外文翻譯--鍛壓

FORGING AND PRESSING Forging is the shaping of metal by hammering or squeezing, the metal being heated-sometimes to a high temperature. Large-scale forging in modern industry is often called “pressing”, but this term is also used of the stamping out of thin pieces of cold metal. This article , however ,deals only with metal. Although all forging is based on the blacksmiths ancient method of hammering hi horseshoes into shape , a very wide variety of presses has been developed to carry out this work, some being used to make very small parts, such as a thimble, and others very large ones such as the huge propeller shafts of great ocean liners. Presses for such purposes are enormous and exert a great deal of power. The largest can exert forces of over 100,000 tons. There are two main points to realize about forging and pressing. First, metals, although they are solid, can actually flow in not so different a way from the flow of a very sticky liquid. If it were not for this property, metals could not be pressed, but would break as soon as the press started to form them into the shape required. Secondly, unlike machining where the metal is cut into shape, pressing and forging, by using the plastic property of metals, produce shapes without cutting the metal at all but by squeezing it. Forging. The first presses were for forging and were a direct development of the blacksmiths forge and anvil. Probably the origin of all these was a steam power, and then allowed to drop on to the metal being forged. The steam hammer performed exactly the same kind of work as the blacksmiths hammer but, by making use of steam power to lift the hammer, provided an enormously greater forging capacity. Modern forging presses can make forgings up to 200 tons in weight； but such large presses usually employ hydraulic power transmission, using oil pressure to force down the hammer. When shaped pieces of metal are wanted in large numbers, a process known as drop forging may be used. Both the hammer and he anvil carry a die, or hollowed-out shape. The metal, after being heated to make it more plastic and so more easily formed, is placed in the die of the anvil. The hammer then descends on it, forcing the metal between the two dies and thus squeezing it into the required shape. The dies themselves are very expensive, but once installed they are most efficient for mass production. Typical drop forging are motor-car crankshafts and connecting rods, gear blanks (the rough gearwheel before the teeth have been cut ) , and steam-turbine blades. The degree to which the metal is heated before being forged varies according to the metal used and the type of work being produced. A piece of metal can be not only hammered into a given shape, but also squeezed along its length between dies which cause bulges to occur. This process was first developed for producing the heads on bolts, but it is now used for a number of other purposes where bulges in a length of metal are needed. Extruding. In this method, the metal in the form of a solid cylinder or slug is placed in a special extrusion press and then squeezed out, like toothpaste out of a tube, under very high pressure exerted by a hydraulic ram, through a die with an opening of the chose shape. Some softer metals such as lead can be extruded cold, but many have to be heated. The process is used for producing tubes, rods, and various solid and hollow parts. It can also be used to put a coating of metal on some other part-such as lead cover on an electric cable. Stamping. Presses can also be used for punching holes in sheet metal and for a number of similar purposes. The machines, which are known as stamping presses, range in size from very large machines to small ones mounted on a workbench. The general principle of punching is to place the metal on the tab le of the machine over a die, and then to bring down under power the ram (or hammer) of the press, which carries a punch. This pierces the metal, and moves through the die underneath, thus punching the hole by shearing the metal between the edge of the punch and the die. When the sheet metal on the table is the workpiece, and