半閉環(huán)數(shù)控車床總體設(shè)計(jì)【含3張CAD圖紙】
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英文原文CNC machine toolsWhilethespecificintentionandapplicationforCNCmachinesvaryfromonemachinetype toanother,allformsofCNChavecommonbenefits.Herearebutafewofthemoreimportant benefitsofferedbyCNCequipment.ThefirstbenefitofferedbyallformsofCNCmachinetoolsisimprovedautomation. The operatorinterventionrelatedtoproducingworkpiecescanbereducedoreliminated.ManyCNCmachinescanrununattendedduringtheirentiremachiningcycle,freeingtheoperatortodoother tasks.ThisgivestheCNCuserseveralsidebenefitsincludingreducedoperatorfatigue,fewer mistakescausedbyhumanerror,andconsistentandpredictablemachiningtimeforeach workpiece.Sincethemachinewillberunningunderprogramcontrol,theskilllevelrequiredof theCNCoperator(relatedtobasicmachiningpractice)isalsoreducedascomparedtoamachinistproducingworkpieceswithconventionalmachinetools.ThesecondmajorbenefitofCNCtechnologyisconsistentandaccurateworkpieces.TodaysCNCmachinesboastalmostunbelievableaccuracyandrepeatabilityspecifications.Thismeans thatonceaprogramisverified,two,ten,oronethousandidenticalworkpiecescanbeeasily producedwithprecisionandconsistency.AthirdbenefitofferedbymostformsofCNCmachinetoolsisflexibility.Sincethese machinesarerunfromprograms,runningadifferentworkpieceisalmostaseasyasloadinga differentprogram.Onceaprogramhasbeenverifiedandexecutedforoneproductionrun,itcan beeasilyrecalledthenexttimetheworkpieceistoberun.Thisleadstoyetanotherbenefit,fast changeover.Sincethesemachinesareveryeasytosetupandrun,andsinceprogramscanbe easilyloaded,theyallowveryshortsetuptime.Thisisimperativewithtodaysjust-in-time(JIT) product requirements.Motioncontrol-theheartofCNCThemostbasicfunctionofanyCNCmachineisautomatic,precise,andconsistentmotion control.Ratherthanapplyingcompletelymechanicaldevicestocausemotionasisrequiredon mostconventionalmachinetools,CNCmachinesallowmotioncontrolinarevolutionarymanner2.AllformsofCNCequipmenthavetwoormoredirectionsofmotion,calledaxes.Theseaxes canbepreciselyandautomaticallypositionedalongtheirlengthsoftravel.Thetwomostcommonaxistypesarelinear(drivenalongastraightpath)androtary(drivenalongacircularpath).Insteadofcausingmotionbyturningcranksandhandwheelsasisrequiredonconventionalmachinetools,CNCmachinesallowmotionstobecommandedthroughprogrammedcommands.Generallyspeaking,themotiontype(rapid,linear,andcircular),theaxestomove,theamountofmotionandthemotionrate(feedrate)areprogrammablewithalmostallCNCmachinetools.ACNCcommandexecutedwithinthecontroltellsthedrivemotortorotateaprecisenumberoftimes.Therotationofthedrivemotorinturnrotatestheballscrew.Andtheballscrewdrives thelinearaxis(slide).Afeedbackdevice(linearscale)ontheslideallowsthecontroltoconfirm thatthecommandednumberofrotationshastakenplace3. Thougharathercrudeanalogy,thesamebasiclinearmotioncanbefoundonacommontablevise.Asyourotatethevisecrank,yourotatealeadscrewthat,inturn,drivesthemovablejawonthevise.Bycomparison,alinearaxisonaCNCmachinetoolisextremelyprecise.Thenumberofrevolutionsoftheaxisdrivemotorpreciselycontrolstheamountoflinearmotionalongtheaxis.Howaxismotioniscommanded-understandingcoordinatesystems.ItwouldbeinfeasiblefortheCNCusertocauseaxismotionbytryingtotelleachaxisdrivemotorhowmanytimestorotateinordertocommandagivenlinearmotionamount4.