機械設計及其理論畢業(yè)設計外文翻譯資料

1、英文原文名English for Die Mould Design and Manufacturing中文譯名模具設計與制造專業(yè)英語英文原文版出處：模具設計與制造專業(yè)英語，劉建雄 王家惠 廖丕博 主編，北京大學出版社2006年3月第1版 譯文：33壓鑄壓鑄是通過壓力作用下使熔融金屬進入金屬模具，是快速生產精密產品的一部分。這個術語同時適用于所得的鑄件。壓鑄件因為具有有良好的表面而可以經濟地應用于批量和大批量生產中。只需要相對小的加工，就可以實現(xiàn)很好的公差保證，這些原則在一些壓鑄操作中都得到了很好的檢驗。壓鑄模具是永久性的，不會由于金屬的引入而影響到他們，除正常磨損或損耗。在相同的大小和形狀的條

2、件下，壓鑄模通常比塑料模和永久鑄造更昂貴。這種快速成型依靠快速把金屬注入模具、冷卻、開模、鑄件取出和模具下次壓鑄的準備。331模具壓鑄周期在鑄造周期里，首先模具閉合并且鎖緊，熔化的金屬在一個特定溫度的熔爐中，然后進入注射缸，根據(jù)合金的類型，用于熱壓室或者冷壓室金屬澆注系統(tǒng)，這些將在后面描述。在注射階段的壓鑄過程中，熔融金屬在壓力的作用下，快速通過模具澆注系統(tǒng)進入模具并排出模具里的空氣，金屬量必須足夠大以充滿型腔和溢流井，溢流井的設計是用來儲存接收溢流出來的融溶金屬液的，因為接觸到模具型腔的空氣容易氧化，同時也最先接觸到模具其也可以快速冷卻以便可以接下來進行第二次的壓鑄。一旦這模具型腔填滿了，作

3、用于金屬液的壓力會增大，保壓一定的時間以便金屬液凝固，模具的分離、工件的取出通常通過機器自動操作完成，打開模具進行必要的清理和潤滑，然后下一輪壓鑄繼續(xù)循環(huán)。從模具取下的工件冷卻后，操作工切除金屬澆注填充時產生的披鋒，同時去除溢流井和分型線，接著能進行二次加工和表面后處理。332壓鑄合金四類主要的壓鑄模具合金為鋅、鋁、鎂和銅基合金，壓鑄工藝發(fā)展于19世紀鉛/錫合金零件的制作，然而，鉛和錫由于力學性能差，現(xiàn)在很少用來壓鑄。最常見的壓鑄合金是鋁合金，它們密度低，耐腐蝕性好，易于鑄造，并具有良好的力學性能和尺寸穩(wěn)定性。鋁合金的缺點是用冷壓室鑄造時比熱壓室鑄造需要更長的周期因為需要一個分離澆注操作。鋅基

4、合金是最容易鑄造的，它們也有很高的延展性和良好的抗沖擊強度，因此可廣泛用于產品上，鑄件可以制造得很薄，并且表面平滑性良好，使其易于電鍍和噴涂。然而，鋅基合金容易被腐蝕，需要在零件各部分涂上保護膜。因此，鋅合金的高比重導致每個單位體積的鋅合金比壓鑄鋁合金要更貴。鋅鋁合金的鋁含量（82.7%）比標準鋅合金高，類似于標準鋅合金，能獲得薄壁和耐久的壓鑄件，但與鋁合金，在冷壓室機器中必須每個周期都需要澆注熔融金屬，唯一例外的是ZA8（8%鋁），這是鋁鋅系列中含鋁量最低的。鎂合金有較低的密度、高的強度重量比、優(yōu)越的阻尼能力和良好的機械加工性能。銅基合金、黃銅和青銅，比任何壓鑄合金的力學性能都要好，但是它們

5、更貴。黃銅具有高的強度和韌性、好的耐磨性，并具有優(yōu)良的耐腐蝕性。銅基合金鑄造的一個主要缺點是在非常高的鑄造溫度下由熱疲勞引起模具壽命縮短，合金澆注溫度對模具壽命影響最為強烈，也正是因為這個原因模具壽命最長的是鋅合金，最短的是銅合金。然而，鑄件尺寸、壁厚和幾何復雜性同樣影響模具表面的磨損和最終的損壞也是差不多的。333壓鑄模具壓鑄模具由兩個主要部分組成動模部分和定模部分，它們在分型線閉合，型腔和型芯通常加工后鑲嵌到這兩部分，定模固定在定模扳上，而動模固定在動模板上（見圖3-10，3-11），型腔和型芯設計必須匹配以便能夠順利開模。壓鑄模具的結構幾乎與注塑成型模具相似，在注射成型術語中，動模包括型

