数控英文翻译.docx

数控英文翻译.docx

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数控英文翻译

英文翻译

2013届机械制造设计及自动化专业130696班级

姓名学号130

指导教师职称教授

二О一五年三月二十七日

Chapterl

Introduction

Withtheadventofcomputers,thepromiseoffast,accurateandautomaticmachiningofpartswasborn.Pioneeringresearchintonumericallycontrolled（NC）machininginthelate1940sandearly1950s,MITsServomechanismLabsdevelopedalanguageforspecifyinggeometryandcuttingmovements,calledAPT.ThisgaveNCprogrammersaconsistentinterfacetoNCmillingmachines.

aconsistentinterfacetoNCmillingmachines.窗体顶端

窗体底端

APT´sgeometricalformattinghasbeensupplantedasCADsystemshavedevelopedtoallowmorerefinedandinteractivesurfacedefinitionandediting.Generatingcuttingtoolmovementshasalsobeensimplified,allowingsignificantincreasesinNCprogrammingproductivity.However,thebasicprocessofmachiningisstillsimilar.AdesignercreatesapartdescriptionandthenanexperiencedNCprogrammergeneratescuttingtoolpaths.Theyarethencheckedforaccuracy,oftenbycuttingmodelsoutofwoodorplastic,atime-consuminganderror-pronemethod.

窗体顶端

窗体底端

Despitethis,automatedmachininghasresultedinimprovedefficiencyandeconomicbenefit.Ultimately,however,thecompleteautomatedNCmachiningprocess,fromtheinputofapartspecificationtothefabricationandcheckingofcorrectnessofthefinalpart,wouldbeacompletelyautomaticsequenceofoperations,requiringnointervention.Thiswouldfreeuphumandesignerstodothecreativeworkwithoutworryingaboutthedetailsnecessarytoimplementit.

窗体底端

1.1Thegoalofanautomatedmachiningsystem

AcompleteautomatedNCmachiningsystemwouldbeonethattakesapartdescriptionanddoeseverythingrequiredtomanufacturethedesiredpart.Thechainofstepsneededtoaccomplishthisisnotinsignificantandeachstepisaninvolvedprocedure,callingforcomplex,interrelateddecisions.Thesystemmustbeabletomakedecisionsaboutsuchthingsasmethodsforclampingablockofmaterialwhilemachiningisgoingonaswellasdeterminingthedifferentpositiontheblockshouldbeheldandinwhatorder.Ithastoselectthecuttingtoolstouseandhowtousethemmosteffectively.

窗体顶端

窗体底端

Letustakeacloserlookatwhatisinvolvedinthemachiningprocess.[20]offersaneffectivebreakdownofthesequenceofevents:

窗体顶端

PartDesignDesignofthepartisusuallyaccomplishedwithinaCADsystemtoday.Thesesystemsarewidelyavailableandhaveinteractivecapabilitiesthatmakethemrelativelysimpletouse.

SurfaceevaluationThepartdescriptionmustbeanalyzedtolocatefeaturesthatwillsignificantlyaffectthemachiningprocess.Forexample,thisstageshoulddetectslots,bossesandlargechangesinsurfaceorientationsothattheycanbecompensatedforduringthegenerationoftheNCprogram.

MachiningPlanningTocutthepartfromapieceofstockrequiresanswerstoseveralquestions.Forexample,thesystemmustdecidehowtoclampthepartandhowmanydifferentpositionsarenecessarytoallowmachiningofthecompleteproduct.Thetypesandsizesofcuttingtoolsmustbeselected,aswellastheoverallsequenceofevents.Thisrequiresknowledgeandreasoningaboutalargenumberofdetailsconcerningtheparticularmillingmachine.

窗体顶端

窗体底端

ToolMovementGenerationOncethestrategyhasbeenplotted,theactualcutstobemademustbecalculated.ThismeansthatanNCprogrammustbecreatedthatwillcarvethedesiredsurface.Inactuality,thegoalwillbetomachineapartthatiswithinsometoleranceofthedesiredresultwheneverythingisfinished.

窗体顶端

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SimulationandVerificationTheNCprogramshouldbecheckedtoguaranteethatitproducesthedesiredsurfacetowithinacceptabletolerancelimits.Geometriccorrectnessofthecuttingprogrammustbeverified.Allowingthebodyofthemillingmachinetohitthestockoritselfduringthecuttingcouldresultinveryexpensivedamagetobothmachineandstock.Ifthefinalresultisoutoftoleranceorthereisforbiddencontactbetweensurfaces,thegeneratorcanthenreplantheNCprogram.Theloopofgenerationandsimulationmayrepeatuntileverythingissatisfactory.

窗体顶端

窗体底端

窗体底端

DynamicSimulationThepreviousstepverifiesthegeometricaccuracyoftheprogram.Thisoneanalyzestheforcesinvolved.Themorematerialremovedinagiventime,themoreforcebetweenthematerialandthetool.Theseforcescausedeflectionsinbothsurfaces,andtheresultisfurtherdeformed.However,fasterfeedrates（speedofmaterialremoval）resultinlessmachiningtime,reducingthecosts.Thesefactorsmustbebalancedandfeedratessetaccordingly.

