鍛造、鑄造、焊接外文翻譯

1、<p><b>　　中文4200字</b></p><p>　　畢業(yè)設(shè)計(論文)外文翻譯</p><p>　　學(xué)生姓名： </p><p>　　系 別： 機 械 工 程 系</p><p>　　專 業(yè)： 機械設(shè)計制造及其自動化</p><p>

2、　　班 級： </p><p>　　學(xué) 號: </p><p>　　譯文出處：Science and Technology Engl-</p><p>　　ish for Mechanical Engineering</p><p>　　Casting、Forging and Welding</p&g

3、t;<p>　　1. Casting</p><p>　　Metal casting is one of the oldest of all industries, both ancient and medieval history offering examples of the manufacture and use of casting. From simple axeheads poured

4、 from copper in open moulds some 5000 years age, casting in the pre-Christian world developed to a point at which elaborate bronze statuary could be produced in two-piece and cored moulds. By the end of the medieval peri

5、od, decorated bronze and pewter casting had begun to be used in European church and domestic life. </p><p>　　The widespread adoption of cast iron as engineering material awaited the success of Abraham Darby

6、in 1790 in smelting in the coke blast furnace; this paved the way for the massive use of cast iron in construction during the years following the industrial revolution.</p><p>　　Many foundries sprang up afte

7、r the industrial revolution, the vast majority being for the manufacture of the cast iron then being used as a structural material. The quantity production of iron castings in the nineteenth century was not matched by a

8、universal advance in quality and the engineering use of the products encountered more serious risks in a non-ductile material.</p><p>　　Despite the skill of the molder in producing complex forms, there was l

9、ittle change in the metallurgical and engineering situation until the modern era brought a better understanding of the factors determining quality. With modern techniques of process control the rudimentary judgment of th

10、e operator could give way to objective measurements of metal temperature, molding material properties and other production variables. These improvements have been applied not only to cast iron but to a wide ra</p>

11、<p>　　There are four basic casting methods: sand-casting, die-casting, investment-casting, and centrifugal casting.</p><p>　　Sand-casting is the most widely used method employed in foundry. In this pro

12、cess, sand moulds are contained in metal molding boxes that have four sides but no top or bottom. During the molding operation the boxes are located together by pins so that they can be separated to remove the pattern, a

13、nd replaced in the correct position before the metal is poured in. The boxes are clamped together, or the cope (top section) weighted down when pouring to prevent the cope from “floating away” from the dr</p><

14、p>　　At the first stage the pattern is seated on the moulding board. The pattern is covered with facing sand, which is a specially prepared sand of good quality, which can take a clean and smooth impression, and can re

15、sist the heat from the molten metal that will be in contact with it. The facing sand is backed up with molding sand, which is old facing sand from previous moulds. The molding sand is carefully rammed up so that it is fa

16、irly tight around the pattern to produce a good solid mould, yet pe</p><p>　　At the second stage the mould with the pattern still in position is inverted; the exposed sand lightly covered with parting sand,

17、and the exposed pattern with facing sand.(The parting sand has no cohesion, and is introduced to permit a clean separation when the mould is opened up to remove the pattern .) The second molding box is located in positio

18、n on the first box and filled with molding sand. Two or more plugs are introduced when the second box is being filled (these are removed later, leavin</p><p>　　Now, at stage 3, to allow the pattern to be rem

19、oved. This is done by screwing a bar with a threaded end into a suitable insert in the pattern, damping the sand around the pattern, and gently rapping the bar in all directions so that the pattern can be carefully withd

20、rawn. To facilitate the removal of the pattern without scuffing the sides of the impression, all surfaces that lie in the direction of pattern removal are inclined slightly by a small amount (the draw angle).</p>

21、<p>　　A groove called a gate is cut in the sand face to allow the channel produced by the plug that is outside the pattern to connect with the impression .The metal is poured through this channel (called the runner)

22、, and the gate prevents it from dropping straight into the impression and damaging it .The cross-section of the gate is slightly smaller than that of channel so that a full runner will always supply metal to the gate at

