機械加工外文文獻翻譯

1、<p><b>　　外文原文</b></p><p>　　MACHINABILITY</p><p>　　The machinability of a material usually defined in terms of four factors:</p><p>　　Surface finish and integrity of

2、 the machined part;</p><p>　　Tool life obtained;</p><p>　　Force and power requirements;</p><p>　　Chip control. </p><p>　　Thus, good machinability good surface finish an

3、d integrity, long tool life, and low force And power requirements. As for chip control, long and thin (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by becoming entangled in th

4、e cutting zone.</p><p>　　Because of the complex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinability of a material. In manufacturing plants, t

5、ool life and surface roughness are generally considered to be the most important factors in machinability. Although not used much any more, approximate machinability ratings are available in the example below.</p>

6、<p>　　1、Machinability Of Steels</p><p>　　Because steels are among the most important engineering materials (as noted in Chapter 5), their machinability has been studied extensively. The machinability o

7、f steels has been mainly improved by adding lead and sulfur to obtain so-called free-machining steels.</p><p>　　Resulfurized and Rephosphorized steels. Sulfur in steels forms manganese sulfide inclusions (s

8、econd-phase particles), which act as stress raisers in the primary shear zone. As a result, the chips produced break up easily and are small; this improves machinability. The size, shape, distribution, and concentration

9、of these inclusions significantly influence machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfuriz</p><p>　　Phosphorus i

10、n steels has two major effects. It strengthens the ferrite, causing increased hardness. Harder steels result in better chip formation and surface finish. Note that soft steels can be difficult to machine, with built-up e

11、dge formation and poor surface finish. The second effect is that increased hardness causes the formation of short chips instead of continuous stringy ones, thereby improving machinability.</p><p>　　Leaded St

12、eels. A high percentage of lead in steels solidifies at the tip of manganese sulfide inclusions. In non-resulfurized grades of steel, lead takes the form of dispersed fine particles. Lead is insoluble in iron, copper, an

13、d aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubricant (Section 32.11) and is smeared over the tool-chip interface during cutting. This behavior has been verified by the

14、 presence of high concentrations of lead on the too</p><p>　　When the temperature is sufficiently high-for instance, at high cutting speeds and feeds (Section 20.6)—the lead melts directly in front of the to

15、ol, acting as a liquid lubricant. In addition to this effect, lead lowers the shear stress in the primary shear zone, reducing cutting forces and power consumption. Lead can be used in every grade of steel, such as 10xx,

16、 11xx, 12xx, 41xx, etc. Leaded steels are identified by the letter L between the second and third numerals (for example, 10L45). (Note</p><p>　　However, because lead is a well-known toxin and a pollutant, th

17、ere are serious environmental concerns about its use in steels (estimated at 4500 tons of lead consumption every year in the production of steels). Consequently, there is a continuing trend toward eliminating the use of

18、lead in steels (lead-free steels). Bismuth and tin are now being investigated as possible substitutes for lead in steels.</p><p>　　Calcium-Deoxidized Steels. An important development is calcium-deoxidized st

19、eels, in which oxide flakes of calcium silicates (CaSo) are formed. These flakes, in turn, reduce the strength of the secondary shear zone, decreasing tool-chip interface and wear. Temperature is correspondingly reduced.

20、 Consequently, these steels produce less crater wear, especially at high cutting speeds.</p><p>　　Stainless Steels. Austenitic (300 series) steels are generally difficult to machine. Chatter can be s problem

21、, necessitating machine tools with high stiffness. However, ferritic stainless steels (also 300 series) have good machinability. Martensitic (400 series) steels are abrasive, tend to form a built-up edge, and require too

22、l materials with high hot hardness and crater-wear resistance. Precipitation-hardening stainless steels are strong and abrasive, requiring hard and abrasion-resistant tool</p><p>　　The Effects of Other Eleme

23、nts in Steels on Machinability. The presence of aluminum and silicon in steels is always harmful because these elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These compoun

24、ds increase tool wear and reduce machinability. It is essential to produce and use clean steels.</p><p>　　Carbon and manganese have various effects on the machinability of steels, depending on their composit

25、ion. Plain low-carbon steels (less than 0.15% C) can produce poor surface finish by forming a built-up edge. Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Tool and die

26、steels are very difficult to machine and usually require annealing prior to machining. Machinability of most steels is improved by cold working, which hardens the material and red</p><p>　　Other alloying ele

