机械毕业设计英文外文翻译460数字控制 2.docx

机械毕业设计英文外文翻译460数字控制 2.docx

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机械毕业设计英文外文翻译460数字控制2

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科技译文：

NumericalControl

NumericalControl（NC）isamethodofcontrollingthemovementsofmachineComponentsbydirectlyinsertingcodedinstructionsintheformofnumericaldata（numbersanddata）intothesystem.Thesystemautomaticallyinterpretsthesedataandconvertstooutputsignals.Thesesignals,inturncontrolvariousmachinecomponents,suchasturningspindlesonandoff,changingtools,movingtheworkpieceorthetoolsalongspecificpaths,andturningcuttingfluitsonandoff.

Inordertoappreciatetheimporterofnumericalcontrolofmachines,let’sbrieflyreviewhowaprocesssuchasmachininghasbeencarriedouttraditionally.Afterstudyingtheworkingdrawingofapart,theoperatorsetsuptheappropriateprocessparameters（suchascuttingspeed,feed,depthofcut,cuttingfluid,andsoon）,determinesthesequenceofoperationstobeperformed,clampstheworkpieceinaworkholdingdevicesuchaschuckorcollet,andproceedstomakethepart.Dependingonpartshapeandthedimensionalaccuracyspecified,thisapproachusuallyrequiresskilledoperators.Furthermore,themachiningprocedurefollowedmaydependontheparticularoperators,andbecauseofthepossibilitiesofhumanerror,thepartsproducedbythesameoperatormaynotallbeidentical.Partqualitymaythusdependontheparticularoperatororeventhesameoperatorondifferentdaysordifferenthoursoftheday.Becauseofourincreasedconcernwithproductqualityandreducingmanufacturingcosts,suchvariabilityanditseffectsonproductqualityarenolongeracceptablethissituationcanbedliminatedbynumericalcontrolofthemathiningoperation.

Wecanillustratetheimportanceofnumericalconcrolbythefollowingexample.Asumethatholeshavetobedrilledonapartinthepositionsshowninthepicture.Inthetraditionalmanualmethodofmachiningthidpart,theoperatorpositionsthedrillwithrespecttotheworkpiece,usingaserfererencepointsanyofthethreeofthemethodshown.Theoperatorthenproceedstodrilltheseholes.Let,sassumethat100parts,havingexactlythesameshapeanddimensionalaccuracy,havetobedielled.Obviously,thisoperationisgoingtobetediiousbecausetheoperatorhastogothrouththesamemotionsagainandagain.Moreover,theprobabilutyishighthat,faorwariousreasons,someofthepathsmachinedwillbedifferentfromorthers.Let`sfurtherassumethatduringthisproductionrun,theorderforthesepathsischanged,sothat10ofthepathsnowrequireholesindifficultpositions.Themachinisstnowhastoresetthemathine,wehichwillbetimeconsumingandsubjecttoerror.Suchoperationscanbeperfomedeasilybynumericalconctrolmachinesthatarecapableofproducingpartsreeatedlyandaccuratelyandofhandlingdiffereentpartsbysimplylondingdiffereentpartprograms.

Innumericalcontrol,dataconcerningallaspectsofthemachiningoperation,suchaslocations,speeds,andcuttingfluid,arestoredonmagnetictape.,cassettes,floppyorharddisks,orpaperorplastic（Mylar,whichisathermoplasticpolyester）tape,.Datearestoredonpunched25mmwidepaperorplastictape,asoriginallydevelopedandstillused.TheconceptofNCcontrolisthatholesinthetaperepresentspecificinformationintheformofalphanumericcodes,Thepresence（on）orabsence（off）,oftheseholesisreadbysensingdevicesinthecontuolpanel,whichthenactuaterelaysandotherdevices（calledhard-wiredcontuols）,Thesedevicescontrolvariousmechanicalandelectricalsysteminthemachine.Thismethodeliminnatedmanualsettingofmachinepositionsandtoolpathsortheuseoftemplatesandothermechanicalguidesanddevices.Conplexoperations,suchasturningaparthavingvariouscontoursanddiesinkinginmillingmachine,canbecarriedout.

