锻造论文文献翻译#中英文翻译#外文翻译匹配

沈阳理工大学学位论文 27 附录 A 英文原文 A.1 FORGING Bulk defirnnation of metals refers to various processes, such as forging, rolling, or extruding, where there is a controlled plastic flow or working of metals into useful shapes. The most well known of these processes is forging where deformation is accomplished by means of pressure, impact blows, or a combination of both. Hammer Forging Hanuner forging consists of striking the hot metal with a large semiautomatic hammer. If no dies are involved, the forging will be dependent mainly on the skill of the operator. If closed or impression dies are used, one blow is struck for each of several (lie cavities. A- gain, productivity and quality depend to a large degree on the skill of the hanimer operator and the tooling. Press Forging Press forging is characterized by a slow squeezing action. Again, open or closed dies may be used. The open dies are used chiefly for large, simple-geometry parts that are later machined to shape. Closed-die forging relies less on operator skill awl more on the design of the preform and forging dies.2 As an example of the versatility of the process, newer developments have made it possible to produce bevel gears with straight or helical teeth. Rotation of the die (luring penetration will press bevel gears with spiral teeth. Open-die Forging Open-die forging is distinguished by the fact that the metal is never completely confined as it is shaped by various dies. Most open-die forgings are produced on flat, V, or swaging dies. Round swaging (lies and V dies are used in pairs or with a flat die. The top (lie is attached to the ram of the press, and the bottom die is attached to the hammer anvil or, in the case of press open-die forging, to the press bed. As the workpiece is hammered or pressed, it is repeatedly manipulated between the dies until hot working forces the metal to the final dimensions, as-shown in Fig. 1. After forging, the part is rough- and finished-machined. As an example of the amount of material allowed 沈阳理工大学学位论文 28 for machining, a 6.5 in. diameter shaft would have to be forged to 7.4 in. dianieter. In open-die forging of steel, a rule of thumb says that 50 lb of falling weight is required for each square inch of cross section. Impression-die Forging In the simplest example of impression-die forging, two dies are brought together, and the workpiece undergoes plastic deformation until its enlarged sides touch the side walls of the die (Fig. 2). A small amount of material is forced outside the die impression, forming flash that is gradually thinned. The flash cools rapidly and presents increased resistance to deformation, effectively becoming a part of the tool, and helps build up l)ressUre inside the bulk of the work- piece that aids material flow into unfilled impressions. 沈阳理工大学学位论文 29 Closed-die forgings, a special form of impression-die forging, does not depend on the formation of flash to achieve complete filling of the (lie. Thus closed-die forging is considerably more demanding on die design. Since pressing is often completed in one stroke, careful control of the workpieee volume is necessaiy to achieve complete filling without generating extreme pressures in the dies from overfilling. Extrusion Forging As with upsetting, extrusion forging is often accomplished by cold working. Three principal types of metal displacement by plastic flow are involved. Backward and forward, tube, and impact extrusion are shown in Fig. 3. The metal is placed in a container and corn- pressed by a ram movement until pressure inside the metal reaches flow-stress levels. The workpiece completely fills the container, and additional pressure causes it to leave through an orifice and form the extruded product. Extruded products may be either solid or hollow shapes. Tube extrusion is used to produce hollow shapes such as containers and pipes. Reverse-impact extrusion is used for mass production of aluminum cans. The ram hits a slug of metal in the die at high impact, usually 15 times the yield strength of the metal, which causes it to flow instantaneously up the walls of the die. Other common hollow extrusion products are aerosol cans, lipstick cases, flashlight cases, and vacuum bottles. Secondary operations, such as heading, thread rolling, dimpling, and machining, are often needed to complete the items. 