27、ments, such as nickel, chromium, molybdenum, and vanadium, which improve the properties of steels, generally reduce machinability. The effect of boron is negligible. Gaseous elements such as hydrogen and nitrogen can hav

28、e particularly detrimental effects on the properties of steel. Oxygen has been shown to have a strong effect on the aspect ratio of the manganese sulfide inclusions; the higher the oxygen content, the lower the aspect ra

29、tio and the higher the machinability.</p><p>　　In selecting various elements to improve machinability, we should consider the possible detrimental effects of these elements on the properties and strength of

30、the machined part in service. At elevated temperatures, for example, lead causes embrittlement of steels (liquid-metal embrittlement, hot shortness; see Section 1.4.3), although at room temperature it has no effect on me

31、chanical properties.</p><p>　　Sulfur can severely reduce the hot workability of steels, because of the formation of iron sulfide, unless sufficient manganese is present to prevent such formation. At room tem

32、perature, the mechanical properties of resulfurized steels depend on the orientation of the deformed manganese sulfide inclusions (anisotropy). Rephosphorized steels are significantly less ductile, and are produced solel

33、y to improve machinability.</p><p>　　2、 Machinability of Various Other Metals </p><p>　　Aluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resul

34、ting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are recommended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive; they require harder

35、tool materials. Dimensional tolerance control may be a problem in machining aluminum, since it has a high thermal coefficient of expansion and a relatively low elastic modulu</p><p>　　Beryllium is similar to

36、 cast irons. Because it is more abrasive and toxic, though, it requires machining in a controlled environment.</p><p>　　Cast gray irons are generally machinable but are. Free carbides in castings reduce thei

37、r machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials.</p><p>　　Cobalt-based alloys are abrasive an

38、d highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds and speeds.</p><p>　　Wrought copper can be difficult to machine because of built-up edge formation, although cast

39、copper alloys are easy to machine. Brasses are easy to machine, especially with the addition pf lead (leaded free-machining brass). Bronzes are more difficult to machine than brass.</p><p>　　Magnesium is ver

40、y easy to machine, with good surface finish and prolonged tool life. However care should be exercised because of its high rate of oxidation and the danger of fire (the element is pyrophoric).</p><p>　　Molybd

41、enum is ductile and work-hardening, so it can produce poor surface finish. Sharp tools are necessary.</p><p>　　Nickel-based alloys are work-hardening, abrasive, and strong at high temperatures. Their machina

42、bility is similar to that of stainless steels.</p><p>　　Tantalum is very work-hardening, ductile, and soft. It produces a poor surface finish; tool wear is high.</p><p>　　Titanium and its alloys

43、 have poor thermal conductivity (indeed, the lowest of all metals), causing significant temperature rise and built-up edge; they can be difficult to machine.</p><p>　　Tungsten is brittle, strong, and very ab

44、rasive, so its machinability is low, although it greatly improves at elevated temperatures.</p><p>　　Zirconium has good machinability. It requires a coolant-type cutting fluid, however, because of the explos

45、ion and fire.</p><p>　　3、Machinability of Various Materials</p><p>　　Graphite is abrasive; it requires hard, abrasion-resistant, sharp tools.</p><p>　　Thermoplastics generally have

46、low thermal conductivity, low elastic modulus, and low softening temperature. Consequently, machining them requires tools with positive rake angles (to reduce cutting forces), large relief angles, small depths of cut and

47、 feed, relatively high speeds, and </p><p>　　proper support of the workpiece. Tools should be sharp.</p><p>　　External cooling of the cutting zone may be necessary to keep the chips from becomin

48、g “gummy” and sticking to the tools. Cooling can usually be achieved with a jet of air, vapor mist, or water-soluble oils. Residual stresses may develop during machining. To relieve these stresses, machined parts can be

49、annealed for a period of time at temperatures ranging from to (to), and then cooled slowly and uniformly to room temperature.</p><p>　　Thermosetting plastics are brittle and sensitive to thermal gradients

50、during cutting. Their machinability is generally similar to that of thermoplastics.</p><p>　　Because of the fibers present, reinforced plastics are very abrasive and are difficult to machine. Fiber tearing,

51、pulling, and edge delamination are significant problems; they can lead to severe reduction in the load-carrying capacity of the component. Furthermore, machining of these materials requires careful removal of machining d

52、ebris to avoid contact with and inhaling of the fibers.</p><p>　　The machinability of ceramics has improved steadily with the development of nanoceramics (Section 8.2.5) and with the selection of appropriate

