Unit-12-Material-Forming-Processes-機(jī)電專業(yè)英語(yǔ)-圖文課件

1、Unit 12 Material Forming ProcessesContentsNew Words & Expressions Text & TranslationComplex Sentence AnalysisKey to ExercisesNew Words & Expressions squeeze skwi:z v. 壓榨, 擠, 擠榨ingot igt n. (冶) 錠鐵, 工業(yè)純鐵profile prufailn. 剖面, 側(cè)面, 外形, 輪廓ceramic sirmik adj. 陶器的sinter sint v. 燒結(jié)oxidation ksideinn. 氧化New W

2、ords & Expressions solidification slidifikein n. 凝固longitudinal lnditju:dinl adj. 經(jīng)度的, 縱向的erosive irusiv adj. 侵蝕性的, 腐蝕性的dissolution dislu:n n. 分解, 解散electrolyte ilektrulait n. 電解, 電解液sodium chloride sudim kl:raid 氯化鈉New Words & Expressions sodium nitrate sudim naitreit 硝酸鈉ferrous fers adj. 鐵的, 含鐵的,

3、亞鐵的oxyacetylene ksisetili:n adj.氧乙炔的acetylene setili:n n.乙炔, 電石氣combustible kmbstbl adj. 易燃的plasma plzm n. 等離子體, 等離子區(qū)Text & TranslationIn this text，a short description of the process examples will be given. But assembly and joining processes are not described here. 1. Forging Forging can be characte

4、rized as: mass conserving, solid state of work material (metal), and mechanical primary basic process-plastic deformation. A wide variety of forging processes are used, and Fig. 12-1 (a) shows the most common of these: drop forging. The metal is heated to a suitable working temperature and placed in

5、 the lower die cavity. The upper die is then lowered so that the metal is forced to fill the cavity. Text & Translation 1Excess material is squeezed out between the die faces at the periphery as flash, which is removed in a later trimming process. When the term forging is used, it usually means hot

6、forging. Cold forging has several specialized names. The material loss in forging processes is usually quite small. Normally, forged components require some subsequent machining, since the tolerances and surfaces obtainable are not usually satisfactory for a finished product. Forging machines includ

7、e drop hammers and forging presses with mechanical or hydraulic drives. These machines involve simple translatory motions. Text & Translation2. Rolling Rolling can be characterized as: mass conserving, solid state of material, mechanical primary basic process-plastic deformation. Rolling is extensiv

8、ely used in the manufacturing of plates, sheets, structural beams, and so on. Fig. 12-1 (b) shows the rolling of plates or sheets. An ingot is produced in casting and in several stages. It is reduced in thickness, usually while hot. Since the width of the work material is kept constant, its length i

9、s increased according to the reductions. After the last hot-rolling stage, a final stage is carried out cold to improve surface quality and tolerances and to increase strength. In rolling, the profiles of the rolls are designed to produce the desired geometry as needed. Text & Translation3. Powder C

10、ompaction Powder compaction can be characterized as: mass conserving, granular state of material, mechanical basic process-flow and plastic deformation. In this text, only compaction of metal powders is mentioned, but generally compaction of molding sand, ceramic materials, and so on, also belong to

11、 this category. Text & TranslationIn the compaction of metal powders (Fig. 12-1 (c) the die cavity is filled with a measured volume of powder and compacted at pressures typically around 500 N/mm2. During this pressing phase, the particles are packed together and plastically deformed. Typical densiti

12、es after compaction are 80% of the density of the solid material. Because of the plastic deformation, the particles are “welded” together, giving sufficient strength to withstand handling. After compaction, the components are heat-treated-sintered-normally at 70%80% of the melting temperature of the

13、 material. The atmosphere for sintering must be controlled to prevent oxidation. The duration of the sintering process varies between 30 min and 2 h. the strength of the components after sintering can, depending on the material and the process parameters, closely approach the strength of the corresp

14、onding solid material. Text & TranslationThe die cavity, in the closed position, corresponds to the desired geometry. Compaction machinery includes both mechanical and hydraulic presses. The production rates vary between 6 and 100 components per minute. 4. Casting Casting can be characterized as: ma

15、ss conserving, fluid state of material, mechanical basic process-filling of the die cavity. Casting is one of oldest manufacturing methods and one of the best known processes. The material is melted and poured into a die cavity corresponding to the desired geometry ( Fig. 12-1(d). The fluid material