沈阳理工大学学位论文 30 Generally steel impacts are limited to 2.5 times the punch diameter. Hydraulic presses are used for loads of over 2000 tons because they have a greater variation in stroke length, speed, and other economic advantages. Tolerances vary with materials arid design, hut production runs calling for 0.002- to 0.005-in, tolerance are regularly made. Roll Forging Roll forging in its simplest form consists of a heated billet passing between a pair of rolls that deform it along its length (Fig. 8-4). Compared to conventional rolling processes, the rolls are relatively small in diameter and serve as an arbor into which the forging tools are secured. The active surface of the tool occupies only a portion (usually half) of the roll circumference to accommodate the full cross section of the stock. The reduction of the cross section obtainable in one pass is limited by the tendency of the material to spread and form an undesirable flash that may be forged into the surface as a defect in the subsequent operations. The workpiece is int roduced repeatedly with 90 rota- tion between passes. Ring Rolling Ring rolling offers a homogeneous circumferential grain flow, ease of fabrication and machining, and versatility of material size . Manu- facture of a rolled ring starts with a sheared blank, which is forged to a pancake, punched, and pierced. There is no limit to the size of the rolled rings, ranging from roller-bearing sleeves to Fig. 4 Roll forging rings 25 ft in diameter with face heights of 80 in. Various profiles may be rolled by suitably shaping the driven, idling rolls. 沈阳理工大学学位论文 31 CAD/CAM in Forging CAD/CAM is being increasingly applied to frging. Using the three-dimensional description of a machined part, which may have been computer designed, it is possible to generate the geometry of the associated forging. Thus the forging sections can be obtained from a common (laiR base. Using well-known techniques, forging loads and stresses can be obtained and flash dimensions can be selected for each section where metal flow is approximated as ro dimensional (plane strain or axisymmetric ). In some relatively simple section geomethes, computer simulation can be conducted to evaluate initial guesses on preform sections. Once the preform geometry has been developed to the designers satisfaction, this geometric data base can utilized to write NC part programs to obtain the NC tapes or disks for machining. A.2 HEAT TREATMENT OF METAL Annealing The word anneal has been used before to describe heat-treating processes for softening and regaining ductility in connection with cold working of material. It has a similar meaning when used in connection with the heat treating of allotropic materials. The purpose of full annealing is to decrease hardness, increase ductility, and sometimes improve machinability of high carbon steels that might otherwise be difflcult to cut. The treatment is also used to relieve stresses, refine grain size, and promote uniformity of structure throughout the material. Machinability is not always improved by annealing. The word machinability is used to describe several interrelated factors, including the ability of a material to be cut with a good surface finish. Plain low carbon steels, when fully annealed, are soft and relatively weak, offering little resistance to cutting, but usually having sufficient ductility and toughness that a cut chip tends to puli and tear the surface from which it is removed, leaving a comparatively poor quality surface, which results in a poor machinability rating. For such steels annealing may not be the most suitable treatment. The machinability of many of the higher plain carbon and most of the alloy steels can usually be greatly improved by annealing, as they are often too hard and strong to be easily cut at any but their softest condition . 沈阳理工大学学位论文 32 The procedure for annealing hypoeutectoid steel is to heat slowly to approximately 60 C above the Ac3 line, to soak for a long enough period that the temperature equalizes throughout the material and homogeneous austenite is formed, and then to allow the steel to cool very slowly by cooling it in the furnace or burying it in lime or some other insulating material. The slow cooling is essential to the precipitation of the maximum ferrite and the coarsest pearlite to place the steel in its softest, most ductile, and least strained condition. Normalizing The purpose of normalizing is somewhat similar to that of annealing with the exceptions that the steel is not reduced to its softest