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外文资料--10Numerically controlled machines.pdf

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外文资料--10Numerically controlled machines.pdf

12720NumericallycontrolledmachinesAutomaticlatheshavebeeninuseforalongtime,andaremostlyusedfortherapidproductionoflargenumbersofidenticalcomponents.Amorerecentdevelopmenthasbeentheuseofnumericallycontrolledmachinesfortheproductionofsmallbatchesofcomponents.Thesemachinesneednotbereseteachtimeanewcomponenthastobeproduced.AutomaticlathesSingleandmultispindleautomaticlatheshavebeenfoundtobemostusefulforthemanufactureoflargenumbersofidenticalcomponents.Thematerialusedisusuallyintheformofmetalrods,whicharefedinthroughthehollowspindlesofthelathes.Mechanicaldeviceslikecamsandstopsareusedtocarryoutaseriesofoperationsaccordingto2ipredeterminedprogram.Thesettinguptimeisusuallylong,andsuchlathesareusuallyunsuitableforsmallbatchproduction.ComputerNumericalControlMostcomponentsrequiredbyindustryneedtobeproducedonlyinsmallandmediumsizedbatches,andtheirproductiondoesnotjustifytheuseofautomaticlathes.Inthepast,theproductionofsmallandmediumsizedbatcheswasachievedbytheuseofconventionalmachinetoolsandhighlyskilledlabour.Thisresultedinalowmachineutilizationtime,alongwaitingtime,andahighcostofproduction.Theaccurateproductionofcomponentsaccordingtoadefinitetimeschedulewasextremelydifficult.Asolutiontothisproblemwasfoundbythedevelopmentofasystemofautomaticproduction.Inthissystem,themachineproducesacomponentautomaticallyinaccordancewithpredeterminedinstructions,whichcanbeeasilychangedwhenanothercomponentistobemanufactured.TheuseofaprogrammedcomputerinmachinetoolshasledtothistypeofautomationbeingcalledcomputernumericalcontrolCNC,Incomputernumericalcontrol,theoperationofamachinetooliscontrolledbyaprogramrunonacomputer.Themachinetoolsusedinthistypeofworkhavemovementsanddriveswhicharedifferentfromthoseinconventionalmachinetools.Theyhaveelectricaldriveswhicharecontrolledbyacomputer.The12820Numericallycontrolledmachinesmachinesdonotneedtobesetupbyaskilledoperator,eachtimeanewtypeofcomponentismade.Theyworkautomaticallyundercomputercontrol,andonlyachangeinthecomputerprogramisrequiredtoproduceanewbatchofcomponents.Suchasystemhasthefollowingadvantages1.Theflexibilityofthesystemresultsinhighmachineutilizationtimes.2.Deliveriescanbemadeontimebecauseproductionismorepredictable.3.Specialtoolinge.gusingjigsorfixturesisnotrequired.4.Consistencyinthequalityofthegoodsproducedreducesinspectiontimes.5.Nonmachiningtimeisreducedduetoautomatictoolchanging,automaticclamping,etc.6.Designchangescanbeeasilymade,becauseonlytheprogramhastobechangedtoproduceanewcomponent.7.Theskilloftheoperatorisunimportant,becausetheaccuracyisonlydependentonthemachineandtheprogram.8.Estimationofcostsiseasierthaninpreviousmethodsofproduction.MachiningandturningcentresTwomajortypesofCNCmachinetoolsaremachiningcentresandturningcentres,Amachiningcentreisamachinewhichcanperformmilling,drilling,boring,reaming,andtappingoperations,andissimilartoamillingmachine.Turningcentresarebasicallysimilartolathes.Inadditiontotheusual,shaft,bar,andchuckwork,operationslikecontourmilling,tapping,makingTslotsandkeyways,etc.canbedonebyturningcentres.Thesemachineshavemanyfeatureswhichensureaccurateperformanceandproductivityoverlongperiodsoftime.Someofthefeaturesarethefollowing1.Themachinesareofmassiveconstruction.Thisgivesthemthestabilityneededtowithstandlargecuttingforces,andthethermaleffectscausedbythelargequantitiesofchipsproduced.2.Minimizationofwearisachievedbytheuseofrollingcomponentsinsteadofslidingcomponents.20Numericallycontrolledmachines1293.Thescrewthreadsofconventionalmachinesarereplacedbycirculatingballscrews.Rigidmountingtechniquesforbearingsandscrewsandalsopreloadingaretechniquesusedforovercomingbacklash.4.Eachtoolisheldinanadaptor,andstoredinadrum,chain,orothertypeofmagazine.Thecorrecttoolforanoperationisselectedautomaticallyfromamagazine,andisusedtoreplacetheonealreadyexistingonthemachine.5.Measuringinstrumentsgiveacontinuousindicationofthepositionofthecuttingtool.Thesearecomparedwiththedesiredvaluesbythecomputerandcorrectedwhennecessary.Theuseofsuchatechniqueautomaticallycompensatesfortoolwear.VocabularyaccordanceachieveadaptorautomaticbacklashbatchcompensateconstructioncontinuousconventionaldevelopmentdifficultdrumestimationexistextremelyfeatureflexibleUbereinstimmung/leistenvAufnehmermautomatischadjFlankenspielnMenge,LosgroBe/kompensierenvAniage/standigadjherkommlichadjEntwicklung/schweradjTrommel/Schatzung/existierenvsehradvEigenschaft/beweglichadjhollowidenticalimportantindicationinstructionmachiningcentrenumericalcontrolpredeterminepredictablepreviousrecirculatingselectsettingupslidingstabilityturningcentreutilizationhohladjidentischadjwichtigadjAnzeige/BefehlmBearbeitungszentrumnNumerischeSteuerung/vorherbestimmenvvoraussagbaradjvorheradjumlaufendadjauswahlenvEinstellung/gleitendadjStabilitat/CNCDrehmaschine/Nutzung/13020NumericallycontrolledmachinesExercisesXX1.AnswerthefollowingquestionsaWhatareautomaticlathesusedforbHowweresmallbatchesofcomponentsproducedinthepastcWhatwerethedisadvantagesofthepreviousmethodsofproductiondHowisnonmachiningtimereducedinaCNCmachineeInwhatwaydothedrivesinCNCmachinesdifferfromthoseinconventionalmachinesfWhydoestheuseofCNCresultinhighmachineutilizationtimesgWhatarethechangesthathavetobemade,whenanewcomponenthastobeproducedusingaCNCmachinehWhyistheskilloftheoperatorunimportantinaCNCmachineiHowaretoolschangedinaCNCmachinejHowisthewearonaCNCmachineminimized2.FillinthegapsinthefollowingsentencesaAutomaticlathesarefortheofalargenumberofcomponents.bAnewhasbeentheuseofcontrolledmachinesforproduction.cPreviously,smallbatchproductionwasusinglabourandmachinetools.dThisresultedinalowmachinetimeandahighofproduction.eTheofaCNCmachineisbyacomputerprogram.fSpecialtoolslikejigsandarenotwhenaCNCmachineisused.

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