(Thiswouldbelikehavingtofigureouthowmanyturnsofthehandleonatablevisewillcausethemovable jawtomoveexactlyoneinch!)Instead,allCNCcontrolsallowaxismotiontobecommandedinamuchsimplerandmorelogicalwaybyutilizingsomeformofcoordinatesystem.Thetwomost popularcoordinatesystemsusedwithCNCmachinesaretherectangularcoordinatesystemand thepolarcoordinatesystem.Byfar,themorepopularofthesetwoistherectangularcoordinate system.TheprogramzeropointestablishesthepointofreferenceformotioncommandsinaCNC program.Thisallowstheprogrammertospecifymovementsfromacommonlocation.Ifprogramzeroischosenwisely,usuallycoordinatesneededfortheprogramcanbetakendirectlyfromtheprint.Withthistechnique,iftheprogrammerwishesthetooltobesenttoapositiononeinchtotherightoftheprogramzeropoint,X1.0iscommanded.Iftheprogrammerwishesthetooltomovetoapositiononeinchabovetheprogramzeropoint,Y1.0iscommanded.Thecontrolwill automaticallydeterminehowmanytimestorotateeachaxisdrivemotorandballscrewtomake theaxisreachthecommandeddestinationpoint.Thisletstheprogrammercommandaxismotioninaverylogicalmanner.Alldiscussionstothispointassumethattheabsolutemodeofprogrammingisused.ThemostcommonCNCwordusedtodesignatetheabsolutemodeisG90.Intheabsolutemode,theendpointsforallmotionswillbespecifiedfromtheprogramzeropoint.Forbeginners,thisisusuallythebestandeasiestmethodofspecifyingendpointsformotioncommands.However,thereisanotherwayofspecifyingendpointsforaxismotion.Intheincrementalmode(commonlyspecifiedbyG91),endpointsformotionsarespecifiedfromthetoolscurrentposition,notfromprogramzero.Withthismethodofcommandingmotion,theprogrammermustalwaysbeaskingHowfarshouldImovethetool?Whiletherearetimeswhentheincrementalmodecanbeveryhelpful,generallyspeaking,thisisthemorecumbersomeanddifficultmethodofspecifyingmotionandbeginnersshouldconcentrateonusingtheabsolutemode.Becarefulwhenmakingmotioncommands.Beginnershavethetendencytothinkincrementally.Ifworkingintheabsolutemode(asbeginnersshould),theprogrammershouldalwaysbeaskingTowhatpositionshouldthetoolbemoved?Thispositionisrelativetoprogramzero,NOTfromthetoolscurrentposition.Asidefrommakingitveryeasytodeterminethecurrentpositionforanycommand,anotherbenefitofworkingintheabsolutemodehastodowithmistakesmadeduringmotioncommands.Intheabsolutemode,ifamotionmistakeismadeinonecommandoftheprogram,onlyonemovementwillbeincorrect.Ontheotherhand,ifamistakeismadeduringincrementalmovements,allmotionsfromthepointofthemistakewillalsobeincorrect.AssigningprogramzeroKeepinmindthattheCNCcontrolmustbetoldthelocationoftheprogramzeropointbyonemeansoranother.HowthisisdonevariesdramaticallyfromoneCNCmachineandcontroltoanother8.One(older)methodistoassignprogramzerointheprogram.Withthismethod,theprogrammertellsthecontrolhowfaritisfromtheprogramzeropointtothestartingpositionofthemachine.ThisiscommonlydonewithaG92(orG50)commandatleastatthebeginningoftheprogramandpossiblyatthebeginningofeachtool.Another,newerandbetterwaytoassignprogramzeroisthroughsomeformofoffset.Refertofig.4.Commonlymachiningcentercontrolmanufacturerscalloffsetsusedtoassignprogramzerofixtureoffsets.Turningcentermanufacturerscommonlycalloffsetsusedtoassignprogramzeroforeachtoolgeometryoffsets.Aflexiblemanufacturingcell(FMC)canbeconsideredasaflexiblemanufacturingsubsystem.ThefollowingdifferencesexistbetweentheFMCandtheFMS:1. AnFMCisnotunderthedirectcontrolofthecentralcomputer.Instead,instructionsfromthecentralcomputerarepassedtothecellcontroller.2. Thecellislimitedinthenumberofpartfamiliesitcanmanufacture.ThefollowingelementsarenormallyfoundinanFMC:CellcontrollerProgrammablelogiccontroller(PLC)MorethanonemachinetoolAmaterialshandlingdevice(robotorpallet)TheFMCexecutesfixedmachiningoperationswithpartsflowingsequentiallybetweenoperations.HighspeedmachiningThetermHighSpeedMachining(HSM)commonlyreferstoendmillingathighrotationalspeedsandhighsurfacefeeds.Forinstance,theroutingofpocketsinaluminumairframesectionswithaveryhighmaterialremovalrate1.Overthepast60years,HSMhasbeenappliedtoawiderangeofmetallicandnon-metallicworkpiecematerials,includingtheproductionofcomponentswithspecificsurfacetopographyrequirementsandmachiningofmaterialswithhardnessof50HRCandabove.Withmoststeelcomponentshardenedtoapproximately32-42HRC,machiningoptionscurrentlyinclude:Roughmachiningandsemi-finishingofthematerialinitssoft(annealed)conditionheattreatmenttoachievethefinalrequiredhardness=63HRCmachiningofelectrodesandElectricalDischargeMachining(EDM)ofspecificpartsofdiesandmoulds(specificallysmallradiianddeepcavitieswithlimitedaccessibilityformetalcuttingtools)finishingandsuper-finishingofcylindrical/flat/cavitysurfaceswithappropriatecementedcarbide,cermet,solidcarbide,mixedceramicorpolycrystallinecubicboronnitride(PCBN)Formanycomponents,theproductionprocessinvolvesacombinationoftheseoptionsandinthecaseofdiesandmouldsitalsoincludestimeconsuminghandfinishing.Consequently,productioncostscanbehighandleadtimesexcessive.Itistypicalinthedieandmouldindustrytoproduceoneorjustafewtoolsofthesamedesign.Theprocessinvolvesconstantchangestothedesign,andbecauseofthesechangesthereisalsoacorrespondingneedformeasuringandreverseengineering.Themaincriteriaisthequalitylevelofthedieormouldregardingdimensional,geometricandsurfaceaccuracy.Ifthequalitylevelaftermachiningispoorandifitcannotmeettherequirements,therewillbeavaryingneedofmanualfinishingwork.Thisworkproducessatisfactorysurfaceaccuracy,butitalwayshasanegativeimpactonthedimensionalandgeometricaccuracy.Oneofthemainaimsforthedieandmouldindustryhasbeen,andstillis,toreduceoreliminatetheneedformanualpolishingandthusimprovethequalityandshortentheproductioncostsandleadtimes.MaineconomicalandtechnicalfactorsforthedevelopmentofHSMSurvivalTheeverincreasingcompetitioninthemarketplaceiscontinuallysettingnewstandards.Thedemandsontimeandcostefficiencyisgettinghigherandhigher.Thishasforcedthedevelopmentofnewprocessesandproductiontechniquestotakeplace.HSM provideshopeandsolutions.MaterialsThedevelopmentofnew,moredifficulttomachinematerialshasunderlinedthenecessitytofindnewmachiningsolutions.Theaerospaceindustryhasitsheatresistantandstainlesssteelalloys.Theautomotiveindustryhasdifferentbimetalcompositions,CompactGraphiteIronandaneverincreasingvolumeofaluminum3.Thedieandmouldindustrymainlyhastofacetheproblemofmachininghighhardenedtoolsteels,fromroughingtofinishing.QualityThedemandforhighercomponentorproductqualityistheresultofeverincreasingcompetition.HSM,ifappliedcorrectly,offersanumberofsolutionsinthisarea.Substitutionofmanualfinishingisoneexample,whichisespeciallyimportantondiesandmouldsorcomponentswithacomplex3Dgeometry.ProcessesThedemandsonshorterthroughputtimesviafewersetupsandsimplifiedflows(logistics)caninmostcases,besolvedbyHSM.Atypicaltargetwithinthedieandmouldindustryistocompletelymachinefullyhardenedsmallsizedtoolsinonesetup.CostlyandtimeconsumingEDMprocessescanalsobereducedoreliminatedwithHSM.Design&developmentOneofthemaintoolsintodayscompetitionistosellproductsonthevalueofnovelty.Theaverageproductlifecycleoncarstodayis4years