condition and the pearlite is left rather fine instead of coarse. Refinement of grain size, relief of internal stresses, and improvement of structural uniformity together with recovery of some ductility provide high toughness qualities in normalized steel. The process is frequently used for improvement of machinability and for stress nlief to reduce distortion that might occur with partial machining or aging. The procedure for normalizing is to austenitize by slowly heating to approximately C80 above the Ac3 or Accm3 temperature for hypoeutectoid or hypereuteetoid steels, respectively; providing soaking time for the formation of austenite; and cooling slowly in still air. Note that the steels with more carbon than the eutectoid composition are heated above the Aom instead of the Ac used for annealing. The purpose of normalizing is to attempt to dissolve all the cementite during austenitization to eliminate, as far as possible, the settling of hani, brittle iron carbide in the grain boundaries. The desired decomposition products are smallgrained, fine pearlite with a minimum of free ferrite and free cementite. Spheroidizing Minimum hardness and maximum ductility of steel can he produced by a process called spheroidizing, which causes the iron carbide to form in small spheres or nodules in a ferrite matrix, in order to start with small grains that spheroid ize more readily, the process is usually performed on normalized steel. Several variations of processing am used, but all reqllin the holding of the steel near the A1 temperature (usually slightly below) for a number of hours to allow the iron carbide to form on its more stable and lower energy state of small, rounded glohules. The main need for the process is to improve the machinability quality of high carbon 沈阳理工大学学位论文 33 steel and to pretreat hardened steel to help produce greater structural uniformity after quenching. Because of the lengthy treatment time and therefore rather high cost, spheroidizing is not performed nearly as much as annealing or normalizing. Hardening of Steel Most of the heat treatment hardening processes for steel are basel on the production of high pereentages of martensite. The first step. therefore, is that used for most of the other heat-treating processes-treatment to produce austenite. Hypoeutectoid steels are heated to approximately 60CC above the Ac3 temperature and allowed to soak to obtain temperature unifonnity and austenite homogeneity. Hypereutectoid steels are soaked at about 60CC above the A1 temperature, which leaves some iron carbide present in the material. The second step involves cooling rapidly in an attempt to avoid pearlite transformation by missing the nose of the i-T curve. The cooling rate is determined by the temperature and the ability of the quenching media to carry heat away from the surface of the material being quenched and by the conduction of heat through the material itself. Table1 shows some of the commonly used media and the method of application to remove heat, arranged in order of decreasing cooling ability. High temperature gradients contribute to high stresses that cause distortion and cracklug, so the quench should only as extreme as is necessary to produce the desired structure. Care must be exercised in quenching that heat is removed uniformly to minimize thermal stresses. 沈阳理工大学学位论文 34 For example, a long slender bar should be end-quenched, that is, inserted into the quenching medium vertically so that the entire section is subjected to temperature change at one time. if a shape of this kind were to be quenched in a way that caused one side to drop in temperature before the other, change of dimensions would likely cause high stresses producing plastic flow and permanent distortion. Several special types of quench are conducted to minimize quenching stresses and decrease the tendency for distortion and cracking. One of these is called martempering and consists of quenching an austenitized steel in a salt at a temperature above that needed for the start of martensite formation (Ms). The steel being quenched is held in this bath until it is of uniform temperature but is removed before there is time for fonnation of bainite to start. Completion of the cooling in air then causes the same hard martensite that would have formed with quenching from the high temperature, but the high thermal or quench stresses that are the primary source of cracks and warping will have been