机械加工外文文献翻译

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1、毕业设计（论文）外文翻译 外文原文 MACHINABILITY The 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 to

2、ol 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 the cutting zone. Because of the complex nature of cutting operations, it is difficult to establish re

3、lationships that 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

4、 below. 1、 Machinability Of Steels Because 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. Re

5、sulfurized and Rephosphorized 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 co

6、ncentration of these 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 strengthens the ferrite, causing increased ha

7、rdness. Harder steels result in better chip formation and surface finish. 毕业设计（论文）外文翻译 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 strin

8、gy ones, thereby improving machinability. 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.

9、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 presence of high concentrations of lead on the tool-side face of chips when machining leaded steels. When th

10、e temperature is sufficiently high-for instance, at high cutting speeds 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 consumptio

11、n. Lead can be used in every grade of steel, such as 10xx, 11xx, 12xx, 41xx, 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 c

12、orrosion resistance.) However, because lead is a well-known toxin and a pollutant, 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 us

13、e of lead in steels (lead-free steels). Bismuth and tin are now being investigated 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

14、 the strength of the secondary shear zone, decreasing tool-chip interface 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. Cha

15、tter can be s problem, 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 tool materials with high hot hardness and crater-wear resistan

16、ce. Precipitation-hardening stainless steels 毕业设计（论文）外文翻译 are strong and abrasive, requiring 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 oxyg

17、en 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 manganese have various effects on the machinability of steels, depending on their composition. Plain low-carb

18、on 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 steels are very difficult to machine and usually require annealing prior to machining. Machinabilit

19、y 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, and vanadium, which improve the properties of steels, generally reduce machinability. The effect of boron is n

20、egligible. 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 ratio of the manganese sulfide inclusions； the higher the oxygen content, the lower the aspect ratio and the hig

21、her 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 machined part in service. At elevated temperatures, for example, lead causes embrittlement of steels (liquid-meta

22、l embrittlement, hot shortness； see Section 1.4.3), although at room temperature it has no effect 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 te

23、mperature, 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 solely to improve machinability. 2、 Machinability of Various Other Metals Aluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor surface finish. High cutting speeds, high rake