外文翻译--锻压

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. 锻 压 锻造是通过锤击或者压挤而使金属成形。锻造时金属先行加热 有时加热到很高的温度。在现代工业中大规模的锻造常常称做“压制”，但压制这一个术语也可以指金属薄板的冷冲压，或者，实际上是指压制任何材料。然而，本文只说金属。 尽管所有的锻造都是从古代铁匠锻打马蹄铁的方法 发展而来的，而现在已经有种类繁多的压力机来进行锻造，有一些压力机用来制造象顶针这样小的零件，还有一些压力机则用来生产大型远洋轮船螺旋桨轴这样大的部件。做这种用途的压力机的体积是很大的并能产生很大的压力。最大的能产生十万吨以上的压力。 锻压有两个要点应该弄清楚。第一，金属尽管是固体，实际上是能够流动的，同非常粘的液体的流动没有很大的不同。如果不具有这种性质，金属就不能锻造，并且当压力机开始把它压成所需要的形状时就会断裂。第二，与机加工不同，机加工是金属切削成形，而锻压是利用金属的塑性，把金属压挤成形而根本不切 削金属。 锻造 最早的压力机是用来进行锻造的，它直接从铁匠的锤打和铁砧演变出来的。可能所有的压力机的起源都是汽锤。它利用蒸汽的力量把一个很重的锤头升起来，然后让它落到被锻制的金属上。汽锤所完成的工作完全和铁匠的铁锤相同，但是它是靠蒸汽的力量来升起捶头，所以具有远为巨大的锻压能力。 现代的锻压机能锻制重量达到 200 吨的锻件，但是这么大的压力机通常是用液体来传动的，既用油压是锻锤压下。如果所成形的金属件要成批量的生产，可以采用一种“模锻”的方法。锤头和砧座上都装有一个模具，既一个挖空的模子。把金属加热使它有更大 的塑性而更加容易成形，再放到砧座上的模具里面。然后把锤头下降到放在两个模子之间的金属上加压，从而压挤成所需要的形状。模具本身是很昂贵的，但是一旦装好以后，成批量的生产的效率很高。典型的模锻锻件有汽车的曲轴和连杆，齿轮毛坯（在齿形未切出以前的粗制齿轮）和蒸汽涡轮的叶片。金属锻造前加热的程度随所用的金属和加工的工件的类型的不同而异。 金属块不仅能够锻制成一定的形状，而且也可以在两个模具之间沿着其长度方向来进行挤压使之镦粗。这种方法最初用来镦螺栓头，而现在用于许多需要把一段金属镦粗的各种场合。 挤压 用这种方法， 是把实心圆柱形的金属或者“坯料”放在专门的压力机上，在液压滑块的极大的压力作用下象挤牙膏一样，把金属从一个具有选定孔型的模子里边挤出来。某些较软的金属比如铅可以冷挤压，但是许多金属必需使用热挤压。这种方法可以用来制造管子，棒材以及各种实心和空心的零件。这种方法也可以用于把一层金属包在别的部件上 例如电缆外层的铅皮。 冲压 压力机也可以用来给金属板冲孔以及许多类似的用途。我们称之为压床的机器有大的也有小的，大的可以是一台很大的机器，小的可以安装在工作台上。 冲孔的基本原理是把金属放在机器工作台上凹模的上面，然后在动力作用下使压力机带