【導(dǎo)讀】起著關(guān)鍵性的作用。構(gòu)成物質(zhì)的大約100種?；驹刂校蠹s有一半為金屬。金屬之間的區(qū)別不是特別明顯。些原子相關(guān)聯(lián)的電子的某些特性。它們是熱和電的良導(dǎo)體，不透光。往往具有較高的密度。在外力的作用下可以發(fā)生變化。的撕開金屬原子所需的力那么大。晶性是最重要的。結(jié)晶體是這樣一種結(jié)構(gòu)，佛位于三維棋盤的方格的角上。三維排列的軸線決定了晶體在。在工程實踐中應(yīng)用的金屬由。大量的晶體組成，這些晶體稱之為晶粒。大多數(shù)情況下，晶粒在空間中是自由排列的。在原子范圍內(nèi)，晶粒之間相互接觸緊密結(jié)合。晶粒之間連接區(qū)域被稱為晶界。

　　

【正文】 一方面，如果機器和昂貴，或者質(zhì)量很重要，例如飛機，那麼每一個零件都要設(shè)計計算。 4 The purpose of the design calculations is, of course, to attempt to predict the stress or deformation in the part in order that it may sagely carry the loads, which will be imposed on it, and that it may last for the expected life of the machine. All calculations are, of course, dependent on the physical properties of the construction materials as determined by laboratory tests. A rational method of design attempts to take the results of relatively simple and fundamental tests such as tension, pression, torsion, and fatigue and apply them to all the plicated and involved situations encountered in presentday machinery. 當(dāng)然，設(shè)計計算的目的是試圖預(yù)測零件的應(yīng)力和變形，以保證其安全的帶動負載，這是必要的，并且其也許影響到機器的最終壽命。當(dāng) 然，所有的計算依賴于這些結(jié)構(gòu)材料通過試驗測定的物理性能。國際上的設(shè)計方法試圖通過從一些相對簡單的而基本的實驗中得到一些結(jié)果，這些試驗，例如結(jié)構(gòu)復(fù)雜的及現(xiàn)代機械設(shè)計到的電壓、轉(zhuǎn)矩和疲勞強度。 5 In addition, it has been amply proved that such details as surface condition, fillets, notches, manufacturing tolerances, and heat treatment have a market effect on the strength and useful life of a machine part. The design and drafting departments must specify pletely all such particulars, must specify pletely all such particulars, and thus exercise the necessary close control over the finished product. 另外，可以充分證明，一些細節(jié)，如表面粗糙度、圓角、開槽、制造公差和熱處理都對機械零件的強度及使用壽命有影響。設(shè)計和構(gòu)建布局要完全詳細地說明每一個細節(jié)，并且對最終產(chǎn)品進行必要的測試。 6 As mentioned above, machine design is a vast field of engineering technology. As such, it begins with the conception of an idea and follows through the various phases of design analysis, manufacturing, marketing and consumerism. The following is a list of the major areas of consideration in the general field of machine design: 綜上所述，機械設(shè)計是一個非常寬的工程技術(shù)領(lǐng)域。例如，從設(shè)計理念到設(shè)計分析的每一個階段，制造，市場，銷售。以下是機械設(shè)計的一般領(lǐng)域應(yīng)考慮的主要方面的清單： ① Initial design conception。 最初的設(shè)計理念 ② Strength analysis。受力分析 ③ Materials selection。材料的選擇 ④ Appearance。 外形 ⑤ Manufacturing。制造 ⑥ Safety。安全性 ⑦ Environment effects。環(huán)境影響 ⑧ Reliability and life。 可靠性及壽命 7 Strength is a measure of the ability to resist, without fails, forces which cause stresses and strains. The forces may be: 在沒有破壞的情況下，強度是抵抗引起應(yīng)力和應(yīng)變的一種量度。這些力可能是： ① Gradually applied。漸變力 ② Suddenly applied。瞬時力 ③ Applied under impact。沖擊力 ④ Applied with continuous direction reversals。不斷變化的力 ⑤ Applied at low or elevated 8 If a critical part of a machine fails, the whole machine must be shut down until a repair is made. Thus, when designing a new machine, it is extremely important that critical parts be made strong enough to prevent failure. The designer should determine as precisely as possible the nature, magnitude, direction and point of application of all forces. Machine design is mot, however, an exact science and it is, therefore, rarely possible to determine exactly all the applied forces. In addition, different samples of a specified material will exhibit somewhat different abilities to resist loads, temperatures and other environment conditions. In spite of this, design calculations based on appropriate assumptions are invaluable in the proper design of machine. 