53、 processing parameters, such as ductile-regime cutting (Section 22.4.2).</p><p>　　Metal-matrix and ceramic-matrix composites can be difficult to machine, depending on the properties of the individual compone

54、nts, i.e., reinforcing or whiskers, as well as the matrix material.</p><p>　　4、Thermally Assisted Machining</p><p>　　Metals and alloys that are difficult to machine at room temperature can be ma

55、chined more easily at elevated temperatures. In thermally assisted machining (hot machining), the source of heat—a torch, induction coil, high-energy beam (such as laser or electron beam), or plasma arc—is forces, (b) in

56、creased tool life, (c) use of inexpensive cutting-tool materials, (d) higher material-removal rates, and (e) reduced tendency for vibration and chatter.</p><p>　　It may be difficult to heat and maintain a un

57、iform temperature distribution within the workpiece. Also, the original microstructure of the workpiece may be adversely affected by elevated temperatures. Most applications of hot machining are in the turning of high-st

58、rength metals and alloys, although experiments are in progress to machine ceramics such as silicon nitride. </p><p><b>　　SUMMARY</b></p><p>　　Machinability is usually defined in term

59、s of surface finish, tool life, force and power requirements, and chip control. Machinability of materials depends not only on their intrinsic properties and microstructure, but also on proper selection and control of pr

60、ocess variables.</p><p><b>　　中文翻譯</b></p><p><b>　　機械加工</b></p><p>　　一種材料的機械加工性通常以四種因素的方式定義：</p><p>　　分的表面光滑度和表面完整性。</p><p><b>

61、;　　2、刀具的壽命。</b></p><p>　　3、力量和功率的需求。</p><p><b>　　4、芯片控制。</b></p><p>　　以這種方式，好的機械加工性指的是好的表面光滑度和完整性，長的刀具壽命，低的力量和功率需求。關于芯片控制，細長的卷曲芯片，如果沒有被切割成小片，以在芯片區(qū)變的混亂，纏在一起的方式能夠嚴重的

62、介入剪切工序。</p><p>　　因為剪切工序的復雜屬性，所以很難建立定量地釋義材料的機械加工性的關系。在制造廠里，刀具壽命和表面粗糙度通常被認為是機械加工性中最重要的因素。盡管已不再大量的被使用，近乎準確的機加工率在以下的例子中能夠被看到。</p><p>　　20.9.1 鋼的機械加工性</p><p>　　因為鋼是最重要的工程材料之一（正如第5章所示），所以

63、他們的機械加工性已經(jīng)被廣泛地研究過。通過宗教鉛和硫磺，鋼的機械加工性已經(jīng)大大地提高了。從而得到了所謂的易切削鋼。</p><p>　　二次硫化鋼和二次磷化鋼 硫在鋼中形成硫化錳夾雜物（第二相粒子），這些夾雜物在第一剪切區(qū)引起應力。其結(jié)果是使芯片容易斷開而變小，從而改善了可加工性。這些夾雜物的大小、形狀、分布和集中程度顯著的影響可加工性?；瘜W元素如碲和硒，其化學性質(zhì)與硫類似，在二次硫化鋼中起夾雜物改性作用。&l

64、t;/p><p>　　鋼中的磷有兩個主要的影響。它加強鐵素體，增加硬度。越硬的鋼，形成更好的芯片形成和表面光滑度。需要注意的是軟鋼不適合用于有積屑瘤形成和很差的表面光滑度的機器。第二個影響是增加的硬度引起短芯片而不是不斷的細長的芯片的形成，因此提高可加工性。</p><p>　　含鉛的鋼 鋼中高含量的鉛在硫化錳夾雜物尖端析出。在非二次硫化鋼中，鉛呈細小而分散的顆粒。鉛在鐵、銅、鋁和它們的合

65、金中是不能溶解的。因為它的低抗剪強度。因此，鉛充當固體潤滑劑并且在切削時，被涂在刀具和芯片的接口處。這一特性已經(jīng)被在機加工鉛鋼時，在芯片的刀具面表面有高濃度的鉛的存在所證實。</p><p>　　當溫度足夠高時—例如，在高的切削速度和進刀速度下—鉛在刀具前直接熔化，并且充當液體潤滑劑。除了這個作用，鉛降低第一剪切區(qū)中的剪應力，減小力量和功率消耗。鉛能用于各種鋼號，例如10XX，11XX，12XX，41XX等等。鉛

