1、秋風清，秋月明,落葉聚還散,寒鴉棲復驚。攀枝花學院本科畢業設計（論文）外文譯文院 （系）： 機電工程學院 專 業： 機械設計制造及其自動化 姓 名： 王 中 蔚 學 號： ZJD02043 指導教師評語： 簽名： 年 月 日外語文獻翻譯摘自: 制造工程與技術（機加工）（英文版） Manufacturing Engineering and TechnologyMachining 機械工業出版社 2004年3月第1版 美 s. 卡爾帕基安(Serope kalpakjian) s.r 施密德(Steven R.Schmid) 著原文：20.9 MACHINABILITYThe machinabil

2、ity of a material usually defined in terms of four factors:1、 Surface finish and integrity of the machined part;2、 Tool life obtained;3、 Force and power requirements;4、 Chip control. Thus, good machinability good surface finish and integrity, long tool life, and low force And power requirements. As

3、for chip control, long and thin (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by becoming entangled in the cutting zone.Because of the complex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinab

4、ility of a material. In manufacturing plants, tool 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. Machinability Of SteelsBecause steels are a

5、mong the most important engineering materials (as noted in Chapter 5), their machinability has been studied extensively. The machinability of steels has been mainly improved by adding lead and sulfur to obtain so-called free-machining steels.Resulfurized and Rephosphorized steels. Sulfur in steels f

6、orms manganese sulfide inclusions (second-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 of these inclusions significantly influence

7、machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfurized steels.Phosphorus in steels has two major effects. It strengthens the ferrite, causing increased hardness. Harder steels result in better chip formation and

8、 surface finish. Note that soft steels can be difficult to machine, with built-up edge 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.Leaded Steels. A high percent

9、age 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, and aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubr

10、icant (Section 32.11) and is smeared over the tool-chip interface during cutting. This behavior has been verified by the presence of high concentrations of lead on the tool-side face of chips when machining leaded steels.When the temperature is sufficiently high-for instance, at high cutting speeds

11、and feeds (Section 20.6)the lead melts directly in front of the tool, 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, 11xx, 12xx, 4

12、1xx, etc. Leaded steels are identified by the letter L between the second and third numerals (for example, 10L45). (Note that in stainless steels, similar use of the letter L means “low carbon,” a condition that improves their corrosion resistance.)However, because lead is a well-known toxin and a p

13、ollutant, there 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 lead in steels (lead-free steels). Bismuth and tin are now being inv

14、estigated as possible substitutes for lead in steels.Calcium-Deoxidized Steels. An important development is calcium-deoxidized steels, 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

15、and wear. Temperature is correspondingly reduced. Consequently, these steels produce less crater wear, especially at high cutting speeds.Stainless Steels. Austenitic (300 series) steels are generally difficult to machine. Chatter can be s problem, necessitating machine tools with high stiffness. How

16、ever, ferritic stainless steels (also 300 series) have good machinability. Martensitic (400 series) steels are abrasive, tend to form a built-up edge, and require tool materials with high hot hardness and crater-wear resistance. Precipitation-hardening stainless steels are strong and abrasive, requi

17、ring hard and abrasion-resistant tool materials.The Effects of Other Elements 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 compounds inc

18、rease tool wear and reduce machinability. It is essential to produce and use clean steels.Carbon and manganese have various effects on the machinability of steels, depending on their composition. Plain low-carbon steels (less than 0.15% C) can produce poor surface finish by forming a built-up edge.

19、Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Tool and die 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 reduces the t

20、endency for built-up edge formation.Other alloying elements, 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 have particularly detrimental

21、 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 ratio and the higher the machinability.In selecting various elements to improve machinability, we should con

22、sider the possible detrimental effects of these elements on the properties and strength of the machined part in service. At elevated temperatures, for example, lead causes embrittlement of steels (liquid-metal embrittlement, hot shortness; see Section ), although at room temperature it has no effect

23、 on mechanical properties.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 temperature, the mechanical properties of resulfurized steels depend on the orientation of the defor

24、med manganese sulfide inclusions (anisotropy). Rephosphorized steels are significantly less ductile, and are produced solely to improve machinability. Machinability of Various Other Metals Aluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting

25、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 tool materials. Dimensional tolerance control may be a problem in machining aluminum,

26、 since it has a high thermal coefficient of expansion and a relatively low elastic modulus.Beryllium is similar to cast irons. Because it is more abrasive and toxic, though, it requires machining in a controlled environment.Cast gray irons are generally machinable but are. Free carbides in castings

27、reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials.Cobalt-based alloys are abrasive and highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds

28、 and speeds.Wrought copper can be difficult to machine because of built-up edge formation, although cast 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.Magnesium is v

29、ery 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).Molybdenum is ductile and work-hardening, so it can produce poor surface finish. Sharp tools are necessary.

