编号:95454
类型:共享资源
大小:50KB
格式:DOC
上传时间:2013-11-17
上传人:英****
认证信息
个人认证
方**(实名认证)
江苏
IP属地:江苏
6
积分
- 关 键 词:
-
教育专区
外文翻译
精品文档
中英文翻
- 资源描述:
-
CNCcontrolandcuttingLathesaremachinetoolsdesignedprimarilytodoturning,facingandboring,Verylittleturningisdoneonothertypesofmachinetools,andnonecandoitwithequalfacility.Becauselathesalsocandodrillingandreaming,theirversatilitypermitsseveraloperationstobedonewithasinglesetupoftheworkpiece.Consequently,morelathesofvarioustypesareusedinmanufacturingthananyothermachinetool.Theessentialcomponentsofalathearethebed,headstockassembly,tailstockassembly,andtheleadscrewandfeedrod.Thebedisthebackboneofalathe.Itusuallyismadeofwellnormalizedoragedgrayornodularcastironandprovidessheavy,rigidframeonwhichalltheotherbasiccomponentsaremounted.Twosetsofparallel,longitudinalways,innerandouter,arecontainedonthebed,usuallyontheupperside.SomemakersuseaninvertedV-shapeforallfourways,whereasothersutilizeoneinvertedVandoneflatwayinoneorbothsets,Theyareprecision-machinedtoassureaccuracyofalignment.Onmostmodernlathesthewayaresurface-hardenedtoresistwearandabrasion,butprecautionshouldbetakeninoperatingalathetoassurethatthewaysarenotdamaged.Anyinaccuracyinthemusuallymeansthattheaccuracyoftheentirelatheisdestroyed.Theheadstockismountedinafoxedpositionontheinnerways,usuallyattheleftendofthebed.Itprovidesapoweredmeansofrotatingthewordatvariousspeeds.Essentially,itconsistsofahollowspindle,mountedinaccuratebearings,andasetoftransmissiongears-similartoatrucktransmission—throughwhichthespindlecanberotatedatanumberofspeeds.Mostlathesprovidefrom8to18speeds,usuallyinageometricratio,andonmodernlathesallthespeedscanbeobtainedmerelybymovingfromtwotofourlevers.Anincreasingtrendistoprovideacontinuouslyvariablespeedrangethroughelectricalormechanicaldrives.Becausetheaccuracyofalatheisgreatlydependentonthespindle,itisofheavyconstructionandmountedinheavybearings,usuallypreloadedtaperedrollerorballtypes.Thespindlehasaholeextendingthroughitslength,throughwhichlongbarstockcanbefed.Thesizeofmaximumsizeofbarstockthatcanbemachinedwhenthematerialmustbefedthroughspindle.Thetailsticdassemblyconsists,essentially,ofthreeparts.Alowercastingfitsontheinnerwaysofthebedandcanslidelongitudinallythereon,withameansforclampingtheentireassemblyinanydesiredlocation,Anuppercastingfitsontheloweroneandcanbemovedtransverselyuponit,onsometypeofkeyedways,topermitaligningtheassemblyisthetailstockquill.Thisisahollowsteelcylinder,usuallyabout51to76mm(2to3inches)indiameter,thatcanbemovedseveralincheslongitudinallyinandoutoftheuppercastingbymeansofahandwheelandscrew.Thesizeofalatheisdesignatedbytwodimensions.Thefirstisknownastheswing.Thisisthemaximumdiameterofworkthatcanberotatedonalathe.Itisapproximatelytwicethedistancebetweenthelineconnectingthelathecentersandthenearestpointontheways,Thesecondsizedimensionisthemaximumdistancebetweencenters.Theswingthusindicatesthemaximumworkpiecediameterthatcanbeturnedinthelathe,whilethedistancebetweencentersindicatesthemaximumlengthofworkpiecethatcanbemountedbetweencenters.Enginelathesarethetypemostfrequentlyusedinmanufacturing.Theyareheavy-dutymachinetoolswithallthecomponentsdescribedpreviouslyandhavepowerdriveforalltoolmovementsexceptonthecompoundrest.Theycommonlyrangeinsizefrom305to610mm(12to24inches)swingandfrom610to1219mm(24to48inches)centerdistances,butswingsupto1270mm(50inches)andcenterdistancesupto3658mm(12feet)arenotuncommon.Mosthavechippansandabuilt-incoolantcirculatingsystem.Smallerenginelathes-withswingsusuallynotover330mm(13inches)–alsoareavailableinbenchtype,designedforthebedtobemountedonabenchonabenchorcabinet.Althoughenginelathesareversatileandveryuseful,becauseofthetimerequiredforchangingandsettingtoolsandformakingmeasurementsontheworkpiece,thyarenotsuitableforquantityproduction.Oftentheactualchip-productiontineislessthan30%ofthetotalcycletime.Inaddition,askilledmachinistisrequiredforalltheoperations,andsuchpersonsarecostlyandofteninshortsupply.However,muchoftheoperator’stimeisconsumedbysimple,repetitiousadjustmentsandinwatchingchipsbeingmade.Consequently,toreduceoreliminatetheamountofskilledlaborthatisrequired,turretlathes,screwmachines,andothertypesofsemiautomaticandautomaticlatheshavebeenhighlydevelopedandarewidelyusedinmanufacturing.2NumericalControlOneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol(NC).PriortotheadventofNC,allmachinetoolseremanuallyoperatedandcontrolled.Amongthemanylimitationsassociatedwithmanualcontrolmachinetools,perhapsnoneismoreprominentthanthelimitationofoperatorskills.Withmanualcontrol,thequalityoftheproductisdirectlyrelatedtoandlimitedtotheskillsoftheoperator.Numericalcontrolrepresentsthefirstmajorstepawayfromhumancontrolofmachinetools.Numericalcontrolmeansthecontrolofmachinetoolsandothermanufacturingsystemsthroughtheuseofprerecorded,writtensymbolicinstructions.Ratherthanoperatingamachinetool,anNCtechnicianwritesaprogramthatissuesoperationalinstructionstothemachinetool.Foramachinetooltobenumericallycontrolled,itmustbeinterfacedwithadeviceforacceptinganddecodingtheprogrammedinstructions,knownasareader.Numericalcontrolwasdevelopedtoovercomethelimitationofhumanoperators,andithasdoneso.Numericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelong-runtoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentofseveralotherinnovationsinmanufacturingtechnology:Electricaldischargemachining,Lasercutting,Electronbeamwelding.Numericalcontrolhasalsomademachinetoolsmoreversatilethantheirmanuallyoperatedpredecessors.AnNCmachinetoolcanautomaticallyproduceawideofparts,eachinvolvinganassortmentofwidelyvariedandcomplexmachiningprocesses.Numericalcontrolhasallowedmanufacturerstoundertaketheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetollsandprocesses.Likesomanyadvancedtechnologies,NCwasborninthelaboratoriesoftheMassachusettsInstituteofTechnology.TheconceptofNCwasdevelopedintheearly1950swithfundingprovidedbytheU.S.AirForce.Initsearlieststages,NCmachineswereabletomadestraightcutsefficientlyandeffectively.However,curvedpathswereaproblembecausethemachinetoolhadtobeprogrammedtoundertakeaseriesofhorizontalandverticalstepstoproduceacurve.Theshorterthestraightlinesmakingupthesteps,thesmootheristhecurve,Eachlinesegmentinthestepshadtobecalculated.Thisproblemledtothedevelopmentin1959oftheAutomaticallyProgrammedTools(APT)language.ThisisaspecialprogramminglanguageforNCthatusesstatementssimilartoEnglishlanguagetodefinethepartgeometry,describethecuttingtoolconfiguration,andspecifythenecessarymotions.ThedevelopmentoftheAPTlanguagewasamajorstepforwardinthefurtherdevelopmentfromthoseusedtoday.Themachineshadhardwiredlogiccircuits.Theinstructionalprogramswerewrittenonpunchedpaper,whichwaslatertobereplacedbymagneticplastictape.Atapereaderwasusedtointerprettheinstructionswrittenonthetapeforthemachine.Together,allofthisrepresentedagiantstepforwardinthecontrolofmachinetools.However,therewereanumberofproblemswithNCatthispointinitsdevelopment.Amajorproblemwasthefragilityofthepunchedpapertapemedium.Itwascommonforthepapertapecontainingtheprogrammedinstructionstobreakortearduringamachiningprocess.Thisproblemwasexacerbatedbythefactthateachsuccessivetimeapartwasproducedonamachinetool,thepapertapecarryingtheprogrammedinstructionshadtobererunthroughthereader.Ifitwasnecessarytoproduce100copiesofagivenpart,itwasalsonecessarytorunthepapertapethroughthereader100separatetines.Fragilepapertapessimplycouldnotwithstandtherigorsofashopfloorenvironmentandthiskindofrepeateduse.Thisledtothedevelopmentofaspecialmagneticplastictape.Whereasthepapercarriedtheprogrammedinstructionsasaseriesofholespunchedinthetape,theplastictapecarriedtheinstructionsasaseriesofmagneticdots.Theplastictapewasmuchstrongerthanthepapertape,whichsolvedtheproblemoffrequenttearingandbreakage.However,itstilllefttwootherproblems.Themostimportantofthesewasthatitwasdifficultorimpossibletochangetheinstructionsenteredonthetape.Tomadeeventhemostminoradjustmentsinaprogramofinstructions,itwasnecessarytointerruptmachiningoperationsandmakeanewtape.Itwasalsostillnecessarytorunthetapethroughthereaderasmanytimesastherewerepartstobeproduced.Fortunately,computertechnologybecamearealityandsoonsolvedtheproblemsofNCassociatedwithpunchedpaperandplastictape.Thedevelopmentofaconceptknownasdirectnumericalcontrol(DNC)solvedthepaperandplastictapeproblemsassociatedwithnumericalcontrolbysimplyeliminatingtapeasthemediumforcarryingtheprogrammedinstructions.Indirectnumericalcontrol,machinetoolsaretied,viaadatatransmissionlink,toahostcomputer.Programsforoperatingthemachinetoolsarestoredinthehostcomputerandfedtothemachinetoolanneededviathedatatransmissionlinkage.Directnumericalcontrolrepresentedamajorstepforwardoverpunchedtapeandplastictape.However,itissubjecttothesamelimitationsasalltechnologiesthatdependonahostcomputer.Whenthehostcomputergoesdown,themachinetoolsalsoexperiencedowntime.Thisproblemledtothedevelopmentofcomputernumericalcontrol.3TurningTheenginelathe,oneoftheoldestmetalremovalmachines,hasanumberofusefulandhighlydesirableattributes.Todaytheselathesareusedprimarilyinsmallshopswheresmallerquantitiesratherthanlargeproductionrunsareencountered.Theenginelathehasbeenreplacedintoday’sproductionshopsbyawidevarietyofautomaticlathessuchasautomaticofsingle-pointtoolingformaximummetalremoval,andtheuseofformtoolsforfinishonaparwiththefastestprocessingequipmentonthescenetoday.Tolerancesfortheenginelathedependprimarilyontheskilloftheoperator.Thedesignengineermustbecarefulinusingtolerancesofanexperimentalpartthathasbeenproducedontheenginelathebyaskilledoperator.Inredesigninganexperimentalpartforproduction,economicaltolerancesshouldbeused.TurretLathesProductionmachiningequipmentmustbeevaluatednow,morethaneverbefore,thiscriterionforestablishingtheproductionqualificationofaspecificmethod,theturretlathemeritsahighrating.Indesigningforlowquantitiessuchas100or200parts,itismosteconomicaltousetheturretlathe.Inachievingtheoptimumtolerancespossibleontheturretslathe,thedesignershouldstriveforaminimumofoperations.AutomaticScrewMachinesGenerally,automaticscrewmachinesfallintoseveralcategories;single-spindleautomatics,multiple-spindleautomaticsandautomaticchuckingmachines.Originallydesignedforrapid,automaticproductionofscrewsandsimilarthreadedparts,theautomaticscrewmachinehaslongsinceexceededtheconfinesofthisnarrowfield,andtodayplaysavitalroleinthemassproductionofavarietyofprecisionparts.Quantitiesplayanimportantpartintheeconomyofthepartsmachinedontheautomaticscrewmachine.Quantitieslessthanontheautomaticscrewmachine.Thecostofthepartsmachinedcanbereducediftheminimumeconomicallotsizeiscalculatedandthepropermachineisselectedforthesequantities.AutomaticTracerLathesSincesurfaceroughnessdependsgreatlyonmaterialturned,tooling,andfeedsandspeedsemployed,minimumtolerancesthatcanbeheldonautomatictracerlathesarenotnecessarilythemosteconomicaltolerances.Insomecases,tolerancesof0.05mmareheldincontinuousproductionusingbutonecut.groovewidthcanbeheldto0.125mmonsomeparts.Boresandsingle-pointfinishescanbeheldto0.0125mm.Onhigh-productionrunswheremaximumoutputisdesirable,aminimumtoleranceof0.125mmiseconomicalonbothdiameterandlengthofturn.
- 内容简介:
-
-
- 温馨提示:
1: 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
人人文库网所有资源均是用户自行上传分享,仅供网友学习交流,未经上传用户书面授权,请勿作他用。