Unit-10-Electrical-Discharge-Machining-機(jī)電專業(yè)英語-圖文課件

1、Unit 10 Electrical Discharge MachiningContentsNew Words & Expressions Text & TranslationComplex Sentence AnalysisKey to ExercisesNew Words & Expressions Electrical-discharge machining (EDM) 電火花加工pulsating plseiti adj. 脈沖的，脈動的DC (direct current) 直流電dielectric daiilektrik n. 電介質(zhì)，絕緣體 adj.非傳導(dǎo)性的mount mau

2、nt v.安放，設(shè)置electrode ilektrud n.電極New Words & Expressions servomotor s:vumut n.伺服電機(jī)rectifier rektifai n.整流器vibrator vaibreit n.振動器；振蕩器multi vibrator 多頻振蕩器oscillator sileit n.振動器circuit s:kit n.電路，線路vicinity visiniti n.附近，臨近evaporate ivpreit v.蒸發(fā)；消失New Words & Expressions vaporize veipraiz v.使蒸發(fā)crater

3、 kreit n.坑erode irud v.侵蝕，腐蝕，逐漸消蝕掉globule glbju:l n.小球servo-control n.伺機(jī)控制，隨動控制microsecond n.微秒；一百萬分之一秒servodrive 伺服傳動裝置；伺服控制cavity kviti n.洞，穴New Words & Expressions extrusion ekstru:n n.擠壓（成型）die dai n.模具，沖模graphite grfait n. 石墨，黑鉛cemented carbide 硬質(zhì)合金，燒結(jié)炭化物sinter sint v. 燒結(jié)high-aspect-ratio 高深寬比，

4、高縱橫比flush fl v. 沖洗fuel-injector nozzle 噴油嘴Text & TranslationElectrical discharge machining (EDM)，which is also called spark machining，removes material with repetitive spark discharges from a pulsating DC power supply，with a dielectric flowing between the workpiece and the tool.Text & TranslationThe

5、working principle of the EDM process is illustrated by the simplified diagram in Fig.101. 1The tool is mounted on the chuck attached to the machine spindle whose motion is controlled by a servo controlled feed drive. The workpiece is placed in a tank filled with a dielectric fluid；a depth of at leas

6、t 50 mm over the work surface is maintained to eliminate the risk of fire. The tool and workpiece are connected to a pulsating DC power supply. Dielectric fluid circulates under pressure by a pump，usually through a hole (or holes) in the tool electrode. The servomotor maintains a spark gap of about

7、0.025 to 0.05 mm.Text & TranslationIn power supply system of EDM，the input power is first converted into continuous DC power by conventional solid state rectifiers. The flow of this DC power is then controlled by a bank of power transistors which are switched by a digital multi vibrator oscillator c

8、ircuit. 2The high power pulsed output is then applied to the tools and workpiece to produce the sparks responsible for material removal. Text & TranslationFig. 10-1 Basic feature of electrical-discharge machiningText & TranslationEach spark generates a localized high temperature on the order of 12 0

9、00 C in its immediate vicinity. This heat causes part of the surrounding dielectric fluid to evaporate；it also melts and vaporizes the metal to form a small crater on the work surface. Since the spark always occurs between the points of the tool and work that are closest together，the high spots of t

10、he work are gradually eroded，and the form of the tool is reproduced on the work. The flowing dielectric fluid carries the condensed metal globules away，which are formed during the working process. As the metal is eroded，the tool is fed toward the workpiece by a servo controlled feed mechanism.Text &

11、 TranslationEach pulse in the EDM cycle lasts for only a few microseconds. Repeated pulses，at rates up to 100 000 per second，result in uniform erosion of material from the workpiece and from the electrode. As the process progresses，the electrode is advanced by the servo drive toward the workpiece to

12、 maintain a constant gap distance until the final cavity is produced.Text & TranslationElectrical discharge machining can be used for all electrically conducting materials regardless of their hardness. The process is quite suitable to produce the sinking of irregularly shaped holes，slots，and cavitie

13、s. Fragile workpieces can be machined without any damages. Holes can take various shapes and can be produced at shallow angles in curved surfaces，in which case workers dont have to worry about the problem of tool wander.Text & TranslationThe EDM process is widely used in tool making，especially in th

14、e manufacture of press tools，extrusion dies，forging dies，and molds. Graphite electrodes produced by copy milling from patterns are often used.A great advantage of EDM is that the tool or die can be machined after it is hardened and hence great accuracy can be achieved. 3Tools of cemented carbide can

15、 be machined after final sintering，which eliminates the need for an intermediate partial sintering stage，thus eliminating the inaccuracies resulting from final sintering after holes，slots，and so on，are machined.Text & TranslationElectrical discharge machining can be used effectively to drill small h

16、igh aspect ratio holes. Diameters as small as 0.3 mm in materials 20 mm or more in thickness can be easily achieved. With sufficient flushing，holes with aspect ratios as high as 1001 can be produced. The process has been used successfully to produce very small diameter holes in hardened fuel injecto

