ca6140车床的数控机械外文翻译-数控设计(编辑修改稿)

ca6140车床的数控机械外文翻译-数控设计(编辑修改稿)内容摘要：

an 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 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 4 form a builtup edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are remended. 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 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 reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials. Cobaltbased alloys are abrasive and highly workhardening. They require sharp, abrasionresistant tool materials and low feeds and speeds. Wrought copper can be difficult to machine because of builtup edge formation, although cast copper alloys are easy to machine. Brasses are easy to machine, especially with the addition pf lead (leaded freemachining brass). Bronzes are more difficult to machine than brass. Magnesium is very 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 workhardening, so it can produce poor surface finish. Sharp tools are necessary. Nickelbased alloys are workhardening, abrasive, and strong at high temperatures. Their machinability is similar to that of stainless steels. Tantalum is very workhardening, ductile, and soft. It produces a poor surface finish。 tool wear is high. Titanium and its alloys have poor thermal conductivity (indeed, the lowest of all metals), causing significant temperature rise and builtup 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. 5 Zirconium has good machinability. It requires a coolanttype cutting fluid, however, because of the explosion and fire. 3. Machinability of Various Materials Graphite is abrasive。 it requires hard, abrasionresistant, sharp tools. Thermoplastics generally have low thermal conductivity, low elastic modulus, and low softening temperature. Consequently, 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。