6、芯和噴射器殼體，定模包括型腔和支撐板。壓鑄模鑄件側抽芯機構與外部相交特征可以非常精準地建立起來，這是壓鑄模和注塑模相同的特性。然而，熔模鑄造合金在模具接觸表面的粘性遠遠小于注射成型的。這種現(xiàn)象被稱為“噴射”，容易堵塞模具，正是因為這個原因，結合飛邊的高收縮力導致局部收縮非常困難，使得產品難以滿足內部核心機制。因此，內螺紋或其他內部切削孔通常無法被鑄造，必須由昂貴的額外加工生產。澆注系統(tǒng)在壓鑄和注塑模具中的建立是相同的?！皣娚洹苯洺Ｔ诙：蛣幽Ｖg產生，在產品分型線上形成一些薄而不規(guī)則的披鋒，有時，這些分型線會濺出合金，由于這個原因，壓鑄機必須安裝安全裝置以抑制這些濺出的材料。在壓鑄過程中的一個

7、區(qū)別主要在于溢流井通常圍繞壓鑄型腔的周邊，如前面所提到的，在鑄造時它們可以減少氧化物的量，最先進入模具的合金，通過排氣孔把型腔內的空氣排出，隨后注射的合金和模具有更高的溫度，從而減少金屬凝固過早的機會，這種過早凝固形成的表面缺陷稱為冷料，是由于金屬流動時還沒有相遇熔接在一起就已經凝固所致，當壓鑄模較小時，溢流槽大幅增加熔融金屬也可以使模具保持一定的溫度。3.3.4壓鑄機1.熱室壓鑄機 一個典型的熱室注射系統(tǒng)如圖3-12所示，由氣缸、柱塞、流道和噴嘴組成，注塑周期開始時的柱塞在相應的位置上，熔融金屬流入保溫爐內，通過進氣口并進入壓力缸，然后，當模具合模并鎖緊時，液壓柱塞移動到氣缸和密封進氣口，熔

8、融金屬通過流道和噴嘴到澆口、澆注系統(tǒng)和模具模腔，澆口是噴嘴通過進料系統(tǒng)進入定模的錐形擴流通道，錐形狀提供從澆注點到澆注流道的平滑過渡，這使凝固后的產品容易脫出。在預設的金屬凝固時間里，液壓系統(tǒng)使柱塞返回，這個周期循環(huán)往復。2.冷室壓鑄機一個典型的冷室壓鑄機如圖3-13所示，由水冷式柱塞，一個壓射缸，和位于上方的水平式注射室和一個澆注孔組成。操作順序如下：當模具關閉和鎖緊并且氣缸柱塞縮回，熔融金屬通過澆注孔被澆進注射室，為了包緊型腔里的金屬液，金屬的澆注體積大于型腔和澆注系統(tǒng)、溢流井的體積，然后注射氣缸加壓，使活塞通過注射室，使熔融金屬進入模具型腔，在金屬凝固后，模具打開，柱塞返回到原來的位置。

9、當模具打開，在注射筒端多余的金屬，被稱為料柄，是被逼出來的，因為它是連接到缸體鑄件。在壓鑄周期中料柄是需要的，用于保持液態(tài)金屬的壓力鑄造、凝固和收縮。第4章 鍛造模具4.1 簡介鍛造是一個通過各種模具和工具施加壓力到工件加工的方法，這是最古老的金屬加工方法，至少可以追溯到公元前4000年，也許早在公元前8000年，鍛造通過用石頭錘擊金屬用來制造珠寶、錢幣和各種器具。簡單的鍛造操作，傳統(tǒng)上由鐵匠用重錘子和砧進行。然而，大多數(shù)鍛件需要一套模具和壓力機或鍛錘等設備完成。典型的鍛造產品有螺栓和鉚釘、連桿、渦輪機軸、齒輪、有手柄的工具、機械構件、飛行器、鐵路和各種其它運輸設備。通過控制金屬的流動和晶粒結

