电子教案统一模板(数控)Unit4

Unit4TheComponentsofCNCMachinesLesson7TheConstructionofCNCMachines4.1Lesson8TheComponentsofCNCMachines4.2ReadingMaterials7TheOperationPanelofCNCMachinesⅠ4.3ReadingMaterials8TheOperationPanelofCNCMachinesⅡ4.44.1Lesson7TheConstructionofCNCMachinesCNCmachinetoolsarecomplexassemblies.Ingeneral,CNCmachinetoolconsistsofthefollowingunits:1.Computer—Aswithallcomputers,theCNCmachinecomputerworksonabinaryprincipleusingonlytwocharacters1and0,forinformationprocessingprecisetimeimpulsesfromthecircuit.Therearetwostates,astatewithvoltage,1,andastatewithoutvoltage,0.Seriesofonesandzeroesaretheonlystatesthatthecomputerdistinguishesacalledmachinelanguage,whichistheonlylanguagethecomputerunderstands.Whencreatingtheprogram,theprogrammerdoesnotcareaboutthemachinelanguage.Heorshesimplyusesalistofcodesandkeysinthemeaningfulinformation.Specialbuilt-insoftwarecompilestheprogramintomachinelanguageandthemachinemovesthetoolbyitsservomotors.However,theprogrammabilityofthemachineisdependentonwhetherthereisacomputerinthemachine’scontrol.2.Controlsystem—TherearetwotypesofcontrolsystemsonNC/CNCmachines:open-loopandclosed-loop.Thetypeofcontrolloopuseddeterminestheoverallaccuracyofthemachine.Theopen-loopcontrolsystemdoesnotprovidepositioningfeedbacktothecontrolunit.Theclosed-loopcontrolsystemisveryaccurate.Ithasanautomaticcompensativefunctionforerror,sincethefeedbackdeviceindicatestheerrorandthecontrolmakesthenecessaryadjustmentstobringtheslidebacktotheposition.TheyapplyAC,DCorhydraulicservomotors.3.Drivemotors—ThedrivemotorscontrolthemachineslidemovementonNC/CNCequipment.Theyfallintofourbasictypes:Steppermotorsconvertadigitalpulsegeneratedbythemicrocomputerunit(MCU)intoasmallsteprotation.Steppermotorsareusedinopen-loopcontrolsystems,whileAC,DCorhydraulicservomotorsareusedinclosed-loopcontrolsystems.Directcurrent(DC)servomotorsarevariablespeedmotorsthatrotateinresponsetotheappliedvoltage.Theyareusedtodrivealeadscrewandgearmechanism.DCservomotorsprovidehigher-torqueoutputthansteppermotors.Alternativecurrent(AC)servomotorsarecontrolledbyvaryingthevoltagefrequencytocontrolspeed.TheycandevelopmorepowerthanaDCservomotor.Theyarealsousedtodrivealeadscrewandgearmechanism.Fluidorhydraulicservomotorsarealsovariablespeedmotors.Theyareabletoproducemorepower,ormorespeedinthecaseofpneumaticmotorsthanelectricservomotors.ThehydraulicpumpprovidesenergytovalvesthatarecontrolledbytheMCU.4.Toolchangers—Inacommonmachining,severaldifferentcuttingtoolsareusedtoproduceapart.Thetoolsmustbereplacedquicklyforthenextmachiningoperation.Forthisreason,themajorityofNC/CNCmachinetoolsareequippedwithautomatictoolchangers,suchasmagazinesonmachiningcentersandturretsonturningcenters.Theyallowtoolchangingwithouttheinterventionoftheoperator.4.2Lesson8TheComponentsofCNCMachinesThemaincomponentsofCNCmachiningcentersarethebed,saddle,column,table,servomotors,ballscrews,spindle,toolchanger,andthemachinecontrolunit(Figure4-1).Bed—Thebedisusuallymadeofhigh-qualitycastironwhichprovidesforarigidmachinecapabilityofperformingheavy-dutymachiningandmaintaininghighprecision.Hardenedandgroundwaysaremountedtothebedtoproviderigidsupportforalllinearaxes.Saddle—Thesaddle,whichismountedonthehardenedandgroundbed-ways,providesthemachiningcenterwiththeXaxislinearmovement.Column—Thecolumn,whichismountedtothesaddle,isdesignedwithhightorsionstrengthtopreventdistortionanddeflectionduringmachining.ThecolumnprovidesthemachiningcenterwiththeYaxislinearmovement.Table—Thetable,whichismountedonthebed,providesthemachiningcenterwiththeZaxislinearmovement.Servosystem—Theservosystem,whichconsistsofservodrivemotors,ballscrew,andpositionfeedbackencoders,providesfast,accuratemovementandpositioningoftheXYZaxisesslides.Thefeedbackencodersmountedontheendsoftheballscrewsformaclosed-loopsystemwhichmaintainsconsistenthigh-positioningunidirectionalrepeatabilityof＋0.003mm.Spindle—Thespindle,whichisprogrammablein1r/minincrements,hasaspeedrangeoffrom20to6000r/min.Toolchangers—Therearebasicallytwotypesoftoolchangers,theverticaltoolchangerandthehorizontaltoolchanger.Thetoolchangeriscapableofstoringanumberofpresstoolswhichcanbeautomaticallycalledforusebythepartprogram.Toolchangersareusuallybidirectional,whichallowsfortheshortesttraveldistancetorandomlyaccessatool[1].MCU—TheMCUallowstheoperatortoperformavarietyofoperationssuchasprogramming,machining,diagnosis.NewerMCUsarebecomingmoresophisticated,makingmachinetoolsmorereliableandtheentiremachiningoperationslessdependentonhumanskills.FortheCNClathe(Figure4-2),thecomponentsareasfollow：Bed—ThebedofaCNClatheisofasupportfunction,forexample,thetailstock,andusuallyslantedtoallowchipstofallawayeasily.Headstock—Theheadstockcontainsthespindleandtransmissiongearingusedtorotatethespindle.Chuck—Thechuckconnectstothespindleandclampsthework-piece.Turret—Theturretholdsthecuttingtoolandreplacesanoldtoolwithanewtoolduringatoolchange.Carriage—Thecarriagemovesthecuttingtoolintotherevolvingwork-piece.Itcontainsthesaddle,cross-slide,andapron.Tailstock—Thetailstocksupportstherightendofth