机械设计专业外文文献翻译

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1、 本科毕业设计（论文） 外文译文 院 （系）： 机电工程学院 专 业： 机械设计制造及其自动化 姓 名： 学 号： 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 Technology Machining 机械工业出版社 2004 年 3 月第 1 版 页 564560P 美 s. 卡尔帕基安 (Serope kalpakjian) s.r 施密德 (Steven R.Schmid) 著 原文 ： 20.9 MACHINABILITY The machinability of a mat

2、erial 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 for chip

3、 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 machinability o

4、f 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. 20.9.1 Machinability Of Steels Because steels are

5、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 Rephosphorized steels. Sulfur in steels

6、 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 inclusions significantly influenc

7、e 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

8、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 machinability. Leaded Steels. A high per

9、centage 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

10、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 the temperature is sufficiently high-for instance, at high cutting sp

11、eeds 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, 12

12、xx, 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 corrosion resistance.) However, because lead is a well-known toxin a

13、nd 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 use of lead in steels (lead-free steels). Bismuth and tin are now bei

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