23、a slight pressure.</p><p>　　Finally, the mould is reassembled, carefully locating and securing the two sections. The top section is known as the cope, and the lower section is known as the drag. The sand in

24、the cope is vented. These vents allow the sand to be rammed up more tightly at the earlier stages without the risk of gases being trapped in the molten metal and forming blowholes in the solid metal. A sand-feeding gate

25、(also called a pouring or bowl) is added to make it easier to pour the metal into the runner. The mol</p><p>　　The impression will be filled with molten metal when it is completely filled. Gases can escape t

26、hrough the runner and the riser, which also act as headers to supply the impression with more metal to compensate for the contraction of the metal when cooling in the molten state. </p><p>　　2. Forging</

27、p><p>　　Forging is the plastic working of metal by means of localized compressive forces exerted by manual or power hammers, presses, or special forging machines. It may be done either hot or cold. however, whe

28、n it is done cold, special names usually are given to the processes. Consequently, the terms“forging” usually implies hot forging done above the recrystallization temperature.</p><p>　　Modern forging is a de

29、velopment form the ancient art practiced by the armor makers and the immortalized village blacksmith. High-powered hammers and mechanical presses have replaced the strong arm, the hammer, and the anvil and modern metallu

30、rgical knowledge supplements the art skill of the craftsman in controlling the heating and handling of the metal.</p><p>　　Forge ability is the term used in the industry to denote a material relative resista

31、nce to deformation and its plasticity. While considerable disagreement exists as to precisely what characteristics the word “forge ability” should include, the term as used here is defined as the tolerance of a metal or

32、alloy for deformation without failure, regardless of forging pressure requirements.</p><p>　　Raw material used for forging is generally bar or billet stock hot rolled from ingots melted in open-hearth, elect

33、ric arc, or vacuum arc furnace .other forms and shapes such as rolled slabs, plats, and stock produced by continuous casting techniques are occasionally used .for certain grades ,vacuum arc melting imparts better forge a

34、bility than does conventional arc melting . However, the major purpose of vacuum melting is the improvement of mechanical properties and cleanliness, not forging beha</p><p>　　Equipment behavior influences t

35、he forging progress since it determines the feasibility of forging a part and affects the rate of deformation and the temperature conditions.</p><p>　　The hammer is the most economical type of equipment for

36、generating load and energy necessary to carry out a forging process, provided that the material being forged can support high deformation velocities. It is most commonly used hot forging equipment for repeated blows on t

37、he same workpiece and cannot be overloaded.</p><p>　　There are various types of hammers: air-lift gravity drop hammers, power drop hammers, power drop hammers, Counterblow hammers ect. In a simple gravity dr

38、op hammer the upper ram is positively connected to a board, a belt, a chain or a piston. When forging the ram is lifted to a certain height and then dropped on the stock placed on the anvil. During the down stroke, the r

39、ain is accelerated by gravity and builds up the blow energy. The upstroke takes place immediately after the blow, the force ne</p><p>　　Press forging employs a slow squeezing action in deforming the plastic

40、metal, as contrasted with the rapid-impact blows of a hammer. Hydraulic forging press is operated by large pistons driven by high-pressure hydraulic or hydrometric system. The squeezing action is carried completely to th

41、e center of the part being pressed, thoroughly working the entire section. These presses are the vertical type and may be either mechanically or hydraulically operated. The mechanical presses, which are faster</p>

42、<p>　　In the forging press a grater proportion of the total work put into the machine is transmitted to the metal than in a drop hammer. The machine and foundation absorb much of the impact of the drop hammer .pres

43、s reduction of the metal is faster, and the cost of operation is consequently lower. most press forging s are symmetrical in shape ,having surfaces, which are quite smooth, and provide a closer tolerance than is obtaine

44、d by a drop hammer .however ,drop forging can forge many parts of irregu</p><p>　　For small forgings closed impression dies are used, and only one stroke of the ram is normally require to perform the forging