17、r nozzles. Varying number of holes in a precise pattern can be drilled around the injector tip.Text & Translation電火花加工（EDM）或放電加工，它是通過脈沖直流電源不斷地產(chǎn)生火花放電來去除工件材料的，工件與刀具之間有絕緣液體介質(zhì)。Text & Translation如圖10-1所示為被簡化的圖，它描述了EDM工藝的原理。工具被安裝在機(jī)床主軸的卡盤上，它的運動由伺服控制進(jìn)給驅(qū)動。工件安裝在一個盛滿液體介質(zhì)的箱中；液面至少在工作表面50 mm以上以排除燃燒的風(fēng)險。工具和工件通過直流脈沖

18、電源連接。液體介質(zhì)通常通過工具電極上的一個孔（或多個孔）在泵提供的壓力下流動。約0.0250.05 mm的火花間隙能通過伺服電機(jī)保持。Text & Translation圖10-1電火花加工的基本特征Text & Translation在EDM電源中，輸入電源首先被常規(guī)的晶體整流器轉(zhuǎn)化成連續(xù)的直流電。隨后直流電流由一組作為多頻振蕩器電路開關(guān)的功率晶體管控制。高功率脈沖輸出到工具和工件中以產(chǎn)生可靠的電火花來去除材料。Text & Translation每個電火花在它的附近產(chǎn)生規(guī)定的12 000 的局部高溫。其熱量導(dǎo)致零件周圍的液體介質(zhì)蒸發(fā)，它也融化和蒸發(fā)金屬已在零件的工作面形成小坑。由于電火花總

19、是發(fā)生在工具上的一些點與工件最接近處，工件的上高的點就被逐漸侵蝕，并且工具的外形被復(fù)制到工件上。在加工過程中形成濃縮的金屬小球由流動的電介質(zhì)流體帶走。當(dāng)金屬被完全侵蝕，工具就通過伺服控制進(jìn)給機(jī)構(gòu)向工件方向進(jìn)給。Text & TranslationEDM循環(huán)的每個脈沖維持了幾個微妙的時間。按照每秒100 000次以上的頻率重復(fù)的脈沖，使工件和電極材料侵蝕相同。隨著工藝的發(fā)展，電極能通過向工件方向的伺服驅(qū)動來保持間隙距離為常數(shù)，直到最后的孔洞被加工出來。電火花加工能用于所有導(dǎo)電材料而不管其硬度如何。該工藝最適合加工不規(guī)則形狀的孔、槽和空腔。脆性工件能被加工而不會破裂。電火花加工可加工出各種形狀的孔

20、以及曲面上角度很小的孔，且不存在工具漂移的問題。Text & Translation目前，EDM廣泛地應(yīng)用于模具制造，特別是壓力模具、擠壓模具、鍛模和鑄模等。通過對圖案復(fù)制的銑削加工得到的石墨電極被經(jīng)常采用。EDM最有利的是工具或模具能在它變硬后被加工，因此能得到極高的精度。燒結(jié)后的硬質(zhì)合金工具能被加工，它取消了部分燒結(jié)時期的介質(zhì)，因而也消除了孔、槽等諸如此類的加工誤差。Text & Translation電火花加工能高效地用于鉆小的高縱橫比的孔。20 mm厚的材料上直徑為0.3 mm的孔或更厚材料都能容易地加工完成。帶著高效沖洗，縱橫比100:1的孔也能被加工出來。電火花加工已經(jīng)成功地用于淬

21、硬噴油嘴中的極小孔的加工。噴頭周圍具有精確形狀的大量不同的孔也能被加工出來。Complex Sentence Analysis1 The tool is mounted on the chuck attached to the machine spindle whose motion is controlled by a servo-controlled feed drive. 工具被安裝在機(jī)床主軸的卡盤上，它的運動由伺服控制進(jìn)給驅(qū)動。 whose：引導(dǎo)定語從句，修飾tool attached：過去分詞做the chuck的后置定語Complex Sentence Analysis2 The

22、high-power pulsed output is then applied to the tools and workpiece to produce the sparks responsible for material removal. 高功率脈沖輸出到工具和工件中以產(chǎn)生可靠的電火花來去除材料。 (be) responsible for：為負(fù)責(zé)，是造成的原因，responsible for 做后置定語修飾sparks 此句是一個被動的語態(tài)，主語為the high-power pulsed output，pulsed做定語修飾outputComplex Sentence Analysi

23、s3 Tools of cemented carbide can be machined after final sintering, which eliminates the need for an intermediate partial sintering stage, thus eliminating the inaccuracies resulting from final sintering after holes, slots, and so on, are machined. 燒結(jié)后的硬質(zhì)合金工具能被加工，它消除了部分燒結(jié)時期的介質(zhì)，因而也消除了孔、槽等諸如此類的加工誤差。 which：引導(dǎo)定語從句，并在從句中做主語，