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
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APT´sgeometricalformattinghasbeensupplantedasCADsystemshavedevelopedtoallowmorerefinedandinteractivesurfacedefinitionandediting.Generatingcuttingtoolmovementshasalsobeensimplified,allowingsignificantincreasesinNCprogrammingproductivity.However,thebasicprocessofmachiningisstillsimilar.AdesignercreatesapartdescriptionandthenanexperiencedNCprogrammergeneratescuttingtoolpaths.Theyarethencheckedforaccuracy,oftenbycuttingmodelsoutofwoodorplastic,atime-consuminganderror-pronemethod.
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Despitethis,automatedmachininghasresultedinimprovedefficiencyandeconomicbenefit.Ultimately,however,thecompleteautomatedNCmachiningprocess,fromtheinputofapartspecificationtothefabricationandcheckingofcorrectnessofthefinalpart,wouldbeacompletelyautomaticsequenceofoperations,requiringnointervention.Thiswouldfreeuphumandesignerstodothecreativeworkwithoutworryingaboutthedetailsnecessarytoimplementit.
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1.1Thegoalofanautomatedmachiningsystem
AcompleteautomatedNCmachiningsystemwouldbeonethattakesapartdescriptionanddoeseverythingrequiredtomanufacturethedesiredpart.Thechainofstepsneededtoaccomplishthisisnotinsignificantandeachstepisaninvolvedprocedure,callingforcomplex,interrelateddecisions.Thesystemmustbeabletomakedecisionsaboutsuchthingsasmethodsforclampingablockofmaterialwhilemachiningisgoingonaswellasdeterminingthedifferentpositiontheblockshouldbeheldandinwhatorder.Ithastoselectthecuttingtoolstouseandhowtousethemmosteffectively.
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Letustakeacloserlookatwhatisinvolvedinthemachiningprocess.[20]offersaneffectivebreakdownofthesequenceofevents:
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PartDesignDesignofthepartisusuallyaccomplishedwithinaCADsystemtoday.Thesesystemsarewidelyavailableandhaveinteractivecapabilitiesthatmakethemrelativelysimpletouse.
SurfaceevaluationThepartdescriptionmustbeanalyzedtolocatefeaturesthatwillsignificantlyaffectthemachiningprocess.Forexample,thisstageshoulddetectslots,bossesandlargechangesinsurfaceorientationsothattheycanbecompensatedforduringthegenerationoftheNCprogram.
MachiningPlanningTocutthepartfromapieceofstockrequiresanswerstoseveralquestions.Forexample,thesystemmustdecidehowtoclampthepartandhowmanydifferentpositionsarenecessarytoallowmachiningofthecompleteproduct.Thetypesandsizesofcuttingtoolsmustbeselected,aswellastheoverallsequenceofevents.Thisrequiresknowledgeandreasoningaboutalargenumberofdetailsconcerningtheparticularmillingmachine.
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ToolMovementGenerationOncethestrategyhasbeenplotted,theactualcutstobemademustbecalculated.ThismeansthatanNCprogrammustbecreatedthatwillcarvethedesiredsurface.Inactuality,thegoalwillbetomachineapartthatiswithinsometoleranceofthedesiredresultwheneverythingisfinished.
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SimulationandVerificationTheNCprogramshouldbecheckedtoguaranteethatitproducesthedesiredsurfacetowithinacceptabletolerancelimits.Geometriccorrectnessofthecuttingprogrammustbeverified.Allowingthebodyofthemillingmachinetohitthestockoritselfduringthecuttingcouldresultinveryexpensivedamagetobothmachineandstock.Ifthefinalresultisoutoftoleranceorthereisforbiddencontactbetweensurfaces,thegeneratorcanthenreplantheNCprogram.Theloopofgenerationandsimulationmayrepeatuntileverythingissatisfactory.
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DynamicSimulationThepreviousstepverifiesthegeometricaccuracyoftheprogram.Thisoneanalyzestheforcesinvolved.Themorematerialremovedinagiventime,themoreforcebetweenthematerialandthetool.Theseforcescausedeflectionsinbothsurfaces,andtheresultisfurtherdeformed.However,fasterfeedrates(speedofmaterialremoval)resultinlessmachiningtime,reducingthecosts.Thesefactorsmustbebalancedandfeedratessetaccordingly.
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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