45、 operation .the maximum pressure is built up at the end of the stroke ,which forces the metal into shape .dies may be mounted as separate units, or all the cavities may be put into a single block. for small forgings ind

46、ividuals die units are more convenient .large ingots are now almost always forged with hydraulic presses instead of with steam hammers, since the work done</p><p>　　The forging should be done at about the sa

47、me temperature as rolling; the process improves the physical properties of the steel just as rolling does. In the final forging it is important not to have the steel too hot, for overheated steel will have poor mechanica

48、l properties when cooled. in heating for forging the temperature is usually judged by the eye, but where a large number of the same patterns will be made, the pieces to be forged are heated in furnaces in which the tempe

49、rature is indicate</p><p>　　3. welding</p><p>　　Welding techniques have become so versatile that it is difficult nowadays to define “welding”. Formerly welding was “the joining of metals by fusi

50、on”, that is, by melting, but this definition will no longer do. Welding was next defined as the “joining of metals by heat”, but this is not a proper definition either. Not only metals can be welded, so can many of the

51、plastics. Furthermore several welding methods do not require heat. Every machinist is familiar with heatless welding method under some</p><p>　　There is also no uniform method of naming welding processes. So

52、me processes are named according to the heat source or shielding method, other certain specialized processes are named after the type of joint produced. Examples are spot and butt welding. But an overall classification c

53、an not take account of this because the same type of joint may be produced by a variety of processes. Spot welding may be done by electric resistance, arc, or electron-beam processes and butt welding by resistance, fl<

54、;/p><p>　　Soldering is the process of joining two metals by a third metal to be applied in the molten state. Solder consists of tin and lead, while bismuth and cadmium are often included to lower the melting po

55、int. One of the important operations in soldering is that of cleaning the surface to be joined, this may be done by some acid cleaner. Soldering gives a satisfactory joint for light articles of steel, copper or brass, bu

56、t the strength of soldering joint is rather less than a joint which is brazed, r</p><p>　　Pressure welding is known as the simplest method of welding two pieces of metal together. The ends of metal are heate

57、d to a while heat—for iron, the welding temperature should be about 1300℃—in a flame. At this temperature the metal becomes plastics. The ends are then presses or hammered together, and the joint is smoothed off. Care mu

58、st be taken to ensure that the surfaces are thoroughly clean first, for dirt will weaken the weld. Moreover, the heating of iron or steel to a high temperature cau</p><p>　　Gas welding includes all the proce

59、sses in which gases are used to obtain a hot flame. Those commonly used are acetylene, natural gas, and hydrogen in combination with oxygen. The maximum temperature developed by oxyhydrogen welding is 3600℉ (1980℃). Hydr

60、ogen is produced either by the electrolysis of water or by passing steam over coke. An oxyacetylene weld is produced by heating with a flame obtained from the combustion of oxygen and with or without the use of a filler

61、metal. In most cases the j</p><p>　　Are welding is a process in which coalescence is obtained by heat produced from an electric arc. The electrode or filler metal is heated to a liquid state and deposited in

62、to the joint to make the weld. Contact is first made between the electrode and the work to create an electric circuit, and then, by separating the conductors, an arc is formed. The electric energy is converted into inten

63、se heat in the arc, which attains a temperature around 10 000°F (5500℃). Either direct or alternating current</p><p>　　Laser Welding is used because of laser’s high heat intensity. It can be operated in

64、 any transparent medium without contact with the workpiece, since the laser delivers its energy in the form of light. In welding, the power is delivered in pulses rather than as a continuous beam, the beam is focused on

65、the workpiece and the intense heat produces a fusion weld. Laser welding is slow and is used only for special jobs involving small weldments. Its greatest use is found in the electronics industry.</p><p>　　E

66、xplosion welding is a process that uses energy from the detonation of an explosive to join two pieces of metal. The explosion accelerates the pieces to a speed at which a metallic bond will form between them when they co

67、llide. The weld is produced in a fraction of a second without the addition of filler metal. This is essentially a room temperature process in that gross heating of the workpieces does not occur. The faying surfaces, howe

