外文翻译--金属切削刀具

1 LATHES The basic machines that are designed primarily to do turning, facing and boring are called lathes. Very little turning is done on other types of machine tools, and nine can do it with equal facility. Because lathe can do boring, facing, drilling, and reaming in addition to turning, their versatility permits several operations to be performed with a single setup of the workpiece. This accounts for the fact that lathes of various types are more widely used in manufacturing than any other machine tool. Lathes in various forms have existed for more than two thousand years. Modem lathes date from about 1797, when Henry Maudsley developed one with a leadscrew. It provided controlled, mechanical feed of the tool. This ingenious Englishman also developed a change-gear system that could connect the motions of the spindle and leadscrew and thus enable threads to be cut. Lathe Construction. The essential components of a lathe are depicted in the block diagram of Fig.15-1.These are the bed, headstock assembly, tailstock assembly, carriage assembly, quick-change gear box, and the leadscrew and feed rod. The bed is the backbone of a lathe. It is usually made of well-normalized or aged gray or nodular cast iron and provides a heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, are contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat way in one or both sets. Because several other components are mounted and/or move on the ways they must be made with precision to assure accuracy of alignment. Similarly, proper precaution should be taken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed. The ways on most modern lathes are surface hardened to offer greater resistance to wear and abrasion. The headstock is mounted in a fixed position on the inner ways at one end of the lathe bed. It provides a powered means of rotating the work at various speeds. It consists, essentially, of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmission-through which the spindle can be rotated at a number of speeds. Most lathes provide from eight to eighteen speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives. 2 Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball types. A longitudinal hole extends through the spindle so that long bar stock can be fed through it. The size of this hole is an important size dimension of a lathe because it determines the maximum size of bar stock that can be machined when the material must be fed through the spindle. The inner end of the spindle protrudes from the gear box and contains a means for mounting various types of chucks, face plates, and dog plates on it. Whereas small lathes often employ a threaded section to which the chucks are screwed, most large lathes utilize either cam-lock or key-drive taper noses. These provide a large-diameter taper that assures the accurate alignment of the chuck, and a mechanism that permits the chuck or face plate to be locked or unlocked in position without the necessity of having to rotate these heavy attachments. Power is supplied to the spindle by means of an electric motor through a V-belt or silent-chain drive. Most modern lathes have motors of from 5 to 15 horsepower to provide adequate power for carbide and ceramic tools at their high cutting speeds. The tailstock assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clamping the entire assembly in any desired location. An upper casting fits on the lower one and can be moved transversely upon it on some type of keyed ways. This transverse motion permits aligning the tailstock and headstock spindles and provides a method of turning tapers. The third major component of the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 2 to 3 inches in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a handwheel and screw. The open end of the quill hole terminates in a Morse taper in which a lathe center, or various tools such as drills, can be held. A graduated scale, several inches in length, usually is engraved on the outside of the quill to aid in controlling its motion in and out of the upper casting. A locking device permits clamping the quill in any desired position. The carriage assembly provides the means for mounting and moving cutting tools. The carriage is a relatively flat H-shaped casting that rests and moves on the outer set of ways on the bed. The transverse bar of the carriage contains ways on which the cross slide is mounted and can be moved by means of a feed screw that is controlled by a small handwheel and a graduated dial. Through the cross slide a 3 means is provided for moving the lathe tool in the direction normal to the axis of rotation of the work. On most lathes the tool post actually is mounted on a compound rest. This consists of a base, which is mounted on the cross slide so that it can be pivoted about a vertical axis, and an upper casting. The upper casting is mounted on ways on this base so that it can be moved back and forth and controlled by means of a short lead screw operated by a handwheel and a calibrated dial. Manual and powered motion for the carriage, and powered motion for the cross slide, is provided by mechanisms within the apron, attached to the front of the carriage. Manual movement of the carriage along the bed is effected by turning a handwheel on the front of the apron, which is geared to a pinion on the back side. This pinion engages a rack that is attached beneath the upper front edge of the bed in an inverted position. To impart powered movement to the carriage and cross slide, a rotating feed rod is provided. The feed rod, which contains a keyway throughout most of its length, passes through the two reversing bevel pinions and is keyed to them. Either pinion can be brought into mesh with a mating bevel gear by means of the reversing lever on the front of the apron and thus provide “forward” or “reverse” power to the carriage. Suitable clutches connect either the rack pinion or the cross-slide screw to provide longitudinal motion of the carriage or transverse motion of cross slide. For cutting threads, a second means of longitudinal drive is provided by a lead screw. Whereas motion of the carriage when driven by the feed-rod mechanism takes place through a friction