eliminated. A similar process performed at a slightly higher temperature is called austempering. In this case the steel is held at the bath temperarnre for a longer period, and the result of the isothermal treatment is the formation of bainite. The bainite structure is not as hard as the martensite that could be formed from the same composition, but in addition to reducing the thermal shock to which the steel would be subjected under normal hardening procedures, ii is unnecessary to perform any further treatment to develop good impact resistance in the high hardness range Tempering A third step usually required to condition a hardened steel for service is tempering, or as it is sometimes referred to, drawing. With the exception of austempered steel, which is frequently used in the as-hardened condition, most steels are not serviceable “as quenched”. The drastic cooling to produce martensite causes the steel to be very hard and to contain both macroscopic and microscopic internal stresses with the result that the material has little ductility and extreme brittleness. Reduction of these faults is accomplished by reheating the steel to some point below the A1 (lower transformation) temperature. The stnictural changes caused by tempering of hardened steel are functions of both time and temperature, with temperature being the most important. It should be emphasized that tempering is not a 沈阳理工大学学位论文 35 hardening process, but is, instead, the reverse. A tempered steel is one that has been hardened by heat treatment and then stress relieved, softened, and provided with increased ductility by reheating in the tempering or drawing procedure. The magnitude of the structural changes and the change of properties caused by tempering depend upon the temperature to which the steel is reheated. The higher the ternperatun, the greater the effect, so the choice of temperature will generally depend on willingness to sacrifice hardness and strength to gain ductility and toughness. Reheating to below lOOt has little noticeable effect on hardened plain carbon steel. Between lO(YC and 200T, there is evidence of some structural changes. Above 200T marked changes in structure and properties appear. Prolonged heating at just under the A1 temperature will result in a spheroidized structure similar to that produced by the spheroidizing process. In commercial tempering the temperature range of 25O-425 is usually avoided because of an unexplained embrittlement, or loss of ductility, that often occun with steels ternpered in this range. Certain alloy steels also develop a temper brittleness in the tempera- ture range of 425-600 C , particularly when cooled slowly from or through this range of temperature. When high temperature tempering is necessary for these steels, they are usually heated to above 600 C and quenched for rapid cooling. Quenches from this temperature, of course, do not cause hardening because austenitization has not been accomplished. 沈阳理工大学学位论文 36 附录 B 汉语 翻译 B.1 锻造 金属变形方法有多种，比如通过锻造、滚压或挤压，使金属的塑性流动或加工受到控制而得到有用的形状。这些方法中最广为人知的是锻造，它通过压力、冲击或两者的组合使材料变形。 锤锻 锤锻是用大的半自动锻锤锻打热金属，如果不用模具，锻造主要取决于操作者的技巧。如使用封闭模或型腔模，对几个模膛的每一个模膛都要锤打一次。同样地，生产率和质量在很大程度上取决于锤锻操作者的技巧和所用工具。 锻压 锻压具有缓慢加压的特点，同样可用开模或封闭模。开模主要用于大型的形状简单的零件，锻压后再 加工成形。封闭模锻造很少依赖操作者的技巧，而更多地取决于预成形模和锻模的设计。例如，目前能用直齿或螺旋齿加工锥齿轮，加工过程中旋转的模具用螺旋齿挤压出锥齿轮。 开模锻 开模锻的显着特征是：用不同模具成形时，金属没有被完全限制。大多数开模锻使用平砧、 V 形砧或 U 型砧模一圆形砧和 V 形砧成对使用或和一个平砧一起使用，上模装在压力机的压头上，下模装在锤砧上，开模压力锻时装在压力机床身上。 锤锻或压锻时，将工件在模具间重复锻打，直至金属达到最终尺寸，如图 l 所示。锻打后，零件再粗加工和精加工，作为 一个加工余量的实例，一根直径 6 . 5 英寸的轴的锻打直径为 7 . 4 英寸。 在钢的开模锻中，一个经验数据是每平方英寸横截面需 50 磅锻击力。 型腔模锻 型腔模锻的最简单实例是，将两个模具相互靠拢，其间的工件经受塑性变形直至其周边充满模具为止（图 2 ）。少量材料被压出型模膛，形成薄薄的飞边。飞边迅速冷却，增加了变形阻力，变成了模具的一部分，帮助在工件内部产生压力，使材料流至未填充的型腔。 封闭模锻是一种特殊的型腔模锻，不依赖飞边的形成，叮完整充填模具。因此，封沈阳理工大学学位论文 37 闭模锻更多地依赖于模具设计。因压锻经常 在一次冲程中完成，因此应仔细控制工件体积，做到既能完全充填，在模具中又不产生多余压力，使材料滋出。 挤压锻造 如同冷墩，挤压常通过冷加工完成。挤压锻主要有三种形式的金属塑性流动，即正与反挤压、管挤压和冲击挤压，如图 3 所示：将金属置于容器中，通过压头移动加压直至金属内部压力达到流动应力。金属完全填满容器，进一步加压导致金属通过小孔流出，形成挤压产品。 挤压产品既可以是实心件也可以是空心件。管挤压用来制造空心产品，如容器和管道。反向冲击挤压用于铝罐的大批量生产，压头高速冲击模具中的金属原料，通常，应力 是金属屈服强度的巧倍，这使金属瞬间成形。其他常用的空心挤出产品是气雾罐，唇膏筒，电筒壳和真空瓶，它们经常需要进一步的加工，比如卷边，螺纹滚压，做出波纹和机加工来完成产品制作。 通常，钢的冲击限制在冲头直径的 2 . 5 倍以内。由于行程长度、速度等其有较大的变化范围及其他经济优点，液压机用于载荷超过 2000 吨场合。公差随材料和设计而变，但生产上通常需要 0.002 0.005 英寸的公差 . 辊轧锻造 最简单的辊轧锻造是将 根加热的棒通过一对轧辊，使其沿长度方向变形（图 8 一4 ）与传统棍轧过程相比 ，辊轧锻造的轧辊直径较小，相当于安装锻打工具的心轴。工具的工作表面只占轧辊圆周的一部分（通常一半），来容纳棒料的整个横截面。 棒料辊锻一次的横截面减少量受到材料扩展和形成不必要的毛边的限制，毛边可能被压进锻件表面，在后续操作中形成缺陷，工件每重复送进轧辊一次，都要转 90 度。 环状轧制 环状轧制可得到均质的周向纤维流，易于制造和加工，可用于多种尺寸。要将原材料制成一个，先要卜料