30、Nickel-based alloys are work-hardening, abrasive, and strong at high temperatures. Their machinability is similar to that of stainless steels.Tantalum is very work-hardening, ductile, and soft. It produces a poor surface finish; tool wear is high.Titanium and its alloys have poor thermal conductivit

31、y (indeed, the lowest of all metals), causing significant temperature rise and built-up edge; they can be difficult to machine.Tungsten is brittle, strong, and very abrasive, so its machinability is low, although it greatly improves at elevated temperatures.Zirconium has good machinability. It requi

32、res a coolant-type cutting fluid, however, because of the explosion and fire. Machinability of Various MaterialsGraphite is abrasive; it requires hard, abrasion-resistant, sharp tools.Thermoplastics generally have low thermal conductivity, low elastic modulus, and low softening temperature. Conseque

33、ntly, machining them requires tools with positive rake angles (to reduce cutting forces), large relief angles, small depths of cut and feed, relatively high speeds, and proper support of the workpiece. Tools should be sharp.External cooling of the cutting zone may be necessary to keep the chips from

34、 becoming “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 annealed for a period of time at temperatures ranging from to (to), and

35、then cooled slowly and uniformly to room temperature.Thermosetting plastics are brittle and sensitive to thermal gradients during cutting. Their machinability is generally similar to that of thermoplastics.Because of the fibers present, reinforced plastics are very abrasive and are difficult to mach

36、ine. Fiber tearing, 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 debris to avoid contact with and inhaling of the fibers.The m

37、achinability of ceramics has improved steadily with the development of nanoceramics (Section ) and with the selection of appropriate processing parameters, such as ductile-regime cutting (Section 22.4.2).Metal-matrix and ceramic-matrix composites can be difficult to machine, depending on the propert

38、ies of the individual components, i.e., reinforcing or whiskers, as well as the matrix material. Thermally Assisted MachiningMetals and alloys that are difficult to machine at room temperature can be machined more easily at elevated temperatures. In thermally assisted machining (hot machining), the

39、source of heata torch, induction coil, high-energy beam (such as laser or electron beam), or plasma arcis forces, (b) increased tool life, (c) use of inexpensive cutting-tool materials, (d) higher material-removal rates, and (e) reduced tendency for vibration and chatter.It may be difficult to heat

40、and maintain a uniform 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-strength metals and alloys, although experiments are in progress

41、to machine ceramics such as silicon nitride. SUMMARYMachinability is usually defined in terms 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 c

42、ontrol of process variables.譯文：20.9 可機加工性一種材料的可機加工性通常以四種因素的方式定義：1、 分的表面光潔性和表面完整性。2、刀具的壽命。3、切削力和功率的需求。4、切屑控制。以這種方式，好的可機加工性指的是好的表面光潔性和完整性，長的刀具壽命，低的切削力和功率需求。關于切屑控制，細長的卷曲切屑，如果沒有被切割成小片，以在切屑區變的混亂，纏在一起的方式能夠嚴重的介入剪切工序。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可機加工性的關系。在制造廠里，刀具壽命和表面粗糙度通常被認為是可機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

43、在以下的例子中能夠被看到。 鋼的可機加工性因為鋼是最重要的工程材料之一（正如第5章所示），所以他們的可機加工性已經被廣泛地研究過。通過宗教鉛和硫磺，鋼的可機加工性已經大大地提高了。從而得到了所謂的易切削鋼。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引起應力。其結果是使切屑容易斷開而變小，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，其化學性質與硫類似，在二次硫化鋼中起夾雜物改性作用。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，形成更好的切屑形成和表面光潔性。需要注意的是軟鋼不適合用于有

44、積屑瘤形成和很差的表面光潔性的機器。第二個影響是增加的硬度引起短切屑而不是不斷的細長的切屑的形成，因此提高可加工性。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，被涂在刀具和切屑的接口處。這一特性已經被在機加工鉛鋼時，在切屑的刀具面表面有高濃度的鉛的存在所證實。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，鉛降低第一剪切區中的剪應力，減小切削力和功率消耗。鉛能用于各種鋼號，例如10XX，11XX，12X

45、X，41XX等等。鉛鋼被第二和第三數碼中的字母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）。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境隱患（在鋼產品中每年大約有4500噸的鉛消耗）。結果，對于估算鋼中含鉛量的使用存在一個持續的趨勢。鉍和錫現正作為鋼中的鉛最可能的替代物而被人們所研究。脫氧鈣鋼 一個重要的發展是脫氧鈣鋼，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中的力量，降低刀具和切屑接口處的摩擦和磨損。溫度也相應地降低。結果，這些鋼產生更小的月牙洼磨損，特別是在高切削速度時更是如此

46、。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可機加工性。馬氏體鋼易磨蝕，易于形成積屑瘤，并且要求刀具材料有高的熱硬度和耐月牙洼磨損性。經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。鋼中其它元素在可機加工性方面的影響 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，降低可機加工性。因此生產和使用凈化鋼非常必要。根據它們的構成，碳和錳鋼在鋼的可機加工性方面有不同的影響。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潔性。盡管鑄鋼的可

47、機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。大多數鋼的可機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。其它合金元素，例如鎳、鉻、鉗和釩，能提高鋼的特性，減小可機加工性。硼的影響可以忽視。氣態元素比如氫和氮在鋼的特性方面能有特別的有害影響。氧已經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，就產生越低的縱橫比和越高的可機加工性。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，見節），盡管其在室溫下對力學性能沒有影響。因為硫化鐵的構成，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構的形成。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