数字控制计算机数字控制与计算机数控机床的安全和维护Word文件下载.docx

数字控制计算机数字控制与计算机数控机床的安全和维护Word文件下载.docx

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NC、CNCandMaintenanceforCNCMachine

1.1TheHistoryofNCandCNCDevelopment

NumericalControl（NC）isanymachiningprocessinwhichtheoperationsareexecutedautomaticallyinsequencesasspecifiedbytheprogramthatcontainstheinformationforthetoolmovements.TheNCconceptwasproposedinthelate1940sbyJohnParsonsofTraverseCity,Michigan.Parsonsrecommendedamethodofautomaticcontrolthatwouldguideamillingcuttertoproducea”thru-axiscurve”inordertogeneratesmoothprofilesonworkpieces.

In1949，TheU.S.AirForceawardParsonsacontracttodevelopanewtypeofmachinetoolthatwouldbeabletospeedupproductionmethods.ParsonscommissionedtheMassachusettsInstituteofTechnology（M.I.T）TOdevelopapracticalimplementationofhisconcept.ScientistsandengineersatM.I.Tbuiltacontrolsystemforatwo-axismillingmachinethatusedaperforatedpapertapeastheinputmedia.Inashortperiodoftime,allmajormachinetoolmanufacturerswereproducingsomemachineswithNC,butitwasnotuntilthelate1970sthatcomputer-basedNCbecamewidelyused.NCmaturedasanautomationtechnologywheninexpensiveandpowerfulmicroprocessorsreplacedhard-wirelogic-makingcomputer-basedNCsystems.

WhenNumericalControlisperformedundercomputersupervision,itiscalledComputerNumericalControl（CNC）.ComputersarethecontrolunitsofCNCmachines,theyarebuiltinorlinkedtothemachinesviacommunicationschannels.Whenaprogrammerinputsomeinformationintheprogrambytapeandsoon,thecomputercalculatesallnecessarydatatogetthejobdone.

OnthefirstNumericallyControlled（NC）machineswerecontrolledbytape,andbecauseofthat,theNCsystemswereknownastape-controlledmachines.Theywereabletocontrolasingleoperationenteredintothemachinebypunchedonmagnetictape.Therewasnopossibilityofeditingtheprogramonthemachine.Tochangetheprogram,newtapehadtobemade.

Today’ssystemshavecomputerstocontroldata;

theyarecalledComputerNumericallyControlled（CNC）machines.ForbothNCandCNCsystems,workingprinciplesarethesame.Onlythewayinwhichtheexecutioniscontrolledisdifferent.Normally,newsystemsarefaster,morepowerful,andmoreversatile.

1.2TheApplicationsofNC/CNC

Fig1-1Amoderncenterwithaten-stationturretthatacceptsquick-changetools

Sinceitsintroduction,NCtechnologyhasfoundmanyapplications,includinglathsandturningcenters,millingmachinesandmachiningcenters,punches,electricaldischargemachines（EDM）,flamecutters,grinders,andinspectionequipment.ThemostcomplexCNCmachinetoolsaretheturningcenter,showninFig.1-1（Amodemturningcenterwithaten-stationturretthatacceptsquick-changetools.EachtoolcanbepositionedinSecondswiththepressofabutton）.AndthemachiningcentershowninFig.1-2（Verticalmachiningcenter,thetoolmagazineisontheleftofthemachine.Thecontrolpanelontherightcanbeswiveledbytheoperator）andFig.1-3（Horizontalmachiningcenter,equippedwithanautomatictoolchanger.Toolmagazinescanstore200cuttingtools）.

Fig.1-2Avertical–spindlemachiningcenter

Fig.1-3Ahorizontal-spindlemachiningcenter

Whenpreparingaprogramforaparticularoperation,theprogrammermustselectallcuttingdatausingrecommendationsforconventionalmachining.Thisincludesproperselectionofcuttingspeeds,federate,toolsandtoolgeometry,andsoon.Whentheprogrammerhaschosenallofthenecessaryinformationproperly,Theoperatorloadstheprogramintothemachineandpressesabuttontostartthecuttingcycle.TheCNCmachinemovesautomaticallyfromonemachiningoperationtoanother,changingthecuttingtoolsandapplyingthecoolant.Inasurprisinglyshorttime,theworkpieceismachinedaccordingtothehighestqualitystandards.Butthatisnotall.Nomatterhowbigtheworkseriesis,allofthepartswillbealmostidenticalinsizeandsurfacefinishing.Atthistimeofadvancedtechnology,withitshighdemandsforsurfacefinishingandtolerancesofcomponentsin,forexample,aerospace,nuclear,andmedicalequipmentmanufacturing,onlyCNCmachinesprovidesuccessfulresults.

1.3TheAdvantagesandDisadvantagesofCNCMachines

1.CNCmachineshavemanyadvantagesoverconventionalmachines,someofthemare:

（1）Thereisapossibilityofperformingmultipleoperationsonthesamemachineinonesetup.

（2）becauseofthepossibilityofsimultaneousmulti-axistoolmovementspecialprofiletoolsarenotnecessarytocutunusualpartshapes.

（3）ThescraprateissignificantlyreducedbecauseoftheprecisionoftheCNCmachineandlesseroperatorimpact.

（4）ItiseasytoincorporatepartdesignchangeswhenCAD/CAMsystemsareused.

（5）Itiseasiertoperformqualityassurancebyaspot-checkinsteadof