66、鋼被第二和第三數(shù)碼中的字母L所識別（例如，10L45）。（需要注意的是在不銹鋼中，字母L的相同用法指的是低碳，提高它們的耐蝕性的條件）。</p><p>　　然而，因為鉛是有名的毒素和污染物，因此在鋼的使用中存在著嚴重的環(huán)境隱患（在鋼產(chǎn)品中每年大約有4500噸的鉛消耗）。結(jié)果，對于估算鋼中含鉛量的使用存在一個持續(xù)的趨勢。鉍和錫現(xiàn)正作為鋼中的鉛最可能的替代物而被人們所研究。</p><p>

67、　　脫氧鈣鋼 一個重要的發(fā)展是脫氧鈣鋼，在脫氧鈣鋼中矽酸鈣鹽中的氧化物片的形成。這些片狀，依次減小第二剪切區(qū)中的力量，降低刀具和芯片接口處的摩擦和磨損。溫度也相應地降低。結(jié)果，這些鋼產(chǎn)生更小的月牙洼磨損，特別是在高切削速度時更是如此。</p><p>　　不銹鋼 奧氏體鋼通常很難機加工。振動能成為一個問題，需要有高硬度的機床。然而，鐵素體不銹鋼有很好的機械加工性。馬氏體鋼易磨蝕，易于形成積屑瘤，并且要求刀

68、具材料有高的熱硬度和耐月牙洼磨損性。經(jīng)沉淀硬化的不銹鋼強度高、磨蝕性強，因此要求刀具材料硬而耐磨。</p><p>　　鋼中其它元素在機械加工性方面的影響 鋼中鋁和矽的存在總是有害的，因為這些元素結(jié)合氧會生成氧化鋁和矽酸鹽，而氧化鋁和矽酸鹽硬且具有磨蝕性。這些化合物增加刀具磨損，降低機械加工性。因此生產(chǎn)和使用凈化鋼非常必要。</p><p>　　根據(jù)它們的構(gòu)成，碳和錳鋼在鋼的機械加工性

69、方面有不同的影響。低碳素鋼（少于0.15%的碳）通過形成一個積屑瘤能生成很差的表面光滑度。盡管鑄鋼的機械加工性和鍛鋼的大致相同，但鑄鋼具有更大的磨蝕性。刀具和模具鋼很難用于機加工，他們通常再煅燒后再機加工。大多數(shù)鋼的機械加工性在冷加工后都有所提高，冷加工能使材料變硬并且減少積屑瘤的形成。</p><p>　　其它合金元素，例如鎳、鉻、鉗和釩，能提高鋼的特性，減小機械加工性。硼的影響可以忽視。氣態(tài)元素比如氫和氮在鋼

70、的特性方面能有特別的有害影響。氧已經(jīng)被證明了在硫化錳夾雜物的縱橫比方面有很強的影響。越高的含氧量，就產(chǎn)生越低的縱橫比和越高的機械加工性。</p><p>　　選擇各種元素以改善可加工性，我們應該考慮到這些元素對已加工零件在使用中的性能和強度的不利影響。例如，當溫度升高時，鋁會使鋼變脆（液體—金屬脆化，熱脆化，見1.4.3節(jié)），盡管其在室溫下對力學性能沒有影響。</p><p>　　因為硫化

71、鐵的構(gòu)成，硫能嚴重的減少鋼的熱加工性，除非有足夠的錳來防止這種結(jié)構(gòu)的形成。在室溫下，二次磷化鋼的機械性能依賴于變形的硫化錳夾雜物的定位（各向異性）。二次磷化鋼具有更小的延展性，被單獨生成來提高機加工性。</p><p>　　20.9.2 其它不同金屬的機加工性</p><p>　　盡管越軟的品種易于生成積屑瘤，但鋁通常很容易被機加工，導致了很差的表面光滑度。高的切削速度，高的前角和高的后角

72、都被推薦了。有高含量的矽的鍛鋁合金鑄鋁合金也許具有磨蝕性，它們要求更硬的刀具材料。尺寸公差控制也許在機加工鋁時會成為一個問題，因為它有膨脹的高導熱系數(shù)和相對低的彈性模數(shù)。</p><p>　　鈹和鑄鐵相同。因為它更具磨蝕性和毒性，盡管它要求在可控人工環(huán)境下進行機加工。</p><p>　　灰鑄鐵普遍地可加工，但也有磨蝕性。鑄造無中的游離碳化物降低它們的機械加工性，引起刀具芯片或裂口。它需要

