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TheEarlyDevelopmentOfNumericallyControlledMachineToolsThehighlysophisticatedCNCmachinetoolsoftoday,inthevastanddiverserangefoundthroughoutthefieldofmanufacturingprocessing,startedfromveryhumblebeginningsinanumberofthemajorindustrializedcountries.SomeoftheearliestresearchanddevelopmentworkinthisfieldwascompletedinUSAandamentionwillbemadeoftheUK'scontributiontothisnumericalcontroldevelopment.AmajorproblemoccurredjustaftertheSecondWorldWar,inthatprogressinallareasofmilitaryandcommercialdevelopmenthadbeensorapidthatthelevelsofautomationandaccuracyrequiredbythemodernindustrializedworldcouldnotbeattainedfromthelabourintensivemachinesinuseatthattime.Thequestionwashowtoovercomethedisadvantagesofconventionalplantandcurrentmanninglevels.Itisgenerallyackonwledgedthattheearliestworkintonumericalcontrolwasthestudycommissionedin1947bytheUSgovernment.Thestudy'sconclusionwasthatthemetalcuttingindustrythroughouttheentirecountrycouldnotcopywiththedemandsoftheAmericanAirForce,letalonetherestofindustry!Asadirectresultofthesurvey,theUSAirForcecontractedthePersonsCorporationtoseeiftheycoulddevelopaflexible,dynamic,manufacturingsystemwhichwouldmaximizeproductivity.TheMassachusettsInstituteofTechnology(MIT)wassub-contractedintothisresearchanddevelopmentbytheParsonsCorporation,duringtheperiod1949-1951,andjointlytheydevelopedthefirstcontrolsystemwhichcouldbeadaptedtoawiderangeofmachinetools.TheCincinnatiMachineToolCompanyconvertedoneoftheirstandard28inchHydro-Telmillingmachinesorathree-axisautomaticmillingmadeuseofaservo-mechanismforthedrivesystemontheaxes.Thismachinemadeuseofaservomechanismforthedrivesystemontheaxes,whichcontrolledthetablepositioning,cross-slideandspindlehead.Themachinecabbeclassifiedasthefirsttrulythreeaxiscontinuouspathmachinetoolanditwasabletogeneratearequiredshape,orcurve,bysimultaneousslidewaymotions,ifnecessary.AtaboutthesametimesastheseAmericanadvancesinmachinetoolcontrolweretakingPlace,AlfredHerbertLimitedintheUnitedKingdomhadtheirfirstMutinouspathcontrolsystemwhichbecameavailablein1956.OverthenextfewyearsinboththeUSAandEurope,furtherdevelopmentworkoccurred.Theseearlynumericalcontroldevelopmentswereprincipallyfortheaerospaceindustry,whereitwasnecessarytocutcomplexgeometricshapessuchasairframecomponentsandturbineblades.Inparallelwiththisdevelopmentofsophisticatedcontrolsystemsforaerospacerequirements,apoint-to-pointcontrollerwasdevelopedformoregeneralmachiningapplications.Theselesssophisticatedpoint-to-pointmachineswereconsiderablycheaperthantheirmorecomplexcontinuouspathcousinsandwereusedwhenonlypositionalaccuracywasnecessary.Asanexampleofpoint-to-pointmotiononamachinetoolfordrillingoperations,thetypicalmovementmightbefasttraverseoftheworkpieceunderthedrill'sposition-afterdrillingthehole,antherrapidmovetakesplacetothenexthole'sposition-afterretractionofthedrill.Ofcourse,therapidmotionoftheslidewayscouldbeachievedbyeachaxisinasequentialandindependentmanner,orsimultaneously.Ifaseparatecontrolwasutilisecforeachaxis,theformermethodoftabletravelwaslessessentialtoavoidanybacklashinthesystemtoobtaintherequireddegreeofpositionalaccuracyandsoitwasnecessarythattheapproachdirectiontothenextpointwasalwaysthesame.Theearliestexamplesofthesecheaperpoint-to-pointmachinesusuallydidnotuserecalculatingballscrews;thismeantthatthemotionswouldbesluggish,andsliderwayswouldinevitablysufferfrombacklash,butmorewillbesaidaboutthistopiclaterinthechapter.TheearlyNCmachineswere,inthemain,baseduponamodifiedmillingmachinewiththisconceptofcontrolbeingutilizedonturning,punching,grindingandawholehostofothermachinetoolslater.Towardstheendofthe1950s,hydrostaticslidewayswereoftenincorporatedformachinetoolsofhighlyprecision,whichtosonicextentovercamethesectionproblemassociatedwithconventionalslidewayresponse,whilesaveraging-outslidewayinaccuracybroughtaboutamuchincreasedpreasioninthemachinetoolandimprovedtheircontrolcharacteristicsallowsconceptofthemachiningcenterwastheproductofthisearlywork,asitallowedthemachinetomanufacturearangeofcomponentsusingawidevarietyofmachiningprocessesatasingleset-up,withouttransferofworkpiecestoothervarietymachinetools.Amachiningcenterdifferedconceptuallyinitsdesignfromthatofamillingmachine,Inthatthecuttingtoolscouldbechangedautomaticallybythetransfermachanism,orselector,fromthemagazinetospindle,orviceversa.Inthisductivelyandtheautomatictoolchangingfeatureenabledthemachiningcentertoproductivelyandefficientlymachinearangeofcomponents,byreplacingoldtoolsfornew,orreselectingthenextcutterwhilstthecurrentmachiningprocessisincycle.Inthemid1960s,aUKcompany,Molins,introducedtheiruniqueSystem24whichwasmeantrepresenttheabilityofasystemtomachinefor24hoursperday.ItcouldbethoughtofasamachiningcomplexwhichallowedaseriesofNCsinglepurposemachinetoolstobelinkedbyacomputerizedconveyorsystem.Thisconveyorallowedtheworkpiecestobepalletizedandthendirectedtoasmachinetoolasnecessary.Thiswasanearly,butadmirable,attemptataformofFlexiblemanufacturingSystemconcept,butwasunfortunatelydoomedtofailure.Itsprincipalweaknesswasthatonlyasmallproportio