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NC-3e-SI11-14,14/06,06/04/07,09/09/0723Chapter7NUMERICALCONTROLREVIEWQUESTIONS7.1Whatisnumericalcontrol?Answer:Asdefinedinthetext,numericalcontrol(NC)isaformofprogrammableautomationinwhichthemechanicalactionsofamachinetoolorotherequipmentarecontrolledbyaprogramcontainingcodedalphanumericdata.7.2WhatarethethreebasiccomponentsofanNCsystem?Answer:Thethreecomponentsare(1)thepartprogramofinstructions,(2)themachinecontrolunit,and(3)theprocessingequipment(e.g.,machinetool)thataccomplishestheoperation.7.3Whatistheright-handruleinNCandwhereisitused?Answer:Theright-handruleisusedtodistinguishpositiveandnegativedirectionsfortherotationalaxesinNC.Usingtherighthandwiththethumbpointinginthepositivelinearaxisdirection(x,y,orz),thefingersofthehandarecurledinthepositiverotationaldirectionforthea,b,andcaxes.7.4Whatisthedifferencebetweenpoint-to-pointandcontinuouspathcontrolinamotioncontrolsystem?Answer:Point-to-pointsystemsmovetheworktabletoaprogrammedlocationwithoutregardforthepathtakentogettothatlocation.Bycontrast,continuouspathsystemsarecapableofcontinuoussimultaneouscontroloftwoormoreaxes,thusprovidingcontrolofthetooltrajectoryrelativetotheworkpart.7.5Whatislinearinterpolation,andwhyisitimportantinNC?Answer:Linearinterpolationisthecapabilitytomachinealongastraight-linetrajectorythatmaynotbeparalleltooneoftheworktableaxes.ItisimportantinNCbecausemanyworkpiecegeometriesrequirecutstobemadealongstraightlinestoformstraightedgesandflatsurfaces,andtheanglesofthelinesarenotbeparalleltooneoftheaxesinthecoordinatesystem.7.6Whatisthedifferencebetweenabsolutepositioningandincrementalpositioning?Answer:Inabsolutepositioning,theworkheadlocationsarealwaysdefinedwithrespecttotheoriginoftheNCaxissystem.Inincrementalpositioning,thenextworkheadpositionisdefinedrelativetothepresentlocation.7.7Howiscomputernumericalcontrol(CNC)distinguishedfromconventionalNC?Answer:CNCisanNCsystemwhosemachinecontrolunitisadedicatedmicrocomputerratherthanahard-wiredcontroller,asinconventionalNC.7.8NamefiveofthetenfeaturesandcapabilitiesofamodernCNCmachinecontrolunitlistedinthetext.Answer:Thetenfeaturesandcapabilitiesidentifiedinthetextare(1)storageofmorethanonepartprogram,(2)variousformsofprograminput,suchaspunchedtape,magnetictape,floppydiskette,RS-232communicationswithexternalcomputers,andmanualdatainput,(3)programeditingatthemachinetool,(4)fixedcyclesandprogrammingsubroutines(macros),(5)linearandcircularinterpolation,(6)workpiecepositioningfeaturesforsetup,(7)cutterlengthandsizecompensation,(8)accelerationanddecelerationcalculationswhenthecutterpathchangesabruptly,(9)communicationsinterface,and(10)diagnosticstodetectmalfunctionsanddiagnosesystembreakdowns.7.9Whatisdistributednumericalcontrol(DNC)?Answer:DistributednumericalcontrolisadistributedcomputersysteminwhichacentralcomputercommunicateswithmultipleCNCmachinecontrolunits.Itevolvedfromdirectnumericalcontrolinwhichthecentralcomputerplayedtheroleofthetapereader,downloadingpartprogramsoneblockatatime.InamoderndistributedNCsystem,entirepartprogramsaredownloadedtotheMCUs.Alsoshopfloordataiscollectedbythecentralcomputertomeasureshopperformance.7.10Whataresomeofthemachinetooltypestowhichnumericalcontrolhasbeenapplied?NC-3e-SI11-14,14/06,06/04/07,09/09/0724Answer:NChasbeenappliedtonearlyallmachinetoolstypes,includinglathes,boringmills,drillpresses,millingmachines,andcylindricalgrinders.7.11Whatisamachiningcenter?Answer:Asdefinedinthetext,amachiningcenterisamachinetoolcapableofperformingmultiplemachiningoperationsonasingleworkpieceinonesetup.Theoperationsinvolverotatingcutters,suchasmillinganddrilling,andthefeaturethatenablesmorethanoneoperationtobeperformedinonesetupisautomatictool-changing.7.12Namefourofthesixpartcharacteristicsthataremostsuitedtotheapplicationofnumericalcontrollistedinthetext.Answer:Thesixpartcharacteristicsidentifiedinthetextarethefollowing:(1)batchproduction,(2)repeatorders,(3)complexpartgeometry,(4)muchmetalneedstoberemoved,(5)manyseparatemachiningoperationsonthepart,and(6)thepartisexpensive.7.13AlthoughNCtechnologyismostcloselyassociatedwithmachinetoolapplications,ithasbeenappliedtootherprocessesalso.Namethreeofthesixexampleslistedinthetext.Answer:Thesixnon-machinetoolapplicationslistedinthetextare(1)electricalwire-wrapmachines,(2)componentinsertionmachines,(3)draftingmachines(x-yplotters),(4)coordinatemeasuringmachines,(5)tapelayingmachinesforpolymercomposites,and(6)filamentwindingmachinesforpolymercomposites.7.14Whatarefouradvantagesofnumericalcontrolwhenproperlyappliedinmachinetooloperations?Answer:Thetextliststhefollowing11advantages:(1)nonproductivetimeisreduced,(2)greateraccuracyandrepeatability,(3)lowerscraprates,(4)inspectionrequirementsarereduced,(5)more-complexpartgeometriesarepossible,(6)engineeringchangescanbeaccommodatedmoregracefully,(7)simplerfixturesareneeded,(8)shortermanufacturingleadtimes,(9)reducedpartsinventory,(10)lessfloorspacerequiredduetofewermachines,and(11)operatorskillrequirementsarereduced.7.15WhatarethreedisadvantagesofimplementingNCtechnology?Answer:Fou