16、 takes the shape of the die cavity and this geometry is finally stabilized by the solidification of the material. Text & TranslationFig. 12-1 Mass-conserving Processes in the Solid State of the Work Material Text & TranslationThe stages or steps in a casting process are the making of a suitable mold

17、, the melting of the material, the filling or pouring of the material into the cavity, and the solidification. Depending on the mold material, different properties and dimensional accuracies are obtained. Equipment used in a casting process includes furnaces, mold-making machinery, and casting machi

18、nes. Text & Translation5.Turning Turning can be characterized as：mass reducing, solid state of work material, mechanical primary basic process-fracture. The turning process, which is the best known and most widely used mass-reducing process, is employed to manufacture all types of cylindrical shapes

19、 by removing material in the form of chips from the work material with a cutting tool ( Fig.12-2 (a). The work material rotates and the cutting tool is fed longitudinally. The cutting tool is much harder and more wear resistant than the work material. A variety of types of lathes are employed, some

20、of which are automatic in operation. The lathes are usually powered by electric motors which, through various gears, supply the necessary torque to the work material and provide the feed motion to the tool. Text & TranslationA wide variety of machining operations or processes based on the same metal

21、-cutting principle are available; among the most common are milling and drilling carried out on various machine tools. By varying the tool shape and the pattern of relative work-tool motions, many different shapes can be produced (Fig. 12-2 (b) and (c). Text & Translation6. EDM Electrical discharge

22、machining (EDM) can be characterized as：mass reducing, solid state of work material, thermal primary basic process-melting and evaporation (Fig. 12-2 (d). In EDM, material is removed by the erosive action of numerous small electrical discharges (sparks) between the work material and the tool (electr

23、ode), the latter having the inverse shape of the desired geometry. Text & Translation2Each discharge occurs when the potential difference between the work material and the tool is large enough to cause a breakdown in the fluid medium, fed into the gap between the tool and work piece under pressure,

24、producing a conductive spark channel. The fluid medium, which is normally mineral oil or kerosene, has several functions. It serves as a dielectric fluid and coolant, maintains a uniform resistance to the flow of current, and removes the eroded material. The sparking, which occurs at rate of thousan

25、ds of times per second, always occurs at the point where the gap between the tool and work piece is smallest and develops so much heat that a small amount of material is evaporated and dispersed into the fluid. The material surface has a characteristic appearance composed of numerous small craters.

26、Text & Translation7. ECM Electrochemical machining (ECM) can be characterized as：mass reducing, solid state of work material, chemical primary basic process-electrolytic dissolution (Fig. 12-2 (e). Electrolytic dissolution of the work piece is established through an electric circuit, where the work

27、material is made the anode, and the tool, which is approximately the inverse shape of the desired geometry, is made the cathode. The electrolytes normally used are water-based saline solutions (sodium chloride and sodium nitrate in 10%30% solutions). The voltage, which usually is in the range 5 V20

28、V, maintains high current densities, 0.5 A/mm22 A/mm2, giving a relatively high removal rate, 0.5 cm3/min1000 A6 cm3/min1000 A, depending on the work material. Text & Translation8. Flame Cutting Flame cutting can be characterized as: mass reducing, solid state of work material, chemical primary basi

29、c process-combustion (Fig. 12-2 (f). In flame cutting, the material (a ferrous metal) is heated to a temperature where combustion by the oxygen supply can start. Theoretically, the heat liberated should be sufficient to maintain the reaction once started, but because of heat losses to the atmosphere

30、 and the material, a certain amount of heat must be supplied continuously. A torch is designed to provide heat both for starting and maintaining the reaction. Most widely used is the oxyacetylene cutting torch, where heat is created by the combustion of acetylene and oxygen. The oxygen for cutting i

31、s normally supplied through a center hole in the tip of the torch. Text & TranslationFig. 12-2 Mass-reducing Processes in the Solid State of the Work Material Text & TranslationThe flame cutting process can only by used for easily combustible materials. For other materials, cutting processes based o

32、n the thermal basic process-melting have been developed (are cutting, are plasma cutting, etc.). This is the reason cutting under both thermal and chemical basic processes. Text & Translation本文將通過舉例簡(jiǎn)單描述幾種金屬的切削加工工藝，不包括裝配和連接工藝。1.鍛造 鍛造是對(duì)固態(tài)金屬材料進(jìn)行初步機(jī)械加工，是產(chǎn)生塑性成形的質(zhì)量守恒的一種基本工藝方法。鍛造有很多類型，如圖12-1(a) 所示為普通的落錘鍛造：

