Unit-10-Electrical-Discharge-Machining-机电专业英语-图文课件

1、Unit 10 Electrical Discharge MachiningContentsNew Words & Expressions Text & TranslationComplex Sentence AnalysisKey to ExercisesNew Words & Expressions Electrical-discharge machining (EDM) 电火花加工pulsating plseiti adj. 脉冲的，脉动的DC (direct current) 直流电dielectric daiilektrik n. 电介质，绝缘体 adj.非传导性的mount mau

2、nt v.安放，设置electrode ilektrud n.电极New Words & Expressions servomotor s:vumut n.伺服电机rectifier rektifai n.整流器vibrator vaibreit n.振动器；振荡器multi vibrator 多频振荡器oscillator sileit n.振动器circuit s:kit n.电路，线路vicinity visiniti n.附近，临近evaporate ivpreit v.蒸发；消失New Words & Expressions vaporize veipraiz v.使蒸发crater

3、 kreit n.坑erode irud v.侵蚀，腐蚀，逐渐消蚀掉globule glbju:l n.小球servo-control n.伺机控制，随动控制microsecond n.微秒；一百万分之一秒servodrive 伺服传动装置；伺服控制cavity kviti n.洞，穴New Words & Expressions extrusion ekstru:n n.挤压（成型）die dai n.模具，冲模graphite grfait n. 石墨，黑铅cemented carbide 硬质合金，烧结炭化物sinter sint v. 烧结high-aspect-ratio 高深宽比，

4、高纵横比flush fl v. 冲洗fuel-injector nozzle 喷油嘴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电火花加工（EDM）或放电加工，它是通过脉冲直流电源不断地产生火花放电来去除工件材料的，工件与刀具之间有绝缘液体介质。Text & Translation如图10-1所示为被简化的图，它描述了EDM工艺的原理。工具被安装在机床主轴的卡盘上，它的运动由伺服控制进给驱动。工件安装在一个盛满液体介质的箱中；液面至少在工作表面50 mm以上以排除燃烧的风险。工具和工件通过直流脉冲

18、电源连接。液体介质通常通过工具电极上的一个孔（或多个孔）在泵提供的压力下流动。约0.0250.05 mm的火花间隙能通过伺服电机保持。Text & Translation图10-1电火花加工的基本特征Text & Translation在EDM电源中，输入电源首先被常规的晶体整流器转化成连续的直流电。随后直流电流由一组作为多频振荡器电路开关的功率晶体管控制。高功率脉冲输出到工具和工件中以产生可靠的电火花来去除材料。Text & Translation每个电火花在它的附近产生规定的12 000 的局部高温。其热量导致零件周围的液体介质蒸发，它也融化和蒸发金属已在零件的工作面形成小坑。由于电火花总

19、是发生在工具上的一些点与工件最接近处，工件的上高的点就被逐渐侵蚀，并且工具的外形被复制到工件上。在加工过程中形成浓缩的金属小球由流动的电介质流体带走。当金属被完全侵蚀，工具就通过伺服控制进给机构向工件方向进给。Text & TranslationEDM循环的每个脉冲维持了几个微妙的时间。按照每秒100 000次以上的频率重复的脉冲，使工件和电极材料侵蚀相同。随着工艺的发展，电极能通过向工件方向的伺服驱动来保持间隙距离为常数，直到最后的孔洞被加工出来。电火花加工能用于所有导电材料而不管其硬度如何。该工艺最适合加工不规则形状的孔、槽和空腔。脆性工件能被加工而不会破裂。电火花加工可加工出各种形状的孔

20、以及曲面上角度很小的孔，且不存在工具漂移的问题。Text & Translation目前，EDM广泛地应用于模具制造，特别是压力模具、挤压模具、锻模和铸模等。通过对图案复制的铣削加工得到的石墨电极被经常采用。EDM最有利的是工具或模具能在它变硬后被加工，因此能得到极高的精度。烧结后的硬质合金工具能被加工，它取消了部分烧结时期的介质，因而也消除了孔、槽等诸如此类的加工误差。Text & Translation电火花加工能高效地用于钻小的高纵横比的孔。20 mm厚的材料上直径为0.3 mm的孔或更厚材料都能容易地加工完成。带着高效冲洗，纵横比100:1的孔也能被加工出来。电火花加工已经成功地用于淬

21、硬喷油嘴中的极小孔的加工。喷头周围具有精确形状的大量不同的孔也能被加工出来。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. 工具被安装在机床主轴的卡盘上，它的运动由伺服控制进给驱动。 whose：引导定语从句，修饰tool attached：过去分词做the chuck的后置定语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. 高功率脉冲输出到工具和工件中以产生可靠的电火花来去除材料。 (be) responsible for：为负责，是造成的原因，responsible for 做后置定语修饰sparks 此句是一个被动的语态，主语为the high-power pulsed output，pulsed做定语修饰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. 烧结后的硬质合金工具能被加工，它消除了部分烧结时期的介质，因而也消除了孔、槽等诸如此类的加工误差。 which：引导定语从句，并在从句中做主语，