Numericalcontrolhashadamajorimpactonallaspectsofmanufacturingoperations.Itisawidelyappliedtechnology,particularlyinthefollowingareas:

a）Machiningcenters

b）Milling,turning,boring,drilling,andgringing

c）Electrical-discharge,laser-beam,andelectron-beammachining

d）Water-jetcutting

e）Punchingandnibbling.

f）Pipebendingandmetalspinning.

g）Soptweldingandmetalspinning.

h）Assemblyoperations.

Numericalcontrolmachinesarenowusedextensivelyinsmall-and-medium-quantity（typically500partsorless）ofawidevarietyofpartsinsmallshopsandlargemanufacturefacilities.Oldermachinescanberetrofittedwithnumericalcontrol.

AdvantagesandLimitationsNumericalcontrolhasfollowingadvantagesoverconventionalmethodofmachinecontrol:

1.Flexibilityofoperationandabilitytoproducecomplexshapewithgooddimensionalaccuracy,repeatability,reducedscraploss,andhighproductionrates,productivity,andproductquality.

2.Toolingcostsarereduced,sincetemplatesandotherfixturesarenotrequired.

3.Machineadjustmentsareeasytomakewithminicomputeranddigitalreadout.

4.Moreoperationscanbeperformedwitheachsetup,andlessleadtimeforsetupandmachiningisrequiredcomparedtoconventionalmethods.Designchangesarefacilitated,andinventoryisreduced.

5.Programscanpreparedrapidlyandcanberecalledatanytimeutilizingmicroprocessors,Lesspaperworkisinvolved.

6.Fasterprototypeproductiongispossible.

7.Requiredoperatorskillisless,andtheoperatorhasmoretimetoattendtoothertasksintheworkarea.

ThemajorlimitationsofNCaretherelativelyhighcostoftheequipmentandtheneedforprogrammingandspecialmaintenance,requiringtrainedpersonal.BecauseNCmachinesarecomplexsystems,breakdownscanbeverycostly,sopreventivemaintenanceisessential.However,theselimitationsareofteneasilyoutweighedbytheoveralleconomicadvantagesofNC.

Oneofthemostfundamentalconceptsintheareaofadvancedmanufacturingtechnologiesisnumericalcontrol（NC）

Controllingamachinetoolusingapunchedtapeorstoredprogramisknownasnumericalcontrol（NC）.NChasbeendefinedbytheElectronic

Industries.Association（EIA）as"asysteminwhichactionsarecontrolledbythedirectinsertionofnumericaldataatsomepoint.Thenumericaldataatsomepoint.Thenumericaldatarequiredtoproduceapartisknownasapartprogram.

Anumericalcontrolmachinetollsystemcontainsamachinecontrolunit（MCU）andthemachinetoolitself（Fig2.16）TheMCUisfurtherdividedintotwoelements:

Thedataprocessingunit（DPU）andthecontrolloopsunit（CLU）.TheDPUprocessesthecodedatafromthetapeorothermediaandpassesinformationonthepositionofeachaxis,requireddirectionofmotion,feedrate,andauxiliaryfunctioncontrolsignalstotheCLU.TheCLUoperatesthedrivemechanismsofeachoftheaxesandsignalsthecompletionofoperation.TheDPUsequentiallyreadsthedata.Wheneachlinehascompletedexecutionofoperation.TheDPUsequentiallyreadthedata.WheneachlinehascompletedexecutionasnotedbytheCLU,anotherlineofdataisread.

Adataprocessingunitconsistsofsomeorallofthefollowingparts:

1）Datainputdevicesuchasapapertapereader,RS232-Cport,etc

2）Data-readingcircuitsandparity-checkinglogic

3）Decodingcircuitsfordistributingdataamongthecontrolledaxes

4）Aninterpolator,whichsuppliesmachine-motioncommandsbetweendatapointsfortoolmotion

Acontrolloopsunit,ontheotherhandconsistsofthefollowing:

1）Positioncontrolloopsforalltheaxesofmotion,whereachaxishasaseparatecontrolloop

2）Velocitycontrolloops,wherefeedcontrolisrequired

3）Decelerationandbacklashtakeupcircuits

4）Auxiliaryfunctionscontrol,suchascoolanton/off,gearchanges,spindleon/offcontrol

GeometricandkinematicsdataaretypicallyfedfromtheDPUtotheCLU.

