锻造论文文献翻译

沈阳理工大学学位论文附录A 英文原文A.1 FORGINGBulk 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 ForgingHanuner 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 ForgingOpen-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 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 ForgingIn 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.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 ForgingAs 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. 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 rota- tion between passes. Ring RollingRing 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. 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 METALAnnealingThe 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 .The procedure for annealing hypoeutectoid steel is to heat slowly to approximately 60 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. NormalizingThe 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 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. SpheroidizingMinimum 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 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. 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 rangeTemperingA 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 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, 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 and quenched for rapid cooling. Quenches from this temperature, of course, do not cause hardening because austenitization has not been accomplished.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0.0020.005 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，锻成盘形，再冲孔和贯穿。 对环型坯料的尺寸没有限制，小至轴承套，大到直径25 英尺、面高8 0英寸的圆环。适当地成形被动轧辊和空转轧辊可轧制出不同轮廓的制品。锻造中的CAD/CAM CAD/CAM 已日益应用于锻造之中。利用计算机设计的被加工零件的三维描述，就能生成相关锻件的几何形状。因此，锻件横截面叮通过一个通用数据库获得。使用众所周知的方法，可获得锻击力和应力，对每种截面可选择飞边尺寸，这里金属的流动近似为二维（平面应变和轴对称）。对相对简单的截面形状，可用计算机仿真来评价对预成形横截面的最初设想：一旦预成形的几何形状修改到符合设计者的要求，可用儿何数据库来书写数控加工程序，得到数控加工纸带或磁盘。B.2 金属的热处理退火在前面描述冷拔加工材料的软化并重新获得塑性的热处理方法时，就已经用退火这个词。当用于同素异晶材料的热处理时，该词具有相似的意义。完全退火的目的是降低硬度、增加塑性，有时也提高高碳钢的切削加工性，否则这种钢很难加工。这种热处理方法也用来减少应力，细化晶粒，提高整个材料的结构均匀性。 退火不总是能提高切削加工性，切削加工性一词用来描述几个相关因素，包括材料切削时获得好的表面光洁度（即较小的表面粗糙度值 译者）的能力。，当完全退火时，普通低碳钢硬度较低，强度较小，对切削的阻力较小，但通常由于塑性和韧性太大以致切屑离开工件表面时会划伤表面，工件表面质量比较差，导致较差的切削加工性。对这类钢，退火可能不是最合适的处理方法。许多高碳钢和大多数合金钢的切削加工性通常可经退火大大改善，因为除在最软条件下，它们的硬度和强度太高而不易加工。 亚共析钢的退火方法是将钢缓慢加热到Ac3 线以上大约60 ，保温一段时间，使整个材料温度相同，形成均匀奥氏体，然后随炉或埋在石灰或其他绝缘材料中缓慢冷却。要析出粗大铁素体和珠光体，使钢处于最软、最韧和应变最小的状态，必须缓慢冷却。正火 正火的目的多少类似于退火，但钢不是最软状态且珠光体是细匀而不粗大。钢的正火能细化晶粒，释放内应力，改善结构均匀性同时恢复一些塑性，得到高的韧性。这种方法经常用来改进切削加工性，减少应力，减少因部分切削加工或时效产生的变形。 正火方法是将业析钢或过共析钢分别缓慢加热到Ac3 线或Accm 线上约80 ，保温一段时间以便形成奥氏体，并在静止空气中缓冷。要注意，含碳量超过共析成分的钢要加热到Accm 线以上，而不是退火时的线以下。正火的目的是在奥氏体化过程中试图溶解所有渗碳体，从而尽可能减少晶界上的硬脆铁碳化合物，而得到小晶粒的细珠光体、最小白由铁素体和自由渗碳体。球化退火 通过球化退火可使钢得到最小的硬度和最大的塑性，它可使铁碳化合物以小球状分布在铁素体基体上。为了使小颗粒球化更容易，通常对正火钢进行球化退火。球化退火可用几种不同的方法，但所有方法都需在线温度附近（通常略低）保温很长时间，使铁碳化合物形成更稳定，能级较低的小圆球。 球化退火方法的主要目的是改进高碳钢的切削加性，并对淬硬钢进行预处理，使其淬火后结构更均匀。因为热处理时间长，因此成本高，球化退火不如退火或正火常用。钢的硬化 钢的大多数热处理硬化方法是基于产生高比例的马氏体。因此，第一步用的是大多数其他热处理用的方法 产生奥氏体。亚共析钢加热到温度以下大约60 ，进行保温，使温度均布，奥氏体均匀。过共析钢在线温度以上大约60 时保温，钢中仍残留部分铁碳化合物。 第二步是快速冷却，力图避免在等温曲线鼻部产生珠光休转变。冷却速度取决于温度和淬火时淬火介质从钢表面带走热量的能力以及钢本身传热的能力表11 一1 是一些常用介质和冷却方法，按冷却能力降低的顺序排列。 高的温度梯度产生高应力，会引起变形和开裂，所以淬火只有在非常需要产生特定结构时才使用。淬火时必须小心，使热量均匀扩散以减小热应力。比如，一根细长棒需端部淬火，即将它垂直插进冷却介质中，这样整个截面同时产生温度变化。如果这种形状的工件的某一边比另一边早降温，尺寸变化很可能引起很高的应力，产生塑性流动和永久变形。 用几种特殊的淬火方法可减小淬火应力，减小变形开裂倾向，：一种称为分级淬火，其方法是：将奥氏体钢放人温度高于马氏体转变起始温度（Ms ）的盐浴中，放置一定的时间直到温度均匀，在开始形成贝氏休之前取出，然后放在空气中冷却，产生与从高温开始淬火时同样硬的马氏休，而导致开裂和翘曲的高的热应力或淬火应力已经被消除。 在略高一点温度下的类似方法称为等温淬火，这时，将（奥氏体）钢放在盐浴中，保持很长时间，等温处理的结果是形成贝氏体。贝氏体结构不如在同样成分时形成的马氏休硬，但除了减少钢在正常淬火时受到的热冲击外，不必要进一步处理，就可获得在高硬度时好的冲击韧性。回火 调整淬硬钢以便使用的第三步通常是回火。除了等温淬火钢通常在淬火状态下使用外，大多数钢都不能在淬火