机械专业英语董建国

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READINGMATERIALUnit20TEXTTheEDMProcessItisknowntoeverymachinistthatelectricalenergyisconvertedintomotionbyanelectricmotoronstandardmachinetools.Recently,wehavediscoveredthatelectricalenergycanbedirectlyemployedinmetalremoval.Themainadvantageisthatmetalofanyhardnesscanbemachinedbyelectricalmachiningprocesseswithgoodsurfacefinish.

Electricaldischargemachiningisaformofmetalremovalinwhichpulsatingdirectcurrentisappliedtoashapedtool(electrode)andawork-piece,bothofwhicharecapableofconductingelectricity.Thetwoareheldclosetoeachotherwithanonconductingfluidservingasaninsulatorbetweenthem.Whenavoltagehighenoughtobreakdowntheinsulatorisreached,asparkjumpsthegapbetweenthetoolandthework-piece.Asaresult,thissparkremovesasmallportionofmaterial.ThesurfacefinishofapartproducedonanEDMmachinedependsonthesizeofthesparksgeneratedbetweenitandtheelectrode.Big,powerfulsparksproducearoughsurfaceandsmall,lesspowerfulsparksproduceasmoothsurface.Itisreportedthatmetalremovalratesandsurfacefinisharecontrolledbythefrequencyandintensityofthespark.Highfrequency,low-intensitysparksresultinalowmetalremovalrateandproduceasmoothfinish.Lowfrequency,high-intensitysparksresultinrapidmetalerosionandacoarsefinish.LEARNTOSPEAKMr.Zhang：Hello,Mr.Cheng.Mr.Cheng：Hi,Mr.Zhang.Mr.Zhang：Whatareyoudoing?Mr.Cheng：Iammachiningawork-piece.Mr.Zhang：Butthereisaflameonthework-piece.Isthisakindofmethodofwelding?Mr.Cheng：ItisEDMprocess.Mr.Zhang：WhatdoestheEDMmean?Mr.Cheng：Itmeanselectricaldischargemachining,anditusestheelectricalenergyremovedirectlythemetalofwork-piece.Mr.Zhang：Howdoesitwork?Mr.Cheng：Whenmachiningpulsatingdirectcurrentisappliedtoashapedtool(electrode)andawork-piece,bothofwhicharecapableofconductingelectricity.Whenthetwoareclosetoeachother,apowerfulsparkswillremoveasmallportionofmaterial.Mr.Zhang：Whatisitsadvantage?Mr.Cheng：Themainadvantageisthatitcanmachinemetalofanyhardnessandformagoodsurfacefinish.Mr.Zhang：Oh,howniceitis.Thanksalot.Mr.Cheng：Notatall.NEWWORDSANDEXPRESSIONSelectrical [I5lektrIk(E)l]adj.电的，电力的electrically [IlektrIkElI]adv.用电，电学上discharge [5dIstFB:dV]vt.放电discover [dI5skQvE(r)]v.发现pulsate [pQl5seIt;(?@)5pQlseIt] vi.脉动，波动current [5kQrEnt] n.电流electrode [I5lektrEJd] n.电极close [klEJs] v.关闭closely [5klEJzlI] adv.接近地，紧密地nonconducting[nBnkEndQktIN] adj.不导电的fluid [5flu:Id] n.流体，液体insulator [5InsjJleItE(r)] n.绝缘体voltage [5vEJltIdV] n.电压reach [ri:tF] vt.到达，达到spark [spB:k] n.火花，电火花jump [dVQmp] n.&v.跳gap [^Ap] n.间隙result [rI5zQlt] n.&v.结果portion [5pC:F(E)n] n.部分powerful [5paJEfJl] adj.强有力report [rI5pC:t] v.&n.报告，通报frequency [5fri:kwEnsI] n.频率，频繁erosion [I5rEJV(E)n] n.腐蚀，侵蚀electricaldischargemachining(EDM) 电火花加工directcurrent=D.C. 直流电breakdown 破坏，毁坏，击穿closetoeachother 相互靠近asaresult 结果，因此asresultof ……结果，由于resultfrom 起因，由来resultin 导致，结果形成asmallportionof 小部分NOTES1．Itisknowntoeverymachinistthat…

每一个机械师都知道……

Itis…that…句型中，it是形式主语，that…引出的从句是本句真正的主语。2．…thatmetalofanyhardnesscanbemachinedbyelectricalmachiningprocesseswithgoodsurfacefinish.

用电加工法能够加工任何硬度的金属，而且表面粗糙度小。

That引出的是表语从句，withgoodsurfacefinish是从句的状语。3．Electricaldischargemachiningisaformofmetalremovalinwhichpulsatingdirectcurrentisappliedtoashapedtool(electrode)andawork-piece,bothofwhicharecapableofconductingelectricity.

电火花加工是一种去除金属的方式。在此过程中，脉冲直流电通到能导电的成形刀具(电极)和工件上。其中inwhichpulsatingdirectcurrentisappliedtoashapedtool(electrode)andawork-piece,bothofwhicharecapableofconductingelectricity是主句的定语从句，修饰表语aformofmetalremoval，而bothofwhicharecapableofconductingelectricity则是该从句中的从句，修饰ashapedtool(electrode)andawork-piece。EXERCISES1．DiscussthefollowingquestionsinEnglish:(1) Whatistheelectricaldischargemachining(EDM)?(2) WhichworkcantheEDMdo?Givesomeexamples.(3) CantheEDMmachinetheplasticwork-piece?Why?2．UseEnglishreplacingChineseoruseChinesereplacingEnglish:(1)用电火花加工的方法可以加工很硬的金属工件。(2)电火花加工所用的刀具就是电极。(3)电火花加工可以得到高质量的表面。(4) TheEDMusedirectcurrenttomachinework-piece.(5) Thework-pieceandelectrodeareheldclosetoeachotherwithanon-conductingfluidservingasaninsulatorbetweenthem.3．Placea“T”aftersentencesthataretrueandan“F”afterthosethatarefalse:(1) Onstandardmachinetools,electricalenergyisdirectlyemployedinmetalremoval.()(2) Metalofanyhardnesscanbemachinedbyelectricalmachiningprocesseswithcoarsesurfacefinish.()(3) ThesurfacefinishofapartproducedonanEDMmachinedependsonthesizeofpart.()(4) Big,powerfulsparksproduceasmoothsurfaceandsmall,lesspowerfulsparksproducearoughsurface.()(5) Metalmaterialremovalratesandsurfacefinishcanbecontrolledbythefrequencyandintensityofthespark.()(6) Highfrequency,low-intensitysparksresultinalowmetalremovalrateandproduceasmoothsurfacefinish.()READINGMATERIALElectricalMachiningMostelectricalmachiningprocesseshavecomeaboutduetothedevelopmentofspace-agemetalalloysthataretoughandhardtomachine.Grindingcutting,andshapingwithcuttingtoolsareexacting,time-consuming,andexpensiveprocessesonsuchalloys.Insomecases,machiningwithconventionalequipmentisalmostimpossible.Amaterialliketungstencarbide,forexample,isverydifficulttomachineevenwithdiamondcuttingtools.

Onstandardmachinetools,electricalenergyisconvertedbyanelectricmotorintomotionthatistransmittedthroughaseriesofshafts,pulleys,belts,andgearstoacuttingtool.Incontrast,theelectricalmachiningprocessesmakedirectuseofelectricalenergy.Thisresultsincertainabilitiesthatareuniquetotheseprocesses.Theseincludemachiningmetalsofanyhardness,machiningwithoutcuttingforces,machiningwithouttoolrotationorwit