機(jī)械類英文文獻(xiàn)翻譯-預(yù)覽頁(yè)
【正文】 gh 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。 they can lead to severe reduction in the loadcarrying capacity of the ponent. Furthermore, machining of these materials requires careful removal of machining debris to avoid contact with and inhaling of the fibers. The machinability of ceramics has improved steadily with the development of nanoceramics (Section ) and with the selection of appropriate processing parameters, such as ductileregime cutting (Section ). Metalmatrix and ceramicmatrix posites can be difficult to machine, depending on the properties of the individual ponents, ., reinforcing or whiskers, as well as the matrix material. Thermally Assisted Machining Metals and alloys that are difficult to machine at room temperature can be machined more easily at elevated temperatures. In thermally assisted machining (hot machining), the source of heat—a torch, induction coil, highenergy beam (such as laser or electron beam), or plasma arc—is forces, (b) increased tool life, (c) use of inexpensive cuttingtool materials, (d) higher materialremoval rates, and (e) reduced tendency for vibration and chatter. It may be difficult to heat and maintain a uniform temperature distribution within the workpiece. Also, the original microstructure of the workpiece may be adversely affected by elevated temperatures. Most applications of hot machining are in the turning of highstrength metals and alloys, although experiments are in progress to machine ceramics such as silicon nitride. SUMMARY Machinability is usually defined in terms of surface finish, tool life, force and power requirements, and chip control. Machinability of materials depends not only on their intrinsic properties and microstructure, but also on proper selection and control of process variables. 可機(jī)加工性 一種材料的可機(jī)加工性通常以四種因素的方式定義： 分的表面光潔性和表面完整性。 以這種方式，好的可機(jī)加工性指的是好的表面光潔性和完整性，長(zhǎng)的刀具壽命，低的切削力和功率需求。盡管已不再大量的被使用，近乎準(zhǔn)確的機(jī)加工率在以下的例子中能夠被看到。 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。 鋼中的磷有兩個(gè)主要的影響。第二個(gè)影響是增加的硬度引起短切屑而不是不斷的細(xì)長(zhǎng)的切屑的形成，因此提高可加工性。因?yàn)樗牡涂辜魪?qiáng)度。除了這個(gè)作用，鉛降低第一剪切區(qū)中的剪應(yīng)力，減小切削力和功率消耗。 然而，因?yàn)殂U是有名的毒素和污染物，因此在鋼的使用中存在著嚴(yán)重的環(huán)境隱患（在鋼產(chǎn)品中每年大約有4500噸的鉛消耗）。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。振動(dòng)能成為一個(gè)問題，需要有高硬度的機(jī)床。 鋼中其它元素在可機(jī)加工性方面的影響 鋼中鋁和矽的存在總是有害的，因?yàn)檫@些元素結(jié)合氧會(huì)生成氧化鋁和矽酸鹽，而氧化鋁和矽酸鹽硬且具有磨蝕性。低碳素鋼（%的碳）通過形成一個(gè)積屑瘤能生成很差的表面光潔性。 其它合金元素，例如鎳、鉻、鉗和釩，能提高鋼的特性，減小可機(jī)加工性。越高的含氧量，就產(chǎn)生越低的縱橫比和越高的可機(jī)加工性。在室溫下，二次磷化鋼的機(jī)械性能依賴于變形的硫化錳夾雜物的定位（各向異性）。有高含量的矽的鍛鋁合金鑄鋁合金也許具有磨蝕性，它們要求更硬的刀具材料。 灰鑄鐵普遍地可加工，但也有磨蝕性。 鈷基合金有磨蝕性且高度加工硬化的。青銅比黃銅更難機(jī)加工。尖的刀具是很必要的。它生成很差的表面光潔性且刀具磨損非常大。 鋯有很好的機(jī)加工性。 塑性塑料通常有低的導(dǎo)熱性，低的彈性模數(shù)和低的軟化溫度。有了空氣流，汽霧或水溶性油，通常就能實(shí)現(xiàn)冷卻。它的機(jī)加工性和熱塑性塑料的相同。而且，這些材料的機(jī)加工要求對(duì)加工殘片仔細(xì)切除，以此來避免接觸和吸進(jìn)纖維。在熱輔助加工時(shí)（高溫切削），熱源—一個(gè)火把，感應(yīng)線圈，高能束流（例如雷射或電子束），或等離子弧—被集中在切削刀具前的一塊區(qū)域內(nèi)。（d）更高的材料切除率。盡管實(shí)驗(yàn)在進(jìn)行中，以此來機(jī)加工陶瓷器如氮化矽，但高溫切削仍大多數(shù)應(yīng)用在高強(qiáng)度金屬和高溫度合金的
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