the piece punched out of form the hole is scrap, this is called punching. The procedure may, however, be reversed , the punch cutting out pieces from the sheet metal of a shape required for some part. When this is done, the piece punched out is the workpiece, and the metal from which it was punched is scarp. In this case, the press is punching out blanks which are the general shape of a part subsequently to be finished by other machining processes, and the procedure is known as blanking. Presses can also be used for bending and forming sheet metal into parts of complex shapes, or embossing the metal with a pattern. Drawing. As well as by forging, punching, or extruding, metal may be formed by being stretched-a process for which drawing presses are used. The metal sheet is stretched over (or draw into ) a die on one side of the sheet by a mating die on the other side, thus producing the desired shape. Bowls, cups, and similar objects can be formed in one piece by this process. The design of dies for deep drawing-that is, drawing parts which are deep as compared with their diameter-is very complicated, and often such drawing has to be carried out in a number of progressive steps. For this work, multiple action presses are used, for these provide the various steps needed to produce the finished drawn part. Presses are now in use which are large enough to produce the roof of a car complete. The bed area of the press may be as large as a small room. Other Methods. Many different methods are used to feed sheet metal to presses for punching or forming； a common method is to feed in the metal continuously from a roll. Also, in order to keep up with the high production speeds needed in modern industry, many different types of automatic and high- speed presses, including dieing machines, have been developed. Some of these have speeds capable of turning out small pressed parts of a highly accurate shape at a rate of 1,000 per minute. The press is the most important machine in the plastics industry, where it is used to squeeze the plastic (often in the form of a power ) into specially shaped moulds to produce the varied types of plastic articles now on the market. Metal powders also are pressed into compacts of various shapes, and are then heated in a furnace-a process known as sintering-till they become a unified piece of metal of the desired shape. This powder metallurgy has a great future, since complicated parts can be pressed in one operation instead of having to be made by a number of lengthy or difficult machining processes. 鍛 壓 鍛造是通過(guò)錘擊或者壓擠而使金屬成形。鍛造時(shí)金屬先行加熱 有時(shí)加熱到很高的溫度。在現(xiàn)代工業(yè)中大規(guī)模的鍛造常常稱做“壓制”，但壓制這一個(gè)術(shù)語(yǔ)也可以指金屬薄板的冷沖壓，或者，實(shí)際上是指壓制任何材料。然而，本文只說(shuō)金屬。 盡管所有的鍛造都是從古代鐵匠鍛打馬蹄鐵的方法 發(fā)展而來(lái)的，而現(xiàn)在已經(jīng)有種類繁多的壓力機(jī)來(lái)進(jìn)行鍛造，有一些壓力機(jī)用來(lái)制造象頂針這樣小的零件，還有一些壓力機(jī)則用來(lái)生產(chǎn)大型遠(yuǎn)洋輪船螺旋槳軸這樣大的部件。做這種用途的壓力機(jī)的體積是很大的并能產(chǎn)生很大的壓力。最大的能產(chǎn)生十萬(wàn)噸以上的壓力。 鍛壓有兩個(gè)要點(diǎn)應(yīng)該弄清楚。第一，金屬盡管是固體，實(shí)際上是能夠流動(dòng)的，同非常粘的液體的流動(dòng)沒有很大的不同。如果不具有這種性質(zhì)，金屬就不能鍛造，并且當(dāng)壓力機(jī)開始把它壓成所需要的形狀時(shí)就會(huì)斷裂。第二，與機(jī)加工不同，機(jī)加工是金屬切削成形，而鍛壓是利用金屬的塑性，把金屬壓擠成形而根本不切 削金屬。 鍛造 最早的壓力機(jī)是用來(lái)進(jìn)行鍛造的，它直接從鐵匠的錘打和鐵砧演變出來(lái)的?？赡芩械膲毫C(jī)的起源都是汽錘。它利用蒸汽的力量把一個(gè)很重的錘頭升起來(lái)，然后讓它落到被鍛制的金屬上。汽錘所完成的工作完全和鐵匠的鐵錘相同，但是它是靠蒸汽的力量來(lái)升起捶頭，所以具有遠(yuǎn)為巨大的鍛壓能力。 現(xiàn)代的鍛壓機(jī)能鍛制重量達(dá)到 200 噸的鍛件，但是這么大的壓力機(jī)通常是用液體來(lái)傳動(dòng)的，既用油壓是鍛錘壓下。如果所成形的金屬件要成批量的生產(chǎn)，可以采用一種“模鍛”的方法。錘頭和砧座上都裝有一個(gè)模具，既一個(gè)挖空的模子。把金屬加熱使它有更大 的塑性而更加容易成形，再放到砧座上的模具里面。然后把錘頭下降到放在兩個(gè)模子之間的金屬上加壓，從而壓擠成所需要的形狀。模具本身是很昂貴的，但是一旦裝好以后，成批量的生產(chǎn)的效率很高。典型的模鍛鍛件有汽車的曲軸和連桿，齒輪毛坯（在齒形未切出以前的粗制齒輪）和蒸汽渦輪的葉片。金屬鍛造前加熱的程度隨所用的金屬和加工的工件的類型的不同而異。 金屬塊不僅能夠鍛制成一定的形狀，而且也可以在兩個(gè)模具之間沿著其長(zhǎng)度方向來(lái)進(jìn)行擠壓使之鐓粗。這種方法最初用來(lái)鐓螺栓頭，而現(xiàn)在用于許多需要把一段金屬鐓粗的各種場(chǎng)合。 擠壓 用這種方法， 是把實(shí)心圓柱形的金屬或者“坯料”放在專門的壓力機(jī)上，在液壓滑塊的極大的壓力作用下象擠牙膏一樣，把金屬?gòu)囊粋€(gè)具有選定孔型的模子里邊擠出來(lái)。某些較軟的金屬比如鉛可以冷擠壓，但是許多金屬必需使用熱擠壓。這種方法可以用來(lái)制造管子，棒材以及各種實(shí)心和空心的零件。這種方法也可以用于把一層金屬包在別的部件上 例如電纜外層的鉛皮。 沖壓 壓力機(jī)也可以用來(lái)給金屬板沖孔以及許多類似的用途。我們稱之為壓床的機(jī)器有大的也有小的，大的可以是一臺(tái)很大的機(jī)器，小的可以安裝在工作臺(tái)上。 沖孔的基本原理是把金屬放在機(jī)器工作臺(tái)上凹模的上面，然后在動(dòng)力作用下使壓力機(jī)帶