68、ver, are heated to some extent by the energy of the collisi</p><p><b>　　譯文：</b></p><p><b>　　鑄造、鍛造和焊接</b></p><p><b>　　1.鑄造</b></p><p>

69、;　　金屬鑄造是最古老的產(chǎn)業(yè)之一，遠(yuǎn)古時期和中世紀(jì)就有人使用和制造鑄件了。5000年前人們只能用銅在開式模具中澆注簡單的斧頭，而公元前已經(jīng)能夠用分體式模具和型芯制造復(fù)雜的青銅雕塑了。中世紀(jì)末期，歐洲的教堂和家庭開使使用青銅和錫鉛合金鑄件制造器皿、進行裝飾。</p><p>　　工程材料廣泛使用鑄鐵得益于1709年希伯來用鼓風(fēng)煉焦?fàn)t熔化金屬，這為工業(yè)革命時期在建設(shè)中大量使用鑄鐵鋪平了道路。</p>&

70、lt;p>　　工業(yè)革命以后鑄鐵作坊紛紛興起，生產(chǎn)的鑄件主要用作建筑材料。19世紀(jì)鑄件的產(chǎn)量雖然很大，但質(zhì)量的提高并不普遍，工程中使用這些延展性很差的材料要冒極大的風(fēng)險。</p><p>　　盡管鑄件工人已經(jīng)可以制造比較復(fù)雜的模型，但整個行業(yè)的情況幾乎沒有什么變化，直到現(xiàn)代人們才逐漸了解那些影響鑄件質(zhì)量的各種因素。現(xiàn)代加工技術(shù)不再使用那些粗略的判斷，而是對金屬溫度、材料特性以及生產(chǎn)過程中的其它因素進行客觀的測

71、量。這些改進不僅應(yīng)用到鑄鐵，而且應(yīng)用于各種澆注合金。</p><p>　　鑄造方法基本有四種：砂型鑄造、金屬模鑄造、熔模鑄造和離心鑄造。</p><p>　　砂型鑄造是鑄造廠最普遍使用的方法。鑄造時，砂模裝在沒有上、下底的金屬砂箱里。制模時砂箱用銷子連在一起，這樣取模時可以把砂箱拆開，并在澆注前作必要的校正。砂箱被夾在一起，為了防止?jié)沧⒌慕饘僭诔錆M砂箱時把上砂箱和下砂箱頂開，有時也把上砂箱

72、放在底部。分離式簡單模具的制模過程可以用托架的鑄造說明如下。</p><p>　　第一步先把托架模型放在模板上，模型上覆蓋面砂。面砂經(jīng)過專門制造，質(zhì)量很高，能夠生成干凈光滑的模腔印痕表面，抵抗熔融金屬接觸時的高溫。面砂外面用型砂填充，型砂包括用過的面砂，經(jīng)過仔細(xì)壓緊，形成堅固的模腔，并具有良好的透氣性，排放鑄造時產(chǎn)生的氣體。最后經(jīng)過整型，平整砂模表面。</p><p>　　第二步把砂箱連同

73、內(nèi)部的模型就地倒置安放，在暴露的型砂上輕輕地覆蓋一層分型砂，暴露的模型外覆蓋面砂。（分型砂內(nèi)沒有粘結(jié)劑，這樣在開箱取出模型時達(dá)到完全、清晰的分離。）第二個砂箱放在剛才第一個砂箱的上面，填滿型砂。第二個砂箱填充時要插入兩個或更多的塞子，以便塞子拔出時在砂子中間留下通孔。其中的一個塞子放置在模型的一側(cè)。最后把砂子夯實、平整。</p><p>　　第三步是取模。把一根端部刻有螺紋的起模棒旋擰進模型，把模型周圍的砂子弄濕

