可機加工性英文翻譯

1、原文：1 MACHINABILITYThe machinability 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 lo

2、w 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 the cutting zone.Becauseof the complex nature of cutting operations, it is difficult to establish relationships that

3、quantitatively define the machinability 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.2 Machinab

4、ility Of SteelsBecause steels are among 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 Rephos

5、phorized steels. Sulfur in steels forms 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

6、inclusions significantly influence 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 strengthensthe ferrite, causing increased hardness.Harder steels re

7、sult in better chip formation and 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 machinabili

8、ty.Leaded Steels. 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, and aluminum and their alloys. Because of its low shear strength, ther

9、efore, 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 presence of high concentrations of lead on the tool-side face of chips when machining leaded steels.Calcium-Deoxidized Steels. An important develop

10、ment 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 and wear. Temperature is correspondingly reduced. Consequently, these steels produce less crater wea

11、r, 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. However, ferritic stainless steels (also 300 series) have good machinability. Martensitic (400 series)

12、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, requiring hard and abrasion-resistant tool materials.The Effects of Other Elements in Steels on Machinabi

13、lity. The presence of aluminum and silicon in steels is always harmful becausethese elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These compounds increase tool wear and reduce machinability. It is essential to produce and use clean steels.Carbon and

14、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. Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Too

15、l 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 tendency for built-up edge formation.Other alloying elements, such as nickel, chromium, molybdenum, an

16、d 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 effects on the properties of steel. Oxygen has been shown to have a strong effect on the aspect rati

17、o 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 consider the possible detrimental effects of these elements on the properties and strength of the machin

18、ed part in service.Sulfur can severely reduce the hot workability of steels, because of the formation of iron sulfide, unless sufficient manganeseis present to prevent such formation. At room temperature, the mechanical properties of resulfurized steels depend on the orientation of the deformed mang

19、anese sulfide inclusions (anisotropy). Rephosphorized steels are significantly less ductile, and are produced solely to improve machinability.3 Machinability of Various Other MetalsAluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor

20、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, since i

21、t 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 reduce t

22、heir 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 and spe

23、eds.4 Machi nability of Various MaterialsGraphite is abrasive; it requires hard, abrasi on-resista nt, sharp tools.Thermoplastics gen erally have low thermal con ductivity, low elastic modulus, and low softening temperature. Consequently, machining them requires tools with positive rake angles (to r

24、educe cutting forces), large relief angles, small depths of cut and feed, relatively high speeds, andproper support of the workpiece. Tools should be sharp.Exter nal cooli ng of the cutt ing zone may be n ecessaryto keep the chips from becoming “ gummy and sticking to the tools. Cooling can usually

25、be achieved with a jet of air, vapor mist, or water-soluble oils. Residual stressesmay develop during machining. To relieve these stresses, machined parts can be annealed for a period of time at temperatures ranging from 80 C to 160 C (175 F to315 F ), and then cooled slowly and uniformly to room te

26、mperature.Thermosetting plastics are brittle and sensitive to thermal gradients during cutti ng. Their machi nability is gen erally similar to that of thermoplastics.Because of the fibers prese nt, re in forced plastics are very abrasive and are difficult to mach ine. Fiber teari ng, pulli ng, and e

27、dge delam in ati on are sig nifica nt problems; they can lead to severe reduct ion in the load-carry ing capacity of the comp onent. Furthermore, mach ining of these materials requires careful removal of mach ining debris to avoid con tact with and in hali ng of the fibers.譯文：1 可機加工性 一種材料的可機加工性通常以四種

28、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(guān)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(qū)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(fù)雜屬性， 所以很難建立定量地釋義材料的可機加工性的關(guān) 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在以下的例子中能夠被看到。 2 鋼的可機加工性因為鋼是最重要的工程材料之一(正如第

29、5 章所示)，所以他們的可機加工 性已經(jīng)被廣泛地研究過。 通過宗教鉛和硫磺，鋼的可機加工性已經(jīng)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(qū)引起應(yīng)力。 其結(jié)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?；?學元素如碲和硒，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。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積屑瘤形成和很差 的表面光潔性的機器。 第二個影響是增

30、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(jīng)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。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， 降低刀具和切屑接口處 的摩擦和磨損。溫度也相應(yīng)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

31、時更是如此。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(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。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(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， 降低可機加工性。 因此生產(chǎn)和使用凈化鋼非常必 要。根據(jù)它們的構(gòu)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(shù)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