33、。金屬加熱到適合加工的溫度，并放進(jìn)下型腔里。上型腔與下型腔合攏，迫使金屬充滿型腔。多余的材料被從型腔接縫處擠出，并將被后續(xù)的清理型腔接縫工藝清除。當(dāng)提到鍛造術(shù)語(yǔ)時(shí)，通常意味熱鍛。冷鍛有幾種專門的名稱。鍛造工藝中損失的材料通常相當(dāng)少。Text & Translation通常，由于公差和表面粗糙度通常不能滿足最終產(chǎn)品的需要，因此對(duì)鍛造的零件要進(jìn)行一些后續(xù)加工。鍛造機(jī)械包括落錘和機(jī)械或水力驅(qū)動(dòng)的鍛壓。這些機(jī)械包括簡(jiǎn)單的平移運(yùn)動(dòng)。2.滾軋 滾軋是對(duì)固態(tài)金屬材料進(jìn)行初步機(jī)械加工，使其產(chǎn)生塑性變形的質(zhì)量守恒的一種工藝方法。滾軋廣泛應(yīng)用在板材、薄板和結(jié)構(gòu)桁條等制造中。如圖12-1(b) 所示為板材或薄板的滾

34、軋。鑄造生產(chǎn)出的鐵錠加熱后，經(jīng)過幾個(gè)階段厚度上變薄。由于工件的寬度保持不變，工件的長(zhǎng)度將隨著厚度的變薄而變長(zhǎng)。在熱軋階段之后，最終階段是進(jìn)行冷卻，以提高表面質(zhì)量、公差，并提高強(qiáng)度。滾軋工藝中，根據(jù)需要，軋輥的外形被設(shè)計(jì)生產(chǎn)成期望的幾何形狀。Text & Translation圖12-1 固態(tài)下的工件材料質(zhì)量不變工藝Text & Translation3.粉末擠壓 粉末擠壓是對(duì)粒狀材料進(jìn)行機(jī)械加工，使其產(chǎn)生塑性變形的質(zhì)量守恒的一種工藝方法。在這里僅提到了金屬粉末擠壓，但通常成型砂、陶瓷材料的擠壓等也屬于此加工工藝。金屬粉末擠壓時(shí)，型腔充滿標(biāo)稱體積粉末，如圖12-1(c)所示施加大約500 N/m

35、m2 的壓力壓緊粉末。在擠壓過程中，粉末顆粒充滿型腔并發(fā)生塑性變形。擠壓后的典型密度是固態(tài)材料密度的80%。經(jīng)過塑性變形，粉末顆?！昂附印钡揭黄?，強(qiáng)度足夠經(jīng)受得住一般操作。擠壓后，零件要以融化溫度的70%80%進(jìn)行一般燒結(jié)熱處理。燒結(jié)用的空氣一定要控制好，以防止氧化。根據(jù)材料和工藝參數(shù)，燒結(jié)過程的持續(xù)時(shí)間從30分鐘到2小時(shí)不等，燒結(jié)后零件強(qiáng)度非常接近相應(yīng)固體材料的強(qiáng)度。Text & Translation閉合的型腔形狀與期望得到的零件幾何形狀相對(duì)應(yīng)。擠壓機(jī)械包括機(jī)械壓力擠壓機(jī)和水力壓力擠壓機(jī)兩種。生產(chǎn)率為每分鐘6100個(gè)零件。4.鑄造 鑄造是將液態(tài)材料充滿型腔的質(zhì)量守恒的一種基礎(chǔ)機(jī)械工藝方法。

36、鑄造是最古老的加工方法之一，同時(shí)是最廣為人知的一種工藝。材料被融化，并灌入根據(jù)希望得到的幾何形狀制作的相應(yīng)型腔(見圖12-1(d)。液體材料充滿型腔，隨著材料凝固，零件的幾何形狀最終固定下來(lái)。Text & Translation鑄造工藝中的階段或步驟包括制作適當(dāng)?shù)蔫T型，熔化材料，將材料充滿或灌注進(jìn)型腔和凝固。根據(jù)采用的不同鑄型材料，可獲得不同特性和尺寸精度的鑄件。鑄造工藝中使用的設(shè)備包括熔爐、鑄型制作機(jī)械和鑄造機(jī)械。Text & Translation5.車削 車削是通過破裂，對(duì)固態(tài)工件進(jìn)行初步的基礎(chǔ)機(jī)械加工，質(zhì)量減少的一種工藝方法。車削工藝廣為人知，并且是使用最廣泛的質(zhì)量減少的工藝方法。車削