74、，然后輕輕在各個方向晃動起模棒并仔細(xì)地取出模型。為了便于取模而不劃傷模腔四周的印痕，沿取模方向的表面都應(yīng)該稍傾斜一個角度（拔模斜度）。</p><p>　　型砂中間要開一個溝槽，叫做內(nèi)澆口或橫澆口。內(nèi)澆口可以使前面塞子拔出時形成的不與模型相連的通孔與模腔相連。當(dāng)向這個稱為澆口的通孔內(nèi)澆注金屬時，內(nèi)澆口可以避免金屬直接沖入模腔而把表面的印痕沖壞。內(nèi)澆口的橫截面積要稍微小于澆口，這樣金屬經(jīng)過內(nèi)澆口時能保持一定的壓力。

75、</p><p>　　最后把砂箱重新裝在一起，仔細(xì)定位和固定。上面的叫做上砂箱，下面的叫做下砂箱。上砂箱的砂子中有一些小孔。這些小孔使砂子盡早被夯實，避免氣體混入熔融的金屬，在凝固的鑄件內(nèi)形成氣孔。澆口上面可以安放砂子做成的漏斗（澆口盆），方便澆注金屬。熔融的金屬從澆口澆注，氣體從冒口排除。</p><p>　　模腔注滿后內(nèi)部將完全充滿熔融的金屬。從冒口和澆口排出的氣體和內(nèi)澆口一樣可以使更

76、多的金屬注入模腔，補償金屬在熔融狀態(tài)時的收縮。</p><p><b>　　2.鍛造</b></p><p>　　鍛造是借助人工、蒸汽錘、壓力機或?qū)ｉT的鍛壓機械施加局部壓力進行金屬塑性加工的過程，它既可以是熱鍛也可以是冷鍛。由于冷鍛工藝有其它的專門的名稱，因此，“鍛造”術(shù)語指的是在結(jié)晶溫度以上進行的熱鍛。</p><p>　　現(xiàn)代鍛造工藝由盔甲

77、制造者和不朽的鄉(xiāng)村鐵匠所從事的古老技術(shù)發(fā)展而來。只不過高壓鍛錘和壓力機代替了強有力的手臂、鐵錘和砧座，現(xiàn)代冶煉知識充實了技工控制加熱和處理金屬的技術(shù)水平。</p><p>　　各種材料對使之變形的作用力的反應(yīng)差別很大。鍛造者最重要的是應(yīng)該了解如何容易地使金屬或合金在鍛造時變形而不產(chǎn)生副作用，因為鍛造材料的特性將影響鍛造方法的選擇、鍛造設(shè)備的選擇以及模具的設(shè)計。購買鍛件時應(yīng)該認(rèn)識到材料不同其可鍛性也不同，進而影響鍛

78、造工藝的設(shè)計和加工的成本。</p><p>　　可鍛性是工業(yè)上描述材料抵抗變形的相對阻力及其塑性的術(shù)語?？慑懶詰?yīng)該精確地包括哪些特性概念，仍然存在相當(dāng)?shù)臓幾h。本文的可鍛性定義為金屬或合金在不論什么樣的端正壓力下達(dá)到失效前的變形程度。</p><p>　　用于鍛造的原材料一般是由平爐、電弧爐或真空電弧爐熔煉的鋼錠熱軋而生成的棒狀或條狀鋼坯，偶爾也使用連續(xù)鑄造技術(shù)生產(chǎn)的軋板和軋塊等其它形狀的材

79、料。對于某些品牌的鋼材，真空電弧爐熔煉比傳統(tǒng)的電弧熔煉能產(chǎn)生更好的可鍛性。然而，真空熔煉的主要目的是改善機械性能，清潔生產(chǎn)環(huán)境，而不是提高材料的可鍛性。 </p><p>　　設(shè)備性能影響鍛造的發(fā)展，決定鍛件的應(yīng)用并影響變形的速度和溫度條件。 </p><p>　　如果鍛造材料能承受很高的變形速度，鍛錘就是生成鍛造工藝所必需的載荷和能量的最經(jīng)濟的設(shè)備。鍛造是常用的熱鍛設(shè)備，常用于重復(fù)錘擊