10、構，可以鍛造具有良好的強度和韌性的零件；它們能夠可靠地用于高強度工序（如圖4-1）。鍛造可在室溫（冷鍛）或在高溫（熱鍛，取決于溫度）進行。由于該材料的強度較高，冷鍛需要更大的力量，工件的材料在室溫下必須具有足夠的延展性，冷鍛造件具有良好的表面光潔度和尺寸精度。熱鍛需要較小的力量，但它產生的尺寸精度和表面光潔度較差。鍛件通常需要額外的后處理操作，例如熱處理以修改其性能，然后加工以得到準確的成品尺寸，這些操作可以通過精密鍛造，是一個趨向最終形狀或近終形狀成型過程的重要例子，這種顯著減少加工，降低產品制造成本的方法，是今后發(fā)展的趨勢。有幾種形式的鍛造，但還是有一些差異識別過程與名字在不同的引用。4.

11、2 開式模鍛開式模鍛是最簡單的鍛造工藝，雖然大多數(shù)開放式模鍛一般重達15公斤500公斤，但是也有鍛重300噸的，大小的范圍可以從非常小的零件到長達23米（如螺旋槳）。開模鍛過程可以描述為由固體工件放置在兩個平面之間通過壓縮它降低高度（如圖4-2），這個過程也被稱為鐓粗或平鍛。模具表面在開式模鍛可以簡單鑄造，生產相對簡單的鍛件。在理想的條件下對工件的變形如圖4-2（b）所示，因為鍛件體積恒定，在高度方向減少，在直徑方向就會增加。需要注意的是，在圖4-2（b）中，所述工件是均勻地變形，而在實際操作中，工件變成桶形（如圖4-2 （c），這種變形也被稱為鐓鍛。快速移動造成主要由摩擦力形成接口,反的材料

12、在這些接口對流?？焖僖苿涌梢杂行Ю脻櫥瑒?。把加熱后的工件放在冷模之間鍛造同樣能變成圓桶形，在界面的部分迅速冷卻，而工件的其余部分仍然相對較熱，因此，在工件的端部的材料具有變形比在其中心處的材料高的阻力，所以在工件的中心部分沿橫向擴展比端部大，可以通過熱效應使用加熱的金屬模具減少或消除圓桶效應，熱障如在模具和工件接觸面之間使用玻璃纖維也是可行的。引伸鍛造也稱為拔長，是一個基于開式模鍛并通過間隔連續(xù)鍛造工序減小棒料厚度的操作（如圖4-3所示），因為每次行程的接觸面積較小，一條長的棒料不需要很大的力或者機器就能減小其厚度。鐵匠用錘子和砧加工加熱的金屬工件，各種設計的鐵柵欄通常用這種方法制成。4.3

13、 模鍛和閉式模鍛在模鍛里，工件通過在兩個有所需形狀的模具型腔（鍛模）中成形（如圖4-4所示），需要注意的是一些材料向外流動，并形成一些飛邊。飛邊有一個顯著的作用在流動的材料進入模鍛時：薄的飛邊快速冷卻，并且由于其摩擦力，這使得材料在模具型腔中受到高的壓力，從而促進模具型腔的填充。坯件通過這些方法制備（a）切割或剪切一條擠壓或拉伸的棒料（b）粉末冶金制作型坯（c）鑄造或者（d）在鍛造前預先成形毛坯。坯件放在下模，然后上模開始下降，坯件的形狀逐漸改變，如圖4-5（a）所示為一個連桿鍛造。預制坯鍛造過程如拔長和滾壓（如圖4-5（b）和（c）通常用于將材料分配到不同坯件區(qū)域，就像它們是面團制作餡餅。拔

14、長時，材料從一個區(qū)域分配，滾壓時，材料聚集在一個局部區(qū)域里，然后將部件形成為連桿的粗糙形狀稱為預鍛過程，使用預鍛模，最后的操作是在鍛造金屬模具給予鍛造件最終形狀的精加工，飛邊通常通過修整操作去除（如圖4-6所示）。如圖4-4和4-5（a）所示的例子被稱為閉式模鍛。然而，真正的閉式?；蛘呙呭懺?，飛邊不形成并且工件完全填充模腔（如右圖4-7（b）所示）。精確控制材料體積和適當?shù)哪＞咴O計是為了閉式模鍛獲得所需尺寸和公差。尺寸不足的坯料阻礙完全填充模腔，相反尺寸有余的坯料產生過多的壓力并且可能引起模具過早地失效或者卡住。4.3.1精密鍛造出于經濟原因，當今鍛造加工的趨勢是朝著更大的精確度發(fā)展，從而降