37、工藝中使用切削刀具，從工件上以碎片形狀切去材料(見圖12-2(a)，用于生產(chǎn)各種類型的圓柱形工件。加工時(shí)，工件旋轉(zhuǎn)，切削刀具縱向進(jìn)給。切削刀具比工件更加堅(jiān)硬和抗磨損?？刹捎貌煌愋偷能嚧玻行┻€是自動(dòng)操作的。車床通常是電動(dòng)機(jī)驅(qū)動(dòng)的，通過不同的齒輪系統(tǒng)，向工件提供必要的扭矩，使刀具進(jìn)行進(jìn)給動(dòng)作。Text & Translation利用相同金屬切削原理，也會(huì)得到完全不同的加工操作或工藝，磨和鉆就是其中最普通的一個(gè)例子，由于采用不同的加工刀具而產(chǎn)生完全不同的兩種加工操作。不同的刀具形狀和相關(guān)加工刀具運(yùn)動(dòng)模式，可生產(chǎn)出許多不同的形狀(見圖12-2(b)和12-2(c)。Text & Translati

38、on6.電火花加工 電火花加工(EDM) 是通過融化和蒸發(fā)，對(duì)固態(tài)工件進(jìn)行以熱變化為主要基礎(chǔ)，質(zhì)量減少的一種工藝方法，如圖12-2(d)所示。在電火花加工中，通過工件和工具(電極)之間許多小電火花的侵蝕動(dòng)作來(lái)去除材料，工具具有希望得到的工件幾何形狀的反轉(zhuǎn)形狀。當(dāng)工件和工具之間電壓差異足夠大時(shí)，液體介質(zhì)被擊穿，并在電壓作用下，進(jìn)入工具和工件之間的縫隙，形成傳導(dǎo)火花的通道，這時(shí)出現(xiàn)了放電。流體介質(zhì)通常是礦物油或煤油，它有幾種功能：作為絕緣的流體和散熱劑，為電流維持不變的電阻，去除侵蝕的材料。電火花以每秒成千上萬(wàn)次的速度出現(xiàn)，且總是出現(xiàn)在工具和工件間縫隙最小的點(diǎn)上，產(chǎn)生大量的熱使得少量的材料給侵蝕并

39、散入液體中。電火花加工后的材料表面具有的特點(diǎn)是它由許多小彈坑組成。Text & Translation圖12-2 固態(tài)下的工件材料質(zhì)量減少工藝Text & Translation7.電氣化學(xué)加工 電氣化學(xué)加工(ECM)是通過電解分解，對(duì)固態(tài)工件進(jìn)行以化學(xué)變化為主要基礎(chǔ)、質(zhì)量減少的一種工藝方法(見圖12.-2(e) 。工件的電解分解是通過一個(gè)電路實(shí)現(xiàn)的，工件作為陽(yáng)極，工具作為陰極。工具具有希望得到的工件幾何形狀的近似反轉(zhuǎn)形狀。電解液通常使用水基鹽(氯化鈉10% 和硝酸鈉30%)。通常使用520 V電壓，可維持高的電流密度0.5 2A/mm2，相對(duì)高的移動(dòng)速度0.56 cm3/min1000A，這

40、些都根據(jù)工件來(lái)具體確定。Text & Translation8.火焰切割 火焰切割是通過燃燒，對(duì)固態(tài)工件進(jìn)行以化學(xué)變化為主要基礎(chǔ)，質(zhì)量減少的一種工藝方法(見圖12-2) ?；鹧媲懈钪校牧?含鐵金屬)被加熱到供氧時(shí)可開始燃燒的溫度。理論上，一旦開始燃燒，釋放的熱量應(yīng)該足夠維持反應(yīng)，但由于熱量散失到空氣和材料中，因此要不斷地提供一定量的熱量。設(shè)計(jì)一個(gè)噴槍來(lái)提供開始和維持反應(yīng)所需的熱量。使用最廣泛的是乙炔切削噴槍，通過燃燒乙炔和氧氣產(chǎn)生熱量。切削用的氧氣通常通過噴槍頂端中心的孔提供?；鹧媲邢鞴に噧H適用于易燃材料。對(duì)于其他材料，可采用通過熔化、以熱變化為基礎(chǔ)的切削工藝(切削、等離子切削等)。這是以熱變化和化學(xué)變化為基礎(chǔ)的切削工藝的前提。 Complex Sentence Analysis 1 Excess material is squeezed out between the die faces at the periphery as flash, which is removed in a later trimming process. 多余的材料