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徐州工程学院毕业设计论文1翻译部分英文部分ADVANCEDMACHININGPROCESSESAsthehardwareofanadvancedtechnologybecomesmorecomplex,newandvisionaryapproachestotheprocessingofmaterialsintousefulproductscomeintocommonuse.Thishasbeenthetrendinmachiningprocessesinrecentyears..Advancedmethodsofmachinecontrolaswellascompletelydifferentmethodsofshapingmaterialshavepermittedthemechanicaldesignertoproceedindirectionsthatwouldhavebeentotallyimpossibleonlyafewyearsago.Paralleldevelopmentinothertechnologiessuchaselectronicsandcomputershavemadeavailabletothemachinetooldesignermethodsandprocessesthatcanpermitamachinetooltofarexceedthecapabilitiesofthemostexperiencedmachinist.InthissectionwewilllookatCNCmachiningusingchipmakingcuttingtools.CNCcontrollersareusedtodriveandcontrolagreatvarietyofmachinesandmechanisms,Someexampleswouldberoutersinwoodworkinglasers,plasmaarc,flamecutting,andwaterjetsforcuttingofsteelplateandcontrollingofrobotsinmanufacturingandassembly.Thissectionisonlyanoverviewandcannottaketheplaceofaprogrammingmanualforaspecificmachinetool.Becauseofthetremendousgrowthinnumbersandcapabilityofcomputers,changesinmachinecontrolsarerapidlyandconstantlytakingplace.Theexcitingpartofthisevolutioninmachinecontrolsisthatprogrammingbecomeseasierwitheachnewadvancedinthistechnology.AdvantagesofNumericalControlAmanuallyoperatedmachinetoolmayhavethesamephysicalcharacteristicsasaCNCmachine,suchassizeandhorsepower.Theprinciplesofmetalremovalarethesame.Thebiggaincomesfromthecomputercontrollingthemachiningaxesmovements.CNCcontrolledmachinetoolscanbeassimpleasa2axisdrillingmachiningcenterFigureO1.Withadualspindlemachiningcenter,thelowRPM,highhorsepowerspindlegiveshighmetalremovalrates.ThehighRPMspindleallowstheefficientuseofhighcuttingspeedtoolssuchasdiamondsandsmalldiametercuttersFigureO2.Thecuttingtoolsthatremovematerialsarestandardtoolssuchasmillingcutters,drills,boringtools,orlathetoolsdependingonthetypeofmachineused.Cuttingspeedsandfeedsneedtobecorrectasinanyothermachiningoperation.ThegreatestadvantageinCNCmachiningcomesfromtheunerringandrapidpositioningmovementspossible.ACNCmachinedoesdotstopattheendofacuttoplanitsnextmoveitdoesnotgetfatigueditiscapableofuninterruptedmachiningerrorfree,hourafterhour.Amachinetoolisproductiveonlywhileitismakingchips.Sincethechipmakingprocessiscontrolledbytheproperfeedsandspeeds,timesavingscanbeachievedbyfasterrapidfeedrates.Rapidfeedshaveincreasedfrom60to200to400andarenowoftenapproaching1000inchesperminuteIPM.Thesehighfeedratescanposeasafetyhazardtoanyonewithintheworkingenvelopeofthemachinetool.徐州工程学院毕业设计论文2ComplexcontouredshapeswereextremelydifficulttoproductpriortoCNCmachining.CNChasmadethemachiningoftheseshapeseconomicallyfeasible.Designchangesonapartarerelativelyeasytomakebychangingtheprogramthatdirectsthemachinetool.ACNCmachineproducespartswithhighdimensionalaccuracyandclosetoleranceswithouttakingextratimeorspecialprecautions,CNCmachinesgenerallyneedlesscomplexworkholdingfixtures,whichsavestimebygettingthepartsmachinedsooner.Onceaprogramisreadyandproductionparts,eachpartwilltakeexactlythesameamountoftimeasthepreviousone.Thisrepeatabilityallowsforaveryprecisecontrolofproductioncosts.AnotheradvantageofCNCmachiningistheeliminationoflargeinventoriespartscanbemachinedasneeds.Inconventionalproductionoftenagreatnumberofpartsmustbemadeatthesametimetobecosteffective.WithCNCevenonepiececanbemachinedeconomically.Inmanyinstances,aCNCmachinecanperforminonesetupthesameoperationsthatwouldrequireseveralconventionalmachines.WithmodernCNCmachinetoolsatrainedmachinistcanprogramandproductevenasingleparteconomically.CNCmachinetoolsareusedinsmallandlargemachiningfacilitiesandrangeinsizefromtabletopmodelstohugemachiningcenters.InafacilitywithmanyCNCtools,programmingisusuallydonebyCNCprogrammersawayfromtheCNCtools.ThemachinecontrolunitMCUonthemachineisthenusedmostlyforsmallprogramchangesorcorrections.ManufacturingwithCNCtoolsusuallyrequiresthreecategoriesofpersons.Thefirstistheprogrammer,whoisresponsiblefordevelopingmachinereadycode.Thenextpersoninvolvedisthesetupperson,wholoadstherawstorkintotheMCU,checksthatthecorrecttoolsareloaded,andmakesthefirstpart.Thethirdpersonisthemachineandunloadsthefinishedparts.Inasmallcompany,onepersonisexpectedtoperformallthreeofthesetasks.CNCcontrolsaregenerallydividedintotwobasiccategories.OneusesawardaddressformatwithcodedinputssuchasGandMcodes.Theotherusersaconversationalinputconversationalinputisalsocalleduserfriendlyorpromptedinput.Laterinthissectionexamplesofeachoftheseprogrammingformatsinmachiningapplicationswillbedescribes.CAMandCNCCAMsystemshavechangedthejoboftheCNCprogrammerfromonemanuallyproducingCNCcodetoonemaximizingtheoutputofCNCmachines.SinceCNCmachinetoolsaremadebyagreatnumberofmanufacturers,manydifferentCNCcontrolunitsareinuse.Controlunitsfromdifferentmanufacturersuseavarietyofprogramformatsandcodes.ManyCNCcodewordsareidenticalfordifferentcontrollers,butagreatnumbervaryfromonetoanother.ToproduceanidenticalpartonCNCmachinetoolswithdifferentcontrollerssuchasonebyFANCU,OKUMAorDYNAPATH,wouldrequirecompletelydifferentCNCcodes.EachmanufacturerisconstantlyimprovingandupdatingitsCNCcontrollers.Theseimprovementsoftenincludeadditionalcodewordspluschangesinhowtheexistingcodeworks.ACAMsystemsallowstheCNCprogrammertoconcentrateonthecreationofanefficientmachiningprocess,ratherthenrelearningchangedcodeformats.ACNCprogrammerlooksat徐州工程学院毕业设计论文3theprintofapartandthenplansthesequenceofmachiningoperationsnecessarytomakeitFigureO3.Thisplanincludeseverything,fromtheselectionofpossibleCNCmachinetools,towhichtoolingtouse,tohowthepartisheldwhilemachiningtakesplace.TheCNCprogrammerhastohaveathoroughunderstandingofallthecapacitiesandlimitationsoftheCNCmachinetoolsthataprogramistobemadefor.Machinespecificationssuchashorsepower,maximumspindlespeeds,workpieceweightandsizelimitations,andtoolchangercapacityarejustsomeoftheconsiderationsthataffectprogramming.Anotherareaofmajorimportancetotheprogrammeristheknowledgeofmachiningprocesses.Anexamplewouldbetheselectionofthesurfacefinishrequirementspecifiedinthepartprint.Thesequenceofmachiningprocessesiscriticaltoobtainacceptableresults.Cuttingtoollimitationshavetobeconsideredandthisrequiresknowledgeofcuttingtoolmaterials,tooltypes,andapplicationrecommendations.Agoodprogrammerwillspendaconsiderableamountoftimeinresearchingtherapidlygrowingvolumeofnewandimprovedtoolsandtoolmaterials.Oftenthetoolthatwasonthecuttingedgeoftechnologyjusttwoyearsagoisnowobsolete.Informationonnewtoolscancomefromcatalogsortoolmanufacturerstoolingengineers.Helpintoolselectionoroptimumtoolworkingconditionscanalsobeobtainedfromtoolmanufacturersoftware.ExampleswouldbeKennametalsTOOLPRO,softwaredesignedtohelpselectthebesttoolgrade,speed,andfeedratesfordifferentworkmaterialsinturningapplication.AnotherveryimportantfeatureofTOOLPROisthedisplayofthehorsepowerrequirementforeachmachiningselection.Thisallowtheprogrammertoselectacombinationofcuttingspeed,feedrate,anddepthofcutthatequalsthemachinesmaximumhorsepowerforroughingcuts.Forafinishingcut,thesmallestdiameterofthepartbeingmachinedisselectedandthenthecuttingspeedvarieduntiltheRPMisequaltothemaximumRPMofthemachine.Thishelpsinmaximizingmachiningefficiency.Knowingthehorsepowerrequirementforacutiscriticalifmorethanonetooliscuttingatthesametime.SoftwareforamachiningcenterapplicationwouldbeIngersollToolCompanysActualChipThickness,aprogramusedtocalculatethechipthicknessinrelationtofeedpertoothforamillingcutter,especiallyduringashallowfinishingcut.IngersollsRigidityAnalysissoftwareealculatestooldeflectionforendmillsasafunctionoftoolstiffnessandtoolforce.Tothispointwelookedatsomegeneralqualificationsthataprogrammershouldpossess.NowweexaminehowaCAMsystemworks.PointControlCompanysSmartCamsystemusesthefollowingapproach.First,theprogrammermakesamentalmodeloftheparttobemachined.Thisincludesthekindofmachiningtobeperformedturningormilling.Thenthepartprintisstudiedtodevelopamachiningsequence,roughingandfinishingcuts,drilling,tapping,andboringoperations.Whatworkholdingdeviceistobeused,aviseorfixtureorclampsAftertheseconsiderations,computerinputcanbestarted.FirstcomesthecreationofaJOBPLAN.ThisJOBPLANconsistsofentriessuchasinchormetricunits,machinetype,partID,typeofworkpiecematerial,setupnotes,andadescriptionoftherequiredtools.Thislineofinformationdescribesthetoolbynumber,type,andsizeandincludesthe徐州工程学院毕业设计论文4appropriatecuttingspeedandfeedrate.Afteralltheselectedtoolsareentered,thefileissaved.Thesecondprogrammingstepisthemakingofthepart.Thisrepresentsagraphicmodelingoftheprojectedmachiningoperation.AfterselectingatoolfromthepreparedJOBPLAN,parametersforthecuttingoperationareentered.Foradrill,oncethecoordinatelocationoftheholeandthedeptharegiven,acircleappearsonthatspot.Ifthelocationisincorrect,theUNDOcommanderasesthisentryandallowsyoutogivenewvaluesforthisoperation.Whenanendmillisbeingused,cuttingmovementstoolpathareusuallydefinedaslinesandarcs.Asalineisprogrammed,thetoolpathisgraphicallydisplayedanderrorscanbecorrectedinstantly.Atanytimeduringprogramming,thecommandSHOWPATHwillshowtheactualtoolpathforeachoftheprogrammedtools.Thetoolswillbedisplayedinthesequenceinwhichtheywillbeusedduringactualmachining.Ifthesequenceofatoolmovementneedstobechanged,afewkeystrokeswilltothat.SometimesinCAMtheprogrammingsequenceisdifferentfromtheactualmachiningorder.Anexamplewouldbethemachiningofapocketinapart.WithCAM,thefinishedpocketoutlineisprogrammedfirst,thenthisoutlineisusedtodefinetheroughingcutstomachinethepocket.Theroughingcutsarecomputergeneratedfrominputssuchasdepthandwidthofcutandhowmuchmaterialtoleaveforthefinishcut.Differentroughingpatternscanbetriedouttoallowtheprogrammertoselectthemostefllcientonefortheactualmachiningcuts.Sinceeachtoolisrepresentedbyadifferentcolor,itiseasytoobservethetoolpathmadebyeachone.ACAMsystemletstheprogrammerviewthegraphicsmodelfromvaryingangles,suchasatop,front,side,orisometricview.Atoolpaththatlookscorrectfromatopview,mayshowfromafrontviewthatthedepthofthecuttingtoolisincorrect.Changescaneasilybemadeandseenimmediately.Whenthetoolpathandthesequenceofoperationsaresatisfactory,machinereadycodehastobemade.ThisisaseasyasspecifyingtheCNCmachinethatistobeusedtomachinethepart.ThecodegeneratorforthatspecificCNCmachineduringprocessingaccessesfourdifferentfiles.TheJOBPLANfileforthetoolinformationandtheGRAPHICEfileforthetoolpathandcuttingsequence.ItalsousestheMACHINEDEFINEfilewhichdefinestheCNCcodewordsforthatspecificmachine.Thisfilealsosuppliesdataformaximumfeedrates,RPM,toolchangetimes,andsoon.ThefourthfiletakingpartinthecodegeneratingprocessistheTEMPLATEfile.ThisfileactslikearulerthatproducestheCNCcodewithallofitspartsintherightplaceandsequence.Whenthecodegenerationiscomplete,aprojectedmachiningtimeisdisplayed.Thistimeiscalculatedfromvaluessuchasfeedratesanddistancestraveled,noncuttingmovementsatmaximumfeedratesbetweenpoints,toolchangetimes,andsoon.Theprojectedmachiningtimecanberevisedbychangingtoolingtoallowforhighermetalremovalratesorcreatingamoreefficienttoolpath.Thisdisplayoftotaltimerequiredcanalsobeusedtoestimateproductioncosts.IfmorethenoneCNCmachinetoolisavailabletomachinethispart,makingcodeandcomparingthemachiningtimemayshowthatonemachineismoreefficientthantheothers.
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