【導讀】是真空電子管，雖然轉(zhuǎn)速高，但傳遞的功率小、轉(zhuǎn)矩也小。隨著高速切削的發(fā)展的需要和功。大轉(zhuǎn)矩、高轉(zhuǎn)速的高速機床電主軸。切削技術是加工制造技術的一次革命性突破，是未來竊謔加工技術的重點發(fā)展方向。效率、加工質(zhì)量和加工精度大幅度提升的先進制造技術。法承受，切削加工不可能進行，而處于v2以上切削速度的加工，就是高速切削加工。上升趨勢，而后急劇下降，這說明高速切削比常規(guī)切削輕快，兩者的機理也不同。在高速切削時，切削的切除產(chǎn)生在極端的瞬。所以高速切削不僅可以大大減少加工工序，提高加工效率，而且可以用于精密件。因高速切削具有以上有別于普通切削的特點，所以高速切削已經(jīng)當前機床領域的熱點。軸的結構形式和性能將直接決定機床的性能，因此研究電主軸系統(tǒng)非常有意義。一系列支持電主軸運轉(zhuǎn)的外圍設備，具體結構如圖。

　　

【正文】 r 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 24 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. Zirconium has good machinability. It requires a coolanttype cutting fluid, however, because of the explosion and fire. 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 proper support of the workpiece. Tools should be sharp. External cooling of the cutting zone may be necessary to keep the chips from being “gummy” and sticking to the tools. Cooling can usually be achieved with a jet of air, vapor mist, or watersoluble oils. Residual stresses may develop during machining. To relieve these stresses, machined parts can be annealed for a period of time at temperatures ranging from C?80 to C?160 ( F?175 to F?315 ), and then cooled slowly and uniformly to room temperature. Thermosetting plastics are brittle and sensitive to thermal gradients during cutting. Their machinability is generally similar to that of thermoplastics. Because of the fibers present, reinforced plastics are very abrasive and are difficult to machine. Fiber tearing, pulling, and edge delamination are significant problems。 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 ). 25 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. 譯文 ： 可機加工性 一種材料的可機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。 刀具的壽命。 切削力和功率的需求。 切屑控制。 以這種方式，好的可機加工性指的是好的表面光潔性和完整性，長的刀具壽命，低的切削力和功率需求。關于切屑控制，細長的卷曲切屑，如果沒有被切割成小片，以在切屑區(qū)變的混亂，纏在一起的方式能夠嚴重的介入剪切工序。 因為剪切工序的復雜屬性，所以很難建立定量地釋義材料的可機加工性 的關系。在制造廠里，刀具壽命和表面粗糙度通常被認為是可機加工性中最重要的因素。盡管已不再大量的被使用，近乎準確的機加工率在以下的例子中能夠被看到。 26 鋼的可機加工性 因為鋼是最重要的工程材料之一（正如第 5 章所示），所以他們的可機加工性已經(jīng)被廣泛地研究過。通過宗教鉛和硫磺，鋼的可機加工性已經(jīng)大大地提高了。從而得到了所謂的易切削鋼。 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)引起應力。其結果是使切屑容易斷開而變小，從而改善了可加工性。這些夾雜物的大小、 形狀、分布和集中程度顯著的影響可加工性?；瘜W元素如碲和硒，其化學性質(zhì)與硫類似，在二次硫化鋼中起夾雜物改性作用。 鋼中的磷有兩個主要的影響。它加強鐵素體，增加硬度。越硬的鋼，形成更好的切屑形成和表面光潔性。需要注意的是軟鋼不適合用于有積屑瘤形成和很差的表面光潔性的機器。第二個影響是增加的硬度引起短切屑而不是不斷的細長的切屑的形成，因此提高可加工性。 含鉛的鋼 鋼中高含量的鉛在硫化錳夾雜物尖端析出。在非二次硫化鋼中，鉛呈細小而分散的顆粒。鉛在鐵、銅、鋁和它們的合金中是不能溶解的。因為它的低抗剪強度。因此，鉛 充當固體潤滑劑并且在切削時，被涂在刀具和切屑的接口處。這一特性已經(jīng)被在機加工鉛鋼時，在切屑的刀具面表面有高濃度的鉛的存在所證實。 當溫度足夠高時 — 例如，在高的切削速度和進刀速度下 — 鉛在刀具前直接熔化，并且充當液體潤滑劑。除了這個作用，鉛降低第一剪切區(qū)中的剪應力，減小切削力和功率消耗。鉛能用于各種鋼號，例如 10XX， 11XX， 12XX， 41XX 等等。鉛鋼被第二和第三數(shù)碼中的字母 L 所識別（例如， 10L45）。（需要注意的是在不銹鋼中，字母 L的相同用法指的是低碳，提高它們的耐蝕性的條件）。 然而，因為鉛是有名的毒 素和污染物，因此在鋼的使用