebasedonwheretherotaryaxesarelocated,ontheworkpiecesideortoolside.ThefivedegreesoffreedominaCartesiancoordinatesbasedmachineare:

threetranslatorymovementsX,Y,Z（ingeneralrepresentedasTTT）andtworotationalmovementsAB,ACorBC（ingeneralrepresentedasRR）.Combinationsofthreerotaryaxes（RRR）andtwolinearaxes（TT）arerare.Ifanaxisisbearingtheworkpieceitisthehabitofnotingitwithanadditionalaccent.Thefive-axismachineinFig.1canbecharacterizedbyXYABZ.TheXYABaxescarrytheworkpieceandtheZ-axiscarriesthetool.Fig.3showsamachineofthetypeXYZAB_,thethreelinearaxes

carrythetoolandthetworotaryaxescarrytheworkpiece.

5.Workspaceofafive-axismachine

Beforedefiningtheworkspaceofthefive-axismachinetool,itisappropriatetodefinetheworkspaceofthetoolandtheworkspaceoftheworkpiece.Theworkspaceofthetoolisthespaceobtainedbysweepingthetoolreferencepoint（e.g.tooltip）alongthepathofthetoolcarryingaxes.Theworkspaceoftheworkpiececarryingaxesisdefinedinthesameway（thecenterofthemachinetablecanbechosenasreferencepoint）.Theseworkspacescanbedeterminedbycomputingthesweptvolume[6].Basedontheabove-definitionssomequantitativeparameterscanbedefinedwhichareusefulforcomparison,selectionanddesignofdifferenttypesofmachines.

6.Selectioncriteriaofafive-axismachine

Itisnottheobjectivetomakeacompletestudyonhowtoselectordesignafive-axismachineforacertainapplication.Onlythemaincriteriawhichcanbeusedtojustifytheselectionofafive-axismachinearediscussed.

6.1.Applicationsoffive-axismachinetools

Theapplicationscanbeclassifiedinpositioningandcontouring.Figs.12and13explainthedifferencebetweenfive-axispositioningandfive-axiscontouring.

6.1.1.Five-axispositioning

Fig.12showsapartwithalotofholesandflatplanesunderdifferentangles,tomakethispartwithathreeaxismillingmachineitisnotpossibletoprocessthepartinonesetup.Ifafive-axismachineisusedthetoolcanprocess.MoredetailsoncountouringcanbefoundinRef.[13].Applicationsoffive-axiscontouringare:

（i）productionofblades,suchascompressorandturbineblades;

（ii）injectorsoffuelpumps;

（iii）profilesoftires;

（iv）medicalprosthesissuchasartificialheartvalves;

（v）moldsmadeofcomplexsurfaces.

6.1.2.Five-axiscontouring

Fig.13showsanexampleoffive-axiscontouring,tomachinethecomplexshapeofthesurfaceweneedtocontroltheorientationofthetoolrelativetothepartduringcutting.Thetoolworkpieceorientationchangesineachstep.TheCNCcontrollerneedstocontrolallthefive-axessimultaneouslyduringthematerialremovalprocess.MoredetailsoncountouringcanbefoundinRef.[13].Applicationsoffive-axiscontouringare:

（v）

moldsmadeofcomplexsurfaces.

6.2.Axesconfigurationselection

Thesizeandweightofthepartisveryimportantasafirstcriteriontodesignorselectaconfiguration.Veryheavyworkpiecesrequireshortworkpiecekinematicchains.Alsothereisapreferenceforhorizontalmachinetableswhichmakesitmoreconvenienttofixandhandletheworkpiece.Puttingaheavyworkpieceonasinglerotaryaxiskinematicchainwillincreasetheorientationflexibilityverymuch.ItcanbeobservedfromFig.4thatprovidingasinglehorizontalrotaryaxistocarrytheworkpiecewillmakethemachinemoreflexible.Inmostcasesthetoolcarryingkinematicchainswillbekeptasshortaspossiblebecausethetoolspindledrivemustalsobecarried.

6.3.five-axesmachiningofjewelry

AtypicalworkpiececouldbeaflowershapedpartasinFig.14.Thisapplicationisclearlycontouring.Thepartwillberelativelysmallcomparedtothetoolassembly.Alsosmalldiametertoolswillrequireahighspeedspindle.Ahorizontalrotarytablewouldbeaverygoodoptionastheoperatorwillhaveagoodviewofthepart（withrange360°

）.Allaxesasworkpiececarryingaxeswouldbeagoodchoicebecausethetoolspindle

couldbefixedandmadeveryrigid.Thereare20waysinwhichtheaxescanbecombinedintheworkpiecekinematicchain（Section4.2.1）.Hereonlytwokinematicchainswillbeconsidered.CaseonewillbeaT_T_T_R_R_kinematicchainshowninFig.15.CasetwowillbeaR_R_T_T_T_kinematicchainshowninFig.16.

FormodelIamachinewitharangeofX=300mmY=250mm,Z=200mm,C=n360°

andA=360°

andamachinetoo