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1、word本科毕业设计论文英语译文院 系： 某某理工大学轻工学院 专 业： 机械设计制造与其自动化 姓 名： X 卫 学 号 200515160212 指导教师评语： 签名： 年 月 日外语文献翻译摘自: 制造工程与技术机加工英文版 Manufacturing Engineering and TechnologyMachining机械工业 2004年3月第1版美 s. 卡尔帕基安(Serope kalpakjian) s.r 施密德(Steven R.Schmid) 著原文：20.9 MACHINABILITYThe machinability of a material usually def
2、ined 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 for chip control, long and th
3、in (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by being entangled in the cutting zone.Because of the plex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinability of a material. In manufacturi
4、ng 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.20.9.1 Machinability Of SteelsBecause steels are among the most important engin
5、eering 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 forms manganese sulfide inclus
6、ions (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 machinability. Elements such
7、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 surface finish. Note that so
8、ft 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 percentage of lead in steels solidif
9、ies 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 lubricant (Section 32.11) and is
10、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 and feeds (Section 20.6)the l
11、ead 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, 41xx, etc. Leaded steels are i
12、dentified 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 pollutant, there are serious en
13、vironmental 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 investigated as possible substitu
14、tes 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 and wear. Temperature is corre
15、spondingly 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. 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 resistance. Precipitation-hardening stainless steels are strong and abrasive, requiring hard and ab