73、具有強韌性的工具。具有堅硬的刀具材料的球墨鑄鐵和韌性鐵是可加工的。</p><p>　　鈷基合金有磨蝕性且高度加工硬化的。它們要求尖的且具有耐蝕性的刀具材料并且有低的走刀和速度。</p><p>　　盡管鑄銅合金很容易機加工，但因為鍛銅的積屑瘤形成因而鍛銅很難機加工。黃銅很容易機加工，特別是有添加的鉛更容易。青銅比黃銅更難機加工。</p><p>　　鎂很容易機加工

74、，鎂既有很好的表面光滑度和長久的刀具壽命。然而，因為高的氧化速度和火種的危險（這種元素易燃），因此我們應該特別小心使用它。</p><p>　　鉗易拉長且加工硬化，因此它生成很差的表面光滑度。尖的刀具是很必要的。</p><p>　　鎳基合金加工硬化，具有磨蝕性，且在高溫下非常堅硬。它的機械加工性和不銹鋼相同。</p><p>　　鉭非常的加工硬化，具有可延性且柔軟

75、。它生成很差的表面光滑度且刀具磨損非常大。</p><p>　　鈦和它的合金導熱性(的確，是所有金屬中最低的)，因此引起明顯的溫度升高和積屑瘤。它們是難機加工的。</p><p>　　鎢易脆，堅硬，且具有磨蝕性，因此盡管它的性能在高溫下能大大提高，但它的機加工性仍很低。</p><p>　　鋯有很好的機加工性。然而，因為有爆炸和火種的危險性，它要求有一個冷卻性質(zhì)好的

76、切削液。</p><p>　　20.9.3 各種材料的機加工性</p><p>　　石墨具有磨蝕性。它要求硬的、尖的，具有耐蝕性的刀具。</p><p>　　塑性塑料通常有低的導熱性，低的彈性模數(shù)和低的軟化溫度。因此，機加工熱塑性塑料要求有正前角的刀具（以此降低力量），還要求有大的后角，小的切削和走刀深的，相對高的速度和工件的正確支承。刀具應該很尖。</p&g

77、t;<p>　　切削區(qū)的外部冷卻也許很必要，以此來防止芯片變的有黏性且粘在刀具上。有了空氣流，汽霧或水溶性油，通常就能實現(xiàn)冷卻。在機加工時，殘余應力也許能生成并發(fā)展。為了解除這些力，已機加工的部分要在（）的溫度范圍內(nèi)冷卻一段時間，然而慢慢地無變化地冷卻到室溫。</p><p>　　熱固性塑料易脆，并且在切削時對熱梯度很敏感。它的機加工性和熱塑性塑料的相同。</p><p>　

78、　因為纖維的存在，加強塑料具有磨蝕性，且很難機加工。纖維的撕裂、拉出和邊界分層是非常嚴重的問題。它們能導致構(gòu)成要素的承載能力大大下降。而且，這些材料的機加工要求對加工殘片仔細切除，以此來避免接觸和吸進纖維。</p><p>　　隨著納米陶瓷（見8.2.5節(jié)）的發(fā)展和適當?shù)膮?shù)處理的選擇，例如塑性切削（見22.4.2節(jié)），陶瓷器的機械加工性已大大地提高了。</p><p>　　金屬基復合材料

79、和陶瓷基復合材料很能機加工，它們依賴于單獨的成分的特性，比如說增強纖維或金屬須和基體材料。</p><p>　　20.9.4 熱輔助加工</p><p>　　在室溫下很難機加工的金屬和合金在高溫下能更容易地機加工。在熱輔助加工時（高溫切削），熱源—一個火把，感應線圈，高能束流（例如雷射或電子束），或等離子弧—被集中在切削刀具前的一塊區(qū)域內(nèi)。好處是：（a）低的力量。（b）增加的刀具壽命。（c

80、）便宜的切削刀具材料的使用。（d）更高的材料切除率。（e）減少振動。</p><p>　　也許很難在工件內(nèi)加熱和保持一個不變的溫度分布。而且，工件的最初微觀結(jié)構(gòu)也許被高溫影響，且這種影響是相當有害的。盡管實驗在進行中，以此來機加工陶瓷器如氮化矽，但高溫切削仍大多數(shù)應用在高強度金屬和高溫度合金的車削中。</p><p><b>　　小結(jié)</b></p>&