鍛造論文文獻(xiàn)翻譯#中英文翻譯#外文翻譯匹配

沈陽理工大學(xué)學(xué)位論文 27 附錄 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 沈陽理工大學(xué)學(xué)位論文 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. 沈陽理工大學(xué)學(xué)位論文 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. 沈陽理工大學(xué)學(xué)位論文 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. 沈陽理工大學(xué)學(xué)位論文 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 . 沈陽理工大學(xué)學(xué)位論文 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 沈陽理工大學(xué)學(xué)位論文 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. 沈陽理工大學(xué)學(xué)位論文 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 沈陽理工大學(xué)學(xué)位論文 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. 沈陽理工大學(xué)學(xué)位論文 36 附錄 B 漢語 翻譯 B.1 鍛造 金屬變形方法有多種，比如通過鍛造、滾壓或擠壓，使金屬的塑性流動(dòng)或加工受到控制而得到有用的形狀。這些方法中最廣為人知的是鍛造，它通過壓力、沖擊或兩者的組合使材料變形。 錘鍛 錘鍛是用大的半自動(dòng)鍛錘鍛打熱金屬，如果不用模具，鍛造主要取決于操作者的技巧。如使用封閉?；蛐颓荒?，對幾個(gè)模膛的每一個(gè)模膛都要錘打一次。同樣地，生產(chǎn)率和質(zhì)量在很大程度上取決于錘鍛操作者的技巧和所用工具。 鍛壓 鍛壓具有緩慢加壓的特點(diǎn)，同樣可用開?；蚍忾]模。開模主要用于大型的形狀簡單的零件，鍛壓后再 加工成形。封閉模鍛造很少依賴操作者的技巧，而更多地取決于預(yù)成形模和鍛模的設(shè)計(jì)。例如，目前能用直齒或螺旋齒加工錐齒輪，加工過程中旋轉(zhuǎn)的模具用螺旋齒擠壓出錐齒輪。 開模鍛 開模鍛的顯著特征是：用不同模具成形時(shí)，金屬?zèng)]有被完全限制。大多數(shù)開模鍛使用平砧、 V 形砧或 U 型砧模一圓形砧和 V 形砧成對使用或和一個(gè)平砧一起使用，上模裝在壓力機(jī)的壓頭上，下模裝在錘砧上，開模壓力鍛時(shí)裝在壓力機(jī)床身上。 錘鍛或壓鍛時(shí)，將工件在模具間重復(fù)鍛打，直至金屬達(dá)到最終尺寸，如圖 l 所示。鍛打后，零件再粗加工和精加工，作為 一個(gè)加工余量的實(shí)例，一根直徑 6 . 5 英寸的軸的鍛打直徑為 7 . 4 英寸。 在鋼的開模鍛中，一個(gè)經(jīng)驗(yàn)數(shù)據(jù)是每平方英寸橫截面需 50 磅鍛擊力。 型腔模鍛 型腔模鍛的最簡單實(shí)例是，將兩個(gè)模具相互靠攏，其間的工件經(jīng)受塑性變形直至其周邊充滿模具為止（圖 2 ）。少量材料被壓出型模膛，形成薄薄的飛邊。飛邊迅速冷卻，增加了變形阻力，變成了模具的一部分，幫助在工件內(nèi)部產(chǎn)生壓力，使材料流至未填充的型腔。 封閉模鍛是一種特殊的型腔模鍛，不依賴飛邊的形成，叮完整充填模具。因此，封沈陽理工大學(xué)學(xué)位論文 37 閉模鍛更多地依賴于模具設(shè)計(jì)。因壓鍛經(jīng)常 在一次沖程中完成，因此應(yīng)仔細(xì)控制工件體積，做到既能完全充填，在模具中又不產(chǎn)生多余壓力，使材料滋出。 擠壓鍛造 如同冷墩，擠壓常通過冷加工完成。擠壓鍛主要有三種形式的金屬塑性流動(dòng)，即正與反擠壓、管擠壓和沖擊擠壓，如圖 3 所示：將金屬置于容器中，通過壓頭移動(dòng)加壓直至金屬內(nèi)部壓力達(dá)到流動(dòng)應(yīng)力。金屬完全填滿容器，進(jìn)一步加壓導(dǎo)致金屬通過小孔流出，形成擠壓產(chǎn)品。 擠壓產(chǎn)品既可以是實(shí)心件也可以是空心件。管擠壓用來制造空心產(chǎn)品，如容器和管道。反向沖擊擠壓用于鋁罐的大批量生產(chǎn)，壓頭高速?zèng)_擊模具中的金屬原料，通常，應(yīng)力 是金屬屈服強(qiáng)度的巧倍，這使金屬瞬間成形。其他常用的空心擠出產(chǎn)品是氣霧罐，唇膏筒，電筒殼和真空瓶，它們經(jīng)常需要進(jìn)一步的加工，比如卷邊，螺紋滾壓，做出波紋和機(jī)加工來完成產(chǎn)品制作。 通常，鋼的沖擊限制在沖頭直徑的 2 . 5 倍以內(nèi)。由于行程長度、速度等其有較大的變化范圍及其他經(jīng)濟(jì)優(yōu)點(diǎn)，液壓機(jī)用于載荷超過 2000 噸場合。公差隨材料和設(shè)計(jì)而變，但生產(chǎn)上通常需要 0.002 0.005 英寸的公差 . 輥軋鍛造 最簡單的輥軋鍛造是將 根加熱的棒通過一對軋輥，使其沿長度方向變形（圖 8 一4 ）與傳統(tǒng)棍軋過程相比 ，輥軋鍛造的軋輥直徑較小，相當(dāng)于安裝鍛打工具的心軸。工具的工作表面只占軋輥圓周的一部分（通常一半），來容納棒料的整個(gè)橫截面。 棒料輥鍛一次的橫截面減少量受到材料擴(kuò)展和形成不必要的毛邊的限制，毛邊可能被壓進(jìn)鍛件表面，在后續(xù)操作中形成缺陷，工件每重復(fù)送進(jìn)軋輥一次，都要轉(zhuǎn) 90 度。 環(huán)狀軋制 環(huán)狀軋制可得到均質(zhì)的周向纖維流，易于制造和加工，可用于多種尺寸。要將原材料制成一個(gè)，先要卜料