如果一個機器的關(guān)鍵件損壞，整個機器必須關(guān)閉，直到修理好為止。設(shè)計一臺新機器時，關(guān)鍵件具有足夠的抵抗破壞的能力是非常重要的。設(shè)計者應(yīng)盡可能準(zhǔn)確地確定所有的性質(zhì)、大小、方向及作用點。機器設(shè)計不是這樣，但精確的科學(xué)是這樣，因此很難準(zhǔn)確地確定所有力。另外，一種特殊材料的不同樣本會顯現(xiàn)出不同的性能，像抗負載、溫度和其他外部條件。盡管如此，在機械設(shè)計中給予合理綜合的設(shè)計計算是非常有用的。 9 Moreover, it is absolutely essential that a design engineer knows how and why parts fail so that reliable machines which require minimum maintenance can be designed. Sometimes, a failure can be serious, such as when a tire blows out on an automobile traveling at high speeds. On the other hand, a failure may be no more than a nuisance. An example is the loosening of the radiator hose in the automobile cooling system. The consequence of this latter failure is usually the loss of some radiator coolant, a condition which is readily detected and corrected. 此外，顯而易見的是一個知道零件是如何和為什麼破壞的設(shè)計師可以設(shè)計出需要很少維修的可靠機器。有時，一次失敗是嚴(yán)重的，例如高速行駛的汽車的輪胎爆裂。另一方面，失敗未必是麻煩。例如，汽車的冷卻系統(tǒng)的散熱器皮帶管松開。這種破壞的后果通常是損失一些散熱片，可以探測并改正過來。 10 The type of load a part absorbs is just as significant as the magnitude. Generally speaking, dynamic loads with direction reversals cause greater difficulties than static loads and, therefore, fatigue strength must be considered. Another concern is whether the material is ductile or brittle. For example, brittle materials are considered to be unacceptable where fatigue is involved. 零件負載類型是一個重要的標(biāo)志。一般而言，變化的動負載比靜負載會引起更大的差異。因此，疲勞強度必須符合。另一個關(guān)心的方面是這種材料是否直或易碎。例如有疲勞 破壞的地方不易使用易碎的材料。 11 In general, the design engineer must consider all possible modes of failure, which include the following: 一般的，設(shè)計師要靠考慮所有破壞情況，其包括以下方面： ① Stress。應(yīng)力 ② Deformation。應(yīng)變 ③ Wear。外形 ④ Corrosion。腐蝕 ⑤ Vibration。震動 ⑥ Environmental damage。外部環(huán)境破壞 ⑦ Loosening of fastening devices. 緊固件的松脫 12 The part sizes and shapes selected must also take into account many dimensional factors which produce external load effects such as geometric discontinuities, residual stresses due to forming of desired contours, and the application of interference fit joints. 零件的尺寸和外形的選擇也有很多因素。外部負荷的影響，如幾何間斷，由于輪 廓而產(chǎn)生的殘余應(yīng)力和組合件干涉。 Unit6 Manufacture Process(1) ComputerAided Manufacturing 1 The scientific study of metalcutting and automation techniques is products of ,he tieth century. Two pioneers of these techniques were Frederick Taylor and Henry Ford. During the early 1900s, the improving U. S. standard of living brought a new high 計算機輔助制造 對金屬切削和自動化技術(shù)的科學(xué)研究時二十世紀(jì)的產(chǎn)物。泰勒和亨利是這些技術(shù)的先驅(qū)。1900 年代早期，美國日益提高的生活水平將個人財富帶到了m pervxi al wealth. The major result was the increased demand for durable goods. This increased demand meant that manufacturing could no longer be treated as a blacksmith trade, and the use of scientific study was employed in manufacturing analysis. Taylor pionee