15、低了額外精加工操作的數(shù)量。其中形成的部分接近于所需零件的最終尺寸稱為近凈形狀或者凈形鍛造，在這樣的過程中，有少量過量的材料在鍛造部件上，并且它隨后被去除（通常通過修整或磨削）。在精密鍛造，特別模具生產零件比模鍛精度更高并要求更少的加工，該方法需要更高性能的設備因為得到精細部件需要更大的力。由于它們需要相對低的鍛造負載和溫度，鋁和鎂的合金特別適用于精密鍛造，同時發(fā)生模具磨損小，表面光潔度好，鋼和鈦也可以精密鍛造。典型精密鍛造產品有齒輪、連桿、外殼和渦輪葉片。精密鍛造需要特殊和更復雜的模具，精密控制坯料的體積和形狀，坯料在模腔內精確定位，因此投入較高。然而更少的材料被浪費，并且需要更小后續(xù)加工，因

16、為該工件接近最終所需的形狀。因此，以往的鍛造與精密鍛造之間的選擇需要一個經濟分析，特別是在考慮到生產數(shù)量時。4.3.2 精壓精壓基本上是一個閉式模鍛過程，通常用來鑄造硬幣、獎章和珠寶（如圖4-8（a）（b）所示），鍛造毛坯在一個完全封閉的模腔里精壓。為了生產精細所需的壓力可以是五或六倍的材料強度，例如，在新鑄幣的細致部分。對于某些工件可能需要幾個精壓操作，潤滑油不能用于精壓中，因為它們能陷入模具型腔中，并且是不能壓縮的，阻止充分再現(xiàn)模具表面細節(jié)。在精壓過程中也使用鍛件和其他的產品，以改善表面光潔度和賦予所需的尺寸精度，這一過程被稱為按尺寸加工，涉及高壓的同時在工件形狀按尺寸加工使用小的變形。制

17、造帶有字母和數(shù)字的工件能夠類似于精壓過程快速完成。原文：3.3 Die Casting Die casting is the art of rapidly producing accurately dimensioned parts by forcing molten metal under pressure into metal dies. The term also applies to the resultant casting. Die castings can be used economically in designs having moderate to large activ

18、ity because the completed piece has a good surface, requires relatively little machining, and can be held to close tolerances. The principles of die casting follow those of good practice in any casting operation. The steel dies are permanent and should not be affected by the metal introduced into th

19、em, except for normal abrasion or wear. Die-casting dies are usually more expensive than those used in plastic or permanent molding of a part of similar size and shape. The rapidity of operation depends upon the speed with which the metal can be forced into the die, cooled, and ejected; the casting

20、removed; and the die prepared for the next shot.3.3.1 The Die Casting Cycle In the casting cycle, first the die is closed and locked. The molten metal, which is main tained by a furnace at a specified temperature, then enters the injection cylinder. Depending on the type of alloy, either a hot-chamb

21、er or cold-chamber metal-pumping system is used. These will be described later. During the injection stage of the die casting process, pressure is applied to the molten metal, which is then driven quickly through the feed system of the die while air escapes from the die through vents. The volume of

22、metal must be large enough to overflow the die cavities and fill overflow wells. These overflow wells are designed to receive the lead portion of the molten metal, which tends to oxidize from contact with air in the cavity and also cools too rapidly from initial die contact to produce sound castings

23、. Once the cavities are filled, pressure on the metal is increased and held for a specified dwell time during which solidification takes place. The dies are then separated, and the part extracted, often by means of automatic machine operation. The open dies are then cleaned and lubricated as needed,

24、 and the casting cycle is repeated. Following extraction from the die, parts are often quenched and then trimmed to remove the runners, which were necessary for metal flow during mold filling. Trimming is also necessary to remove the overflow wells and any parting-line flash that is produced. Subseq

25、uently, secondary machining and surface finishing operations may be performed. 3.3.2 Die Casting Alloys The four major types of alloys that are die-cast are zinc, aluminum, magnesium, and copper-based alloys. The die casting process was developed in the 19th century for the manu- facture of lead/tin