80、同一工件而不過載。 </p><p>　　有各種類型的鍛錘：重力空氣錘、蒸汽錘和對擊錘等。簡單重力空氣錘的撞錘固定連接在橫梁、皮帶、鏈條或柱塞上。鍛造時撞錘升起一定的高度，然后下落鍛打放在鐵砧上的鍛件。下落錘擊時，撞錘因重力加速獲得鍛擊能量。鍛打后撞錘立即升起，確保迅速提升撞錘所需的力是撞錘重量的三到五倍。蒸汽錘的工作原理與空氣錘類似。下落錘擊時除了重量外，撞錘還受到蒸汽、空氣或加熱氣體壓力的作用而加速。對于

81、電液重力氣錘，鍛錘依靠油壓壓縮氣體而上升。壓縮氣體減緩撞錘的上升并提供下落錘擊時所需的加速度。因此電液重力氣錘也有一定的動力鍛擊作用。</p><p>　　與錘鍛的快速沖擊不同，壓力機鍛造用緩慢的擠壓作用使金屬塑性變形。液壓壓力機由高壓液壓系統(tǒng)或液壓重力系統(tǒng)驅(qū)動的大型柱塞控制操作。擠壓作用完全施加到正在被壓鍛的零件的中心，徹底加工整個橫截面。這些壓力機都是立式的，可以采用機械操作也可以采用液壓操作。機械壓力機的鍛

82、造能力范圍在5000噸到10000噸，操作速度比較快而且使用普遍。</p><p>　　壓力機輸入到機器里的總能量比落錘鍛的總能量傳輸?shù)浇饘偕系母?，因為機器和基礎(chǔ)吸收了落錘段更多的沖擊。金屬的壓力變形較快，因此生產(chǎn)成本較低。大多數(shù)壓力機鍛造的形狀是對稱的，表面非常光，公差尺寸比落錘鍛件的更精確。然而落錘鍛鍛制形狀復(fù)雜而不規(guī)則的鍛件比較經(jīng)濟。壓力機常常用來對其它鍛造工藝所產(chǎn)生的鍛件進行整形加工。</p>

83、;<p>　　小型鍛件使用閉式模鍛，鍛錘通常僅需一擊就能完成鍛造，鍛擊產(chǎn)生的極大壓力迫使金屬成型。模具可以是分離組裝的，也可以把所有模腔都放在一個坯體內(nèi)。小型鍛件使用獨立模具更加方便。大型金屬錠 的鍛造現(xiàn)在幾乎都用液壓壓力機而不用蒸汽錘，因為壓力機產(chǎn)生的功可以作用得更加深透。而且壓力機可以加工較冷的金屬錠，得到更加精確的尺寸。</p><p>　　鍛造溫度基本與軋制相同，也可以像軋制那樣改善金屬的物

84、理性能。重要的是終鍛時鋼坯不能太熱，因為過熱的鋼坯冷卻后，其機械性能較差。為鍛件加熱，通常用肉眼判斷溫度，但在生產(chǎn)大量相同鍛件的場合，應(yīng)該在有溫度計指示溫度的爐子中加熱要鍛造的坯件，并且常常采用自動控制。</p><p><b>　　3.焊接</b></p><p>　　焊接技術(shù)已經(jīng)變得如此通用以致今天定義“焊接”都感到困難。以前說焊接是“用熔焊把金屬連接起來”，就是

85、靠熔融，但這一定義已經(jīng)不再適用。后來又曾定義焊接為“用加熱把金屬連接起來”，但這也不十分準(zhǔn)確。因為不僅金屬能焊接，許多塑料也能焊接。而且，有些焊接并不需要加熱。每個機械工作者都熟悉無熱焊接以及某些情況下使用的冷壓焊。此外還有聲焊和使人滿意的激光焊。面對年復(fù)一年日益增多的各種各樣的焊接方法，我們這里必須采用如下的焊接定義：“焊接不是無需用緊固裝置耳連接金屬和塑料的方法”。</p><p>　　沒有一個給各種焊接工藝