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窗体底端

DetermineCostOncethefeedrateshavebeendetermined,calculationofcuttingtimeisstraightforward.Oncethecostsofmachininghavebeencalculated,agoaheadorstopcommandcanbeissued.

ExecuteMachiningProgramIdeally,themachiningequipmentcouldsensetheactualforcesandadjustthefeedratestokeepwithintolerance.

EvaluateFinalResultThepartthathasjustbeencutshouldbecheckedtomakesurethatitmeetstherequirementssetoutatthebeginningofthemanufacturingprocess.

Aswecansee,buildingasystemthatcandoeverythingisafairlyformidableassignment.Eachstepposeschallengesofitsown.Wewillexaminegeometricverificationinmoredetail.

1.2Verification

Thegoalofverificationisstraightforward.Givenapartdescription,anNCprogramoftoolmovements,andaworkpiecethatistobeshaped,determineiftheNCprogramshapestheworkpieceintoacopyofthepartdescription,andwhereitfailstodoso.

Thisofcourseisasimplisticstatementoftheproblem.Inmanufacturing,thequestionisreallyhowcloseisthefinalproducttothedesiredpart,asopposedtoaretheythesame.Usually,themanufacturingprocessintroducessmallerrorsintothedesiredsurface.Therefore,verificationmustactuallydetermineifthemachinedproductiswithinsomesmalltoleranceofthepart,insideorout,forallpointsonthesurface.Inaddition,verificationmustbepreparedtoidentifythelocationswheregouginghasoccurredandwheretoomuchexcessmaterialhasbeenleftbehind,ifwewishtocorrectthetoolprogram.

Anotherobjectiveofverificationistocheckthatthetooldoesn'tgougethemountinghardwareorotherpartsofthemill.Inaddition,detectionofanytoolmovementthatcausesthenon-cuttingsurfacestohitworkpiecematerialisdesirable.Otherwise,anexpensiverepairmaybeinorder.Wemayalsoliketoknowthevolumeofmaterialthatatoolmovementremovestoallowforlaterdynamicsimulations.Theselastdesiredfeaturescallforsimulationofthecuttingprocess,notjustdeterminingthefinalproductofthemilling.

Toaccomplishthesegoals,wemustrepresentthecomponentsinvolvedintheactualcuttingprocess.First,thepartdescriptionisneeded.Wemusthavearepresentationfortheworkpiecetobemachined.Thesweptvolumeofeachtoolmovementmustbeavailableinsomeusablerepresentation（somerepresentationsaremuchmoreusefulthanothersforcertainpurposes）.Andifwewishtoexamineinterferenceofsurfacesthatshouldnotcomeintocontactsuchasthemachinebody,wemusthaverepresentationsofthosesurfacesaswell.

Giventhisinformation,wemustprovideamethodforremovingthesweptvolumeofeachtoolmovementfromtheworkpiecemodel.Thetoolmovementshavetobeprocessedinorderifwewishtodosimulationoftheworkpieceandenvironmentatanytime,asopposedtojustthefinishedproduct.

Let'stakeacloserlookatthemeansdevelopedforperformingverification.

1.2.1MethodsofVerification

Thereareseveralwaysonecangoaboutperformingverification.Acommonlyavailabletechniqueistodisplaythetoolpathsontopofthepartsurface.Thishastheadvantageofbeingquitesimpletoimplement,aswellasbeingeasyonthecomputer.Thenverificationcouldbeperformedbyvisuallycomparingtoolpathsandthepartsurface.However,onlygrosserrorsarelikelytobefoundinthismanner.Itisalsotimeintensive.Sincemanufacturingoftenrequirestighttolerances,somethingbetterisneeded.Italsomakessensetohavethecomputerdoingthework,bothforthesakeofspeedandreliability.

Increasingthecomputer'sinvolvementintheverificationprocess,wecancheckforinterferencebetweenthepartsurfaceandthesweptenvelopeofeachtoolmovement.Thiswilllocatetoolmovementsthatgougethepartsurface,buthasseveraldisadvantages.Sincenomodeloftheworkpieceiskept,itisinconvenienttocomparethemachinedresulttothedesiredpartsurface.Eachtoolmovementcankeeptrackofitsimpactonthesurface,buttheoveralleffectisnotknown.Inaddition,sincethisisnotasimulation,materialremovalcannotbedetermined.

Thetwomethodsmentionedabovearenotreallysimulationsofthemachiningprocess.Toperformallofthetasksofverification,ageometricmodelofthemachiningprocessmustbemaintained.SolidModelingandDiscreteModelingarethetwomajormethodsofsimulatingmachining.

Solidmodeling

Solidmodelingwasdevelopedasawayofrepresentingcomplexsurfacesbuiltupasbooleancombinationsofsimpleobjects.Themachiningoperationisjustthisanobject（theworkpiece）fromwhichotherobjects（thetoolmovementenvelopes）aresubtracted.Anaccuratemodelofthecurrentstateoftheworkpieceismaintainedatalltimes,andmaterialremovedbyeachtoolmovementcanbedetermined.SolidmodelingsystemsforNCsimulationandverificationwereinvestigatedbyvoelckerandHuntin[34]and[17]andbyFrishdalin[12].

Usingsolidmodelingtodosimulationandverificationhasadownside,however.Simulationrequire