TheCLUthengovernsthephysicalsystembasedonthedataformtheDPU.Numericalcontrolwasdevelopedtoovercomethelimitationofhumanoperators,andithasdoneso.Numericalcontrolmachinesaremoreaccuratethanmanuallyoperatedmachines,theycanproducepartsmoreuniformly,theyarefaster,andthelong-runtoolingcostsarelower.ThedevelopmentofNCledtothedevelopmentofseveral

Otherinnovationsinmanufacturingtechnology;

Electicdischargemachining

Laser—cuting

Electronbeamwelding

Numericalcontrolhasalsomademachingtoolsmoreversatiletheirmanuallyoperatedpredecessors.AnNCmachinetoolcanautomaticallyproduceawidevarietyofparts,eachinvolvinganassortmentofwidelyvariedandcomplexmachiningprocesses.Numericalcontrolhasallowedmanufacturerstoundertakentheproductionofpart,eachinvolvinganassortmentofwidelyvariedandcomplexmachiningprocesses.Numericalcontrolhasallowedmanufacturestoundertakentheproductionofproductsthatwouldnothavebeenfeasiblefromaneconomicperspectiveusingmanuallycontrolledmachinetoolsandprocesses.

翻译：

数字控制

数控是一种用数字控制机床各部件运动的方法，通过直接向系统输入指令代码（数字和字母）完成的。

系统自动将这些指令代码转化成信号输出。

这些信号依次控制机床个中部件的运动，比如主轴的启动和停止，刀具的选择，岩指令路径移动刀具和工件，净控制切削液的通断等等。

为了说明数控机床的重要性，我们来简单回顾一下传统机床的加工过程。

操作作者研究零件工作图后，调整合适的加工参数（如切削速度，进给量，切削深度，切削液等），安排加工顺序，然后将工件夹紧在夹具（如卡盘或夹头）上，在开始加工。

根据所规定的工件形状和尺寸精度，这种加工通常需要熟练的操作加工。

而且，其后续加工时由各个操作者完成的。

由于存在不可避免的人为误差，即便有同一个人加工出来的零件也不可能完全相同。

因此，零件的质量就可能取决于操作者的操作水平，甚至取决于该工人在不同时期或不同时间的状态。

由于我们越来越关注加工质量和降低加工成本，所以我们不再允许存在零件偏差和产品的质量影响，而通过数控加工就可以消除以上这些情况。

我们可以通过以下的例子来说明数控加工的重要性。

假如要在图示位置的零件上钻这几个孔，当传统的手工操作机床加工此零件时，操作者可选图示三种方案中的任一种，使钻头与工件的点相对应着，然后钻这些孔。

假如要加工100个同样形状，同样尺寸，同样精度的零件，很明显，操作者会觉得很枯燥，因为操作者要一遍一遍重复同样的动作，而且，由于各种原因，有些零件加工出来的不一样的可能性是很高的。

我们进一步假设，在操作过程中，零件的加工要求要改变，现在要在不同的位置加工出10个孔，机械师必须马上调整机床，这样既浪费时间又增加了加工误差。

而数控机床能够重复而准确地加工工件，而且可通过简单地输入不同程序来加工不同的零件。

因此，使用数控机床就可以轻而易举地完成此类加工。

在数控系统中，与加工过程各项相关的数据如工件的定位，切削速度，进给量和切削液，存储在磁盘，盒式录音带，软盘，硬盘，纸袋或塑料袋（热塑性树脂）上。

将数据存储在25mm宽的穿孔纸带或塑料带上，这种数据存储方法使用最早并沿用至今。

数控的概念就是纸带上的孔表示以字母代码表达的特定信息。

这些孔的打开和关闭由控制面板的感应控制，然后驱动继电器和其他机械导向装置。