86、統(tǒng)一命名的方法。有些焊接工藝根據(jù)熱源或防護方法來命名。另一些特許工藝是功呢?fù)?jù)焊縫的形式來命名的，例如電焊和對接焊。但整體分類不能這樣考慮，因為類型同樣的焊縫焊接工藝可能并不相同。例如電焊可以應(yīng)用電阻、電弧、電子束等工藝，對接焊可用電阻焊、燒焊或其它的方法。許多焊接工藝根據(jù)加熱的方法、使用的設(shè)備、所連接金屬的種類以及焊縫的強度來命名。</p><p>　　錫焊是要用熔融狀態(tài)的第三種金屬把兩件金屬連接在一起的工藝。焊

87、料主要由錫和鉛組成，并經(jīng)常用鉍和鎘降低熔點。錫焊最重要的工序之一是清理焊縫表面，可以用某種酸洗劑來進行。錫焊能在輕型鋼件、銅件和黃銅件上產(chǎn)生滿意的焊縫，但強度比銅焊、鉚焊和焊接弱。這些金屬焊接方法通常用于生產(chǎn)強固持久的焊縫。</p><p>　　壓力焊是把兩件金屬焊在一起的最簡單的方法。用火焰把金屬兩端加熱到白熾狀態(tài)，鐵的焊接溫度為1300℃左右，在這個溫度下，金屬變成塑料性材料，通過施壓或錘擊使兩端結(jié)合在一起，

88、最后將焊縫清理平整。在焊接前必須首先注意表面完全清潔，因為贓物會削弱焊縫強度。此外，鋼鐵加熱到高溫會引起氧化，在加熱表面形成氧化皮。因此，加熱金屬需施加助焊劑。焊接加熱時，氧化物粒子與任何其它可能存在的雜質(zhì)一起熔融在助焊劑中。金屬表面被壓合在一起時，助焊劑從焊縫中間被擠出。</p><p>　　氣焊使用各種氣體獲得熱焰。通常使用乙炔、天然氣及氫氣與氧氣的混合氣體。氧氫焰的焊接溫度最高可達(dá)3600°F(1

89、980℃)。電解水或者使用蒸汽通過焦炭上方都可以產(chǎn)生氫氣。氧乙炔焊通過氧的燃焰加熱，使用或者不使用金屬焊絲。多數(shù)情況下焊縫被加熱至熔融狀態(tài)，通常不必加壓。</p><p>　　電弧焊是一種依靠電弧產(chǎn)生的熱進行連接的工藝。電極或者填充金屬被加熱到液態(tài)，然后填充至連接處形成焊縫。首先將電極與工件接觸形成電流回路，然后把焊條與工件分開形成電弧。電流的能量被轉(zhuǎn)換成電弧的熱量，溫度可達(dá)到10 000°F(5500

90、℃)。電流可以用交流電或直流電，但多數(shù)情況下首選的是直流電。直流電焊機就是一臺能量恒定的直流發(fā)電機，產(chǎn)生穩(wěn)定的電弧。電弧焊一般使用金屬或碳棒電極。</p><p>　　激光焊的應(yīng)用主要是由于激光的熱強度很高。由于激光傳遞能量的形式是光，所以可以在任何透明的材質(zhì)中操作，并且與工件不接觸。焊接時能量傳遞是同通過脈沖而不是連續(xù)的光束進行的。激光束集中在焊接的工件上，高熱使焊縫熔融。激光焊接所需的時間較長，僅僅用于特殊加

91、工，包括一些小件焊接，主要用于電子工業(yè)。</p><p>　　爆炸焊用炸藥爆炸產(chǎn)生的能量焊接金屬。爆炸使金屬加速、碰撞并粘接在一起，焊接時間用不了一秒鐘，不必使用金屬填料。焊接實質(zhì)在室溫下進行，工件整體溫度并不升高。但焊縫表面的金屬被碰撞的能量加熱，焊接通過金屬表面的塑性流動而完成。隨著爆炸及其產(chǎn)生的力從焊縫的一端推進到另一端，焊接逐漸進行。焊件的變形與焊縫的類型有關(guān)。某些焊件的變形根本不明顯，沒有金屬損失。&l