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1、P113NumericalcontrolNumericalcontrolofmachinetoolsmaybedefinedasamethodofautomationinwhichvariousfunctionsofmachinetoolsarecontrolledbyletters,numbersandsymbols.BasicallyaNCmachinerunsonaprogramfedtoit.Theprogramconsistsofpreciseinstructionsaboutthemanufacturingmethodolog
2、yaswellasthemovements.Forexample,whattoolistobeused,atwhatspeed,atwhatfeedandtomovefromwhichpointtowhichpointinwhatpath,alltheseinstructionsaregiven.Sincetheprogramisthecontrollingpointforproductmanufacture,themachinebecomesversatileandcanbeusedforanypart.Allthefunctionso
3、fanNCmachinetoolarethereforecontrolledelectronically,hydraulicallyorpneumatically.InNCmachinetoolsoneormoreofthefollowingfunctionsmaybeautomatic:(1)Startingandstoppingofthemachinetoolspindle.(1)Controllingthespindlespeed.(2)Positioningthetooltipatdesiredlocationsandguidin
4、gitalong.Desiredpathsbyautomaticcontrolofthemotionofslides.(3)Controllingtherateofmovementofthetooltip.(4)Changingoftoolsinthespindle.InitiallytheneedofNCmachinewasfeltformachiningcomplexshapedsmallbatchcomponentsasthosebelongingtoanaircraft.However,thisspectrumcurrentlye
5、ncompassespracticallyallactivitiesofmanufacturing,inparticularcapitalgoodsandwhitegoods.Thustherangecoveredisverywide.Besidesmachiningwithwhichweareconcernedinthisbook,NChasbeenusedinavarietyofmanufacturingsituations.ThemajorityofapplicationsofNCareinmetalcuttingmachineto
6、olssuchasmillingmachines,lathes,drillingmachines,grindingmachinesandgeargeneratingmachines.Besideanumberofmetalformingmachinetoolssuchaspresses,flamecuttingmachines,pipebendingandformingmachines,foldingandshearingmachinesalsouseNCfortheirprogramcontrol.Theinspectionmachin
7、escalledCo-ordinateMeasuringMachinesarealsobasedonNC.Lastlytherobotsbasicallymaybematerialhandlingunits,buttheircontrolprinciplesareveryclosetotheNC.Besidestheseapplicationslistedformanufacturing,otherapplicationssuchasfilamentwindingorassemblymachinesbasedontheNCprincipl
8、escanalsobeseenintheindustry.NCmachineshavebeenfoundsuitableforthefollowing:(1)Partshavingcomple