26、 alloy parts. However, lead and tin are now very rarely die-cast because of their poor mechanical properties. The most common die casting alloys are the aluminum alloys. They have low density, good corrosion resistance, are relatively easy to cast, and have good mechanical properties and dimensional

27、 stability. Aluminum alloys have the disadvantage of requiring the use of cold-chamber machines, which usually have longer cycle times than hot-chamber machines owing to the need for a separate ladling operation. Zinc-based alloys are the easiest to cast. They also have high ductility and good impac

28、t strength, and therefore can be used for a wide range of products. Castings can be made with very thin walls, as well as with excellent surface smoothness, leading to ease of preparation for plating and painting. Zinc alloy castings, however, are very susceptible to corrosion and must usually be co

29、ated, adding significantly to the total cost of the component. Also, the high specific gravity of zinc alloys leads to a much higher cost per unit volume than for aluminum die casting alloys.Zinc-aluminum (ZA) alloys contain a higher aluminum content (82.7%) than the standard zinc alloys. Thin walls

30、 and long die lives can be obtained, similar to standard zinc alloys, but as with aluminum alloys, cold-chamber machines, which require pouring of the molten metal for each cycle, must usually be used. The single exception to this rule is ZA8 (8% Al), which has the lowest aluminum content of the zin

31、c-aluminum family. Magnesium alloys have very low density, a high strength-to-weight ratio, exceptional damping capacity, and excellent machinability properties. Copper-based alloys, brass and bronze, provide the best mechanical properties of any of the die casting alloys; but they are much more exp

32、ensive. Brasses have high strength and toughness, good wear resistance, and excellent corrosion resistance. One major disadvantage of copper-based alloy casting is the short die life caused by thermal fatigue of the dies at the extremely high casting temperatures. Die life is influenced most strongl

33、y by the casting temperature of the alloys, and for that reason is greatest for zinc and shortest for copper alloys. However, this is only an approximation since casting size, wall thickness, and geometrical complexity also influence the wear and eventual breakdown of the die surface.3.3.3 Die Casti

34、ng Dies Die casting dies consist of two major sectionsthe ejector die half and the cover die halfwhich meet at the parting line. The cavities and cores are usually machined into inserts that are fitted into each of these halves. The cover die half is secured to the stationary platen, while the eject

35、or die half is fastened to the movable platen (see Figs. 3-10, 3-11). The cavity and matching core must be designed so that the die halves can be pulled away from the solidified casting. The construction of die casting dies is almost identical to that of molds for injection molding. In injection mol

36、ding terminology, the ejector die half comprises the core plate and ejector housing, and the cover die half comprises the cavity plate and backing support plate. Side-pull mechanisms for casting parts with external cross-features can be found in exactly the same form in die casting dies as in plasti

37、c injection molds. However, molten die casting alloys are much less viscous than the polymer melt in injection molding and have a great tendency to flow between the contacting surfaces of the die. This phenomenon, referred to as “flashing”, tends to jam mold mechanisms, which must, for this reason,

38、be robust. The combination of flashing with the high core retraction forces due to part shrinkage makes it extremely difficult to produce satisfactory internal core mechanisms. Thus, internal screw threads or other internal undercuts cannot usually be cast and must be produced by expensive additiona

39、l machining operations. Ejection systems found in die casting dies are identical to the ones found in injection molds.“Flashing” always occurs between the cover die and ejector die halves, leading to a thin, irregular band of metal around the parting line. Occasionally, this parting line flash may e

40、scape between the die faces. For this reason, full safety doors must always be fitted to manual die casting machines to contain any such escaping flash material.One main difference in the die casting process is that overflow wells are usually designed around the perimeter of die casting cavities. As

41、 mentioned earlier, they reduce the amount of oxides in the casting, by allowing the first part of the shot, which displaces the air through the escape vents, to pass completely through the cavity. The remaining portion of the shot and the die are then at a higher temperature, thereby reducing the c

42、hance of the metal freezing prematurely. Such premature freezing leads to the formation of surface defects called cold shuts, in which streams of metal do not weld together properly because they have partially solidified by the time they meet. Overflow wells are also needed to maintain a more unifor

43、m die temperature on small castings, by adding substantially to the mass of molten metal.3.3.4 Die Casting Machines 1. Hot-Chamber Machines A typical hot-chamber injection or shot system, as shown in Fig. 3-12, consists of a cylinder, a plunger, a gooseneck, and a nozzle. The injection cycle begins

44、with the plunger in the up position. The molten metal flows from the metal-holding pot in the furnace, through the intake ports, and into the pressure cylinder. Then, with the dies closed and locked, hydraulic pressure moves the plunger down into the pressure cylinder and seals off the intake ports.

