外文資料--10Numerically controlled machines.pdf

12720NumericallycontrolledmachinesAutomaticlatheshavebeeninuseforalongtime,andaremostlyusedfortherapidproductionoflargenumbersofidenticalcomponents.Amorerecentdevelopmenthasbeentheuseofnumericallycontrolledmachinesfortheproductionofsmallbatchesofcomponents.Thesemachinesneednotbereseteachtimeanewcomponenthastobeproduced.AutomaticlathesSingleandmultispindleautomaticlatheshavebeenfoundtobemostusefulforthemanufactureoflargenumbersofidenticalcomponents.Thematerialusedisusuallyintheformofmetalrods,whicharefedinthroughthehollowspindlesofthelathes.Mechanicaldeviceslikecamsandstopsareusedtocarryoutaseriesofoperationsaccordingto2ipredeterminedprogram.Thesetting-uptimeisusuallylong,andsuchlathesareusuallyunsuitableforsmallbatchproduction.ComputerNumericalControlMostcomponentsrequiredbyindustryneedtobeproducedonlyinsmallandmediumsizedbatches,andtheirproductiondoesnotjustifytheuseofautomaticlathes.Inthepast,theproductionofsmallandmediumsizedbatcheswasachievedbytheuseofconventionalmachinetoolsandhighlyskilledlabour.Thisresultedinalowmachineutilizationtime,alongwaitingtime,andahighcostofproduction.Theaccurateproductionofcomponentsaccordingtoadefinitetimeschedulewasextremelydifficult.Asolutiontothisproblemwasfoundbythedevelopmentofasystemofautomaticproduction.Inthissystem,themachineproducesacomponentautomaticallyinaccordancewithpredeterminedinstructions,whichcanbeeasilychangedwhenanothercomponentistobemanufactured.Theuseofaprogrammedcomputerinmachinetoolshasledtothistypeofautomationbeingcalledcomputernumericalcontrol(CNC),Incomputernumericalcontrol,theoperationofamachinetooliscontrolledbyaprogramrunonacomputer.Themachinetoolsusedinthistypeofworkhavemovementsanddriveswhicharedifferentfromthoseinconventionalmachinetools.Theyhaveelectricaldriveswhicharecontrolledbyacomputer.The12820Numericallycontrolledmachinesmachinesdonotneedtobesetupbyaskilledoperator,eachtimeanewtypeofcomponentismade.Theyworkautomaticallyundercomputercontrol,andonlyachangeinthecomputerprogramisrequiredtoproduceanewbatchofcomponents.Suchasystemhasthefollowingadvantages:1.Theflexibilityofthesystemresultsinhighmachineutilizationtimes.2.Deliveriescanbemadeontimebecauseproductionismorepredictable.3.Specialtooling(e.gusingjigsorfixtures)isnotrequired.4.Consistencyinthequalityofthegoodsproducedreducesinspectiontimes.5.Non-machiningtimeisreducedduetoautomatictoolchanging,automaticclamping,etc.6.Designchangescanbeeasilymade,becauseonlytheprogramhastobechangedtoproduceanewcomponent.7.Theskilloftheoperatorisunimportant,becausetheaccuracyisonlydependentonthemachineandtheprogram.8.Estimationofcostsiseasierthaninpreviousmethodsofproduction.MachiningandturningcentresTwomajortypesofCNCmachinetoolsaremachiningcentresandturningcentres,Amachiningcentreisamachinewhichcanperformmilling,drilling,boring,reaming,andtappingoperations,andissimilartoamillingmachine.Turningcentresarebasicallysimilartolathes.Inadditiontotheusual,shaft,bar,andchuckwork,operationslikecontourmilling,tapping,makingT-slotsandkeyways,etc.canbedonebyturningcentres.Thesemachineshavemanyfeatureswhichensureaccurateperformanceandproductivityoverlongperiodsoftime.Someofthefeaturesarethefollowing:1.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/beweglichadjhollowidenticalimportantindicationinstructionmachiningcentrenumericalcontrolpredeterminepredictablepreviousrecirculatingselectsetting-upslidingstabilityturningcentreutilizationhohladjidentischadjwichtigadjAnzeige/BefehlmBearbeitungszentrumnNumerischeSteuerung/vorherbestimmenvvoraussagbaradjvorheradjumlaufendadjauswahlenvEinstellung/gleitendadjStabilitat/CNCDrehmaschine/Nutzung/13020NumericallycontrolledmachinesExercisesXX1.Answerthefollowingquestions:a)Whatareautomaticlathesusedfor?b)Howweresmallbatchesofcomponentsproducedinthepast?c)Whatwerethedisadvantagesofthepreviousmethodsofproduction?d)HowisnonmachiningtimereducedinaCNCmachine?e)InwhatwaydothedrivesinCNCmachinesdifferfromthoseinconventionalmachines?f)WhydoestheuseofCNCresultinhighmachineutilizationtimes?g)Whatarethechangesthathavetobemade,whenanewcomponenthastobeproducedusingaCNCmachine?h)WhyistheskilloftheoperatorunimportantinaCNCmachine?i)HowaretoolschangedinaCNCmachine?j)HowisthewearonaCNCmachineminimized?2.Fillinthegapsinthefollowingsentences:a)Automaticlathesarefortheofa