,computersandaccessories1.5years,handphones3months.OneoftheprerequisitesofthisdevelopmentoffastdesignchangesandrapidproductdevelopmenttimeistheHSMtechnique.ComplexproductsThereisanincreaseofmulti-functionalsurfacesoncomponents,suchasnewdesignofturbinebladesgivingnewandoptimizedfunctionsandfeatures.Earlierdesignsallowedpolishingbyhandorwithrobots(manipulators).Turbinebladeswithnew,moresophisticateddesignshavetobefinishedviamachiningandpreferablybyHSM.Therearealsomoreandmoreexamplesofthinwalledworkpiecesthathavetobemachined(medicalequipment,electronics,productsfordefence,computerparts)ProductionequipmentThestrongdevelopmentofcuttingmaterials,holdingtools,machinetools,control sandespeciallyCAD/CAMfeaturesandequipment,hasopenedpossibilitiesthatmustbemetwithnewproductionmethodsandtechniques5.DefinitionofHSMSalomonstheory,Machiningwithhighcuttingspeeds.onwhich,in1931,tookoutaGermanpatent,assumesthatatacertaincuttingspeed(5-10timeshigherthaninconventionalmachining),thechipremovaltemperatureatthecuttingedgewillstarttodecrease.Giventheconclusion:.seemstogiveachancetoimproveproductivityinmachiningwithconventionaltoolsathighcuttingspeeds.Modernresearch,unfortunately,hasnotbeenabletoverifythistheorytotally.Thereisarelativedecreaseofthetemperatureatthecuttingedgethatstartsatcertaincuttingspeedsfordifferentmaterials.Thedecreaseissmallforsteelandcastiron.Butlargerforaluminumandothernon-ferrousmetals.ThedefinitionofHSMmustbebasedonotherfactors.Giventodaystechnology,highspeedisgenerallyacceptedtomeansurfacespeedsbetween1and10kilometersperminuteorroughly3300to33000feetperminute.Speedsabove10km/minareintheultra-highspeedcategory,andarelargelytherealmofexperimentalmetalcutting.Obviously,thespindlerotationsrequiredtoachievethesesurfacecuttingspeedsaredirectlyrelatedtothediameterofthetoolsbeingused.Onetrendwhichisveryevidenttodayistheuseofverylargecutterdiametersfortheseapplications-andthishasimportantimplicationsfortooldesign.Therearemanyopinions,manymythsandmanydifferentwaystodefineHSM.MaintenanceandtroubleshootingMaintenanceforahorizontalMCThefollowingisalistofrequiredregularmaintenanceforaHorizontalMachiningCenterasshowninfig.5.Listedarethefrequencyofservice,capacities,andtypeoffluidsrequired.Theserequiredspecificationsmustbefollowedinordertokeepyourmachineingoodworkingorderandprotectyourwarranty.DailyTopoffcoolantleveleveryeighthourshift(especiallyduringheavyTSCusage).Checkwaylubelubricationtanklevel.Cleanchipsfromwaycoversandbottompan.Cleanchipsfromtoolchanger.Wipespindletaperwithacleanclothragandapplylightoil.WeeklyCheckforproperoperationofautodrainonfilterregulator.OnmachineswiththeTSCoption,cleanthechipbasketonthecoolanttank.Removethetankcoverandremoveanysedimentinsidethetank.BecarefultodisconnectthecoolantpumpfromthecontrollerandPOWEROFFthecontrolbeforeworkingonthecoolanttank.DothismonthlyformachineswithouttheTSCoption.Checkairgauge/regulatorfor85psi.FormachineswiththeTSCoption,placeadabofgreaseontheV-flangeoftools.DothismonthlyformachineswithouttheTSCoption.Cleanexteriorsurfaceswithmildcleaner.DONOTusesolvents.Checkthehydrauliccounterbalancepressureaccordingtothemachinesspecifications.Placeadabofgreaseontheoutsideedgeofthefingersofthetoolchangerandrunthroughalltools.MonthlyCheckoillevelingearbox.Addoiluntiloilbeginsdrippingfromoverflowtubeatbottomofsumptank.Cleanpadsonbottomofpallets.CleanthelocatingpadsontheA-axisandtheloadstation.Thisrequiresremovingthepallet.Inspectwaycoversforproperoperationandlubricatewithlightoil,ifnecessary.SixmonthsReplacecoolantandthoroughlycleanthecoolanttank.Checkallhosesandlubricationlinesforcracking.AnnuallyReplacethegearboxoil.Draintheoilfromthegearbox,andslowlyrefillitwith2quartsofMobilDTE25oil.Checkoilfilterandcleanoutresidueatbottomforthelubricationchart.Replaceairfilteroncontrolboxevery2years.Mineralcuttingoilswilldamagerubberbasedcomponentsthroughoutthemachine.TroubleshootingThissectionisintendedforuseindeterminingthesolutiontoaknownproblem.SolutionsgivenareintendedtogivetheindividualservicingtheCNCapatterntofollowin,first,determiningtheproblemssourceand,second,solvingtheproblem.UsecommonsenseManyproblemsareeasilyovercomebycorrectlyevaluatingthesituation.Allmachineoperationsarecomposedofaprogram,tools,andtooling.Youmustlookatallthreebeforeblamingoneasthefaultarea.Ifaboredholeischatteringbecauseofanoverextendedboringbar,dontexpectthemachinetocorrectthefault.Dontsuspectmachineaccuracyifthevisebendsthepart.Dontclaimholemis-positioningifyoudontfirstcenter-drillthehole.FindtheproblemfirstManymechanicstearintothingsbeforetheyunderstandtheproblem,hopingthatitwillappearastheygo.Weknowthisfromthefactthatmorethanhalfofallwarrantyreturnedpartsareingoodworkingorder.Ifthespindledoesntturn,rememberthatthespindleisconnectedtothegearbox,whichisconnectedtothespindlemotor,whichisdrivenbythespindledrive,whichisconnectedtotheI/OBOARD,whichisdrivenbytheMOCON,whichisdrivenbytheprocessor.Themoralhereisdontreplacethespindledriveifthebeltisbroken.Findtheproblemfirst;dontjustreplacetheeasiestparttogetto.DontinkerwiththemachineTherearehundredsofparameters,wires,switches,etc.,thatyoucanchangeinthismachine.Dontstartrandomlychangingpartsandparameters.Remember,thereisagoodchancethatifyouchangesomething,youwillincorrectlyinstallitorbreaksomethingelseintheprocess6.Considerforamomentchangingtheprocessorsboard.First,youhavetodownloadallparameters,removeadozenconnectors,replacetheboard,reconnectandreload,andifyoumakeonemistakeorbendonetinypinitWONTWORK.Youalwaysneedtoconsidertheriskofaccidentallydamagingthemachineanytimeyouworkonit.Itischeapinsurancetodouble-checkasuspectpartbeforephysicallychangingit.Thelessworkyoudoonthemachinethebetter. 中文譯文數(shù)控機(jī)床 雖然各種數(shù)控機(jī)床的功能和應(yīng)用各不相同,但它們有著共同的優(yōu)點(diǎn)。這里是數(shù)控設(shè)備提供的比較重要的幾個(gè)優(yōu)點(diǎn)。 各種數(shù)控機(jī)床的第一個(gè)優(yōu)點(diǎn)是自動(dòng)化程度提高了。零件制造過程中的人為干預(yù)減少或者免除了。整個(gè)加工循環(huán)中,很多數(shù)控機(jī)床處于無人照看狀態(tài),這使操作員被解放出來,可以干別的工作。數(shù)控機(jī)床用戶得到的幾個(gè)額外好處是:數(shù)控機(jī)床減小了操作員的疲勞程度,減少了人為誤差,工件加工時(shí)間一致而且可預(yù)測。由于機(jī)床在程序的控制下運(yùn)行,與操作普通機(jī)床的機(jī)械師要求的技能水平相比,對(duì)數(shù)控操作員的技能水平要求(與基本加工實(shí)踐相關(guān))也降低了。 數(shù)控技術(shù)的第二個(gè)優(yōu)點(diǎn)是工件的一致性好,加工精度高?,F(xiàn)在的數(shù)控機(jī)床宣稱的精度以及重復(fù)定位精度幾乎令人難以置信。這意味著,一旦程序被驗(yàn)證是正確的,可以很容易地加工出2個(gè)、10個(gè)或1000個(gè)相同的零件,而且它們的精度高,一致性好。大多數(shù)數(shù)控機(jī)床的第三個(gè)優(yōu)點(diǎn)是柔性強(qiáng)。由于這些機(jī)床在程序的控制下工作,加工不同的工件易如在數(shù)控系統(tǒng)中裝載一個(gè)不同的程序而己。一旦程序驗(yàn)證正確,并且運(yùn)行一次,下次加工工件的時(shí)候,可以很方便地重新調(diào)用程序。這又帶來另一個(gè)好處可以快速切換不同工件的加工。由于這些機(jī)床很容易調(diào)整并運(yùn)行,也由于很容易裝載加工程序,因此機(jī)床的調(diào)試時(shí)間很短。這是當(dāng)今準(zhǔn)時(shí)生產(chǎn)制造模式所要求的。 任何數(shù)控機(jī)床最基本的功能是具有自動(dòng)、精確、一致的運(yùn)動(dòng)控制。大多數(shù)普通機(jī)床完全運(yùn)用機(jī)械裝置實(shí)現(xiàn)其所需的運(yùn)動(dòng),而數(shù)控機(jī)床是以一種全新的方式控制機(jī)床的運(yùn)動(dòng)。各種數(shù)控設(shè)備有兩個(gè)或多個(gè)
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