45、 The molten metal is forced through the gooseneck channel and the nozzle and into the sprue, feed system, and die cavities. The sprue is a conically expanding flow channel that passes through the cover die half from the nozzle into the feed system. The conical shape provides a smooth transition from

46、 the injection point to the feed channels and allows easy extraction from the die after solidification. After a preset dwell time for metal solidification, the hydraulic system is reversed and the plunger is pulled up. The cycle then repeats.2. Cold-Chamber Machines A typical cold-chamber machine, a

47、s shown in Fig. 3-13, consists of a horizontal shot chamber with a pouring hole on the top, a water-cooled plunger, and a pressurized injection cylinder. The sequence of operations is as follows: when the die is closed and locked and the cylinder plunger is retracted, the molten metal is ladled into

48、 the shot chamber through the pouring hole. In order to tightly pack the metal in the cavity, the volume of metal poured into the chamber is greater than the combined volume of the cavity, the feed system, and the overflow wells. The injection cylinder is then energized, moving the plunger through t

49、he chamber, thereby forcing the molten metal into the die cavity. After the metal has solidified, the die opens and the plunger moves back to its original position. As the die opens, the excess metal at the end of the injection cylinder, called the biscuit, is forced out of the cylinder because it i

50、s attached to the casting. Material in the biscuit is required during the die casting cycle in order to maintain liquid metal pressure on the casting while it solidifies and shrinks.Chapter 4 Forging Die 4.1 Introduction Forging is a process in which the workpiece is shaped by compressive forces app

51、lied through various dies and tools. It is one of the oldest metalworking operations, dating back at least to 4000 B.C.perhaps as far back as 8000 B.C. Forging was first used to make jewelry, coins, and various implements by hammering metal with tools made of stone. Simple forging operations can be

52、performed with a heavy hand hammer and an anvil, as was traditionally done by blacksmiths. Most forgings, however, require a set of dies and such equipment as a press or a forging hammer.Typical forged products are bolts and rivets, connecting rods, shafts for turbines, gears, hand tools, and struct

53、ural components for machinery, aircraft, railroads, and a variety of other transportation equipment. Metal flow and grain structure can be controlled, so forged parts have good strength and toughness; they can be used reliably for highly stressed and critical applications (Fig. 4-1). Forg- ing may b

54、e done at room temperature (cold forging) or at elevated temperatures (warm or hot forging, depending on the temperature).Because of the higher strength of the material, cold forging requires greater forces, and the workpiece materials must have sufficient ductility at room temperature. Cold-forged

55、parts have good surface finish and dimensional accuracy. Hot forging requires smaller forces, but it produces dimensional accuracy and surface finish that are not as good. Forgings generally require additional finishing operations, such as heat treating, to modify properties, and then machining to o

56、btain accurate finished dimensions. These operations can be minimized by precision forging, which is an important example of the trend toward net-shape or near-net shape forming processes. This trend significantly reduces the number of operations required, and hence the manufacturing cost to make th

57、e final product.There are several forms of forging, but there is some disparity identifying processes with names in different references.4.2 Open-Die Forging Open-die forging is the simplest forging process. Although most open-die forging generally weighs 15 kg500 kg, forging as heavy as 300 tons ha

58、ve been made. Sizes may range from very small parts up to shafts some 23 m long (in the case of ship propellers).The open-die forging process can be depicted by a solid workpiece placed between two flat dies and reduced in height by compressing it (Fig. 4-2). This process is also called upsetting or

59、 flat-die forging. The die surfaces in open-die forging may have simple cavities, to produce relatively simple forgings. The deformation of the workpiece under ideal conditions is shown in Fig. 4-2 (b). Because constancy of volume is maintained, any reduction in height increases the diameter of the

60、forged part.Note that, in Fig. 4-2 (b), the workpiece is deformed uniformly. In actual operations, the part develops a barrel shape (Fig. 4-2 (c); this deformation is also known as pancaking. Barreling is caused primarily by frictional forces at the die-workpiece interfaces that oppose the outward f