clutch in which slippage is possible, motion through the lead screw is by a direct, mechanical connection between the apron and the lead screw. This is achieved by a split nut. By means of a clamping lever on the front of the apron, the split nut can be closed around the lead screw. With the split nut closed, the carriage is moved along the lead screw by direct drive without possibility of slippage. Modern lathes have a quick-change gear box. The input end of this gear box is driven from the lathe spindle by means of suitable gearing. The output end of the gear box is connected to the feed rod and lead screw. Thus, through this gear train, leading from the spindle to the quick-change gear box, thence to the lead screw and feed rod, and then to the carriage, the cutting tool can be made to move a specific distance, either longitudinally or transversely, for each revolution of the spindle. A typical lathe provides, through the feed rod, forty-eight feeds ranging from 0.002 inch to 0.118 4 inch per revolution of the spindle, and, through the lead screw, leads for cutting forty-eight different threads from 1.5 to 92 per inch. On some older and some cheaper lathes, one or two gears in the gear train between the spindle and the change gear box must be changed in order to obtain a full range of threads and feeds. CUTTING TOOL Shape of cutting tools, particularly the angles, and tool material are very important factors. The purpose of this unit is to introduce the cutting tool geometry and tool materials. Cutting Tool Geometry Angles determine greatly not only tool life but finish quality as well. General principles upon which cutting tool angles are based do not depend on the particular tool. Basically, grinding wheel are being designed. Since, however, the lathe (turning) tool, depicted in Fig.14-1, might be easiest to visualize, its geometry is discussed. Tool features have been identified by many names. The technical literature is full of confusing terminology. Thus in the attempt to clear up existing disorganized conceptions and nomenclature, the American Society of Mechanical Engineers published ASA Standard B5-22-1950. what follows is based on it. A single-point tool is a cutting tool having one face and one continuous cutting edge. Tool angles identified in Fig. 14-2 are as follows: (1) Back-rake angle, (2) Side-rake angle, (3) End-relief angle (4) End-relief angle (5) Side-relief angle (6) End-cutting-edge angle, (7) Side-cutting-edge angle, (8) Nose angle, (9) Nose radius. Tool angle 1, on front view, is the back-rake angle. It is the angle between the tool face and a line parallel to the base of the shank in a longitudinal plane perpendicular to the tool base. Then this angle is downward from front to rear of the cutting edge, the rake id positive； when upward from front to back, the rake is negative. This angle is most significant in the machining process, because it directly affects the cutting force, finish, and tool life. The side-rake angle, numbered 2, measures the slope of the face in a cross plane perpendicular to the tool base. It, also, is an important angle, because it directs chip flow to the side of the tool post and permits the tool to feed more easily into the work. The end-relief angle is measured between a line perpendicular to the base and the end flank immediately below the end cutting edge； it is numbered 3 in the figure. It provides clearance between work and tool so that its cut surface can flow by with minimum rubbing against the tool. To save time, a portion of the end flank of the tool 5 may sometimes be left unground, having been previously forged to size. In such case, this end-clearance angle, numbered 4, measured to the end flank surface below the ground portion, would be larger than the relief angle. Often the end cutting edge is oblique to the flank. The relief angle is then best measured in a plane normal to the end cutting edge perpendicular to the base of the tool. This clearance permits the tool to advance more smoothly into the work. The side-relief angle, indicated as 5, is measured between the side flank, just below the cutting edge, and a line through the cutting edge perpendicular to the base of the tool. This clearance permits the tool to advance more smoothly into the work. Angle 6 is the end-cutting-edge angle measured between the end cutting edge and a line perpendicular to the side of the tool shank. This angle prevents rubbing of the cut surface and permits longer tool life. The side-cutting-edge angle, numbered 7, is the angle between the side cutting edge and the side of the tool shank. The true length of cut is along this edge. Thus the angle determines the distribution of the cutting force. The greater the angle, the longer the tool life； but the possibility of chatter increases. A compromise must, as usual, be reached. The nose angle, number 8, is the angle between the two component cutting edges. If the corner is rounded off, the arc size is defined by the nose radius 9. the radius size influences finish and chatter. Cutting Tool Materials A large number of cutting tool materials have been developed to meet the demands of high metal-removal rates. The most important of these materials and their influence on cutter design, are described below. High Carbon Steel. Historically, high carbon steel was the earliest cutting material used industrially, but it has now been almost entirely superseded since it starts to temper at about 220 and this irreversible softening process continues as temperature increases. Cutting speeds with carbon steel tools are therefore limited to about 0.15m/s (30ft/min) when cutting mild steel, and even at these speeds a copious supply of coolant is required. High-speed Steel. To overcome the low cutting speed restriction imposed by plain carbon steels, a range of alloy steels, known as high-speed steels, began to be introduced during the early years of this century. The chemical composition of these steels varies greatly, but they basically contain about 0.7% carbon and 4% chromium, 6 with addition of tungsten, vanadium, molybdenum and cobalt in varying percentages. They maintain their hardness at temperatures up to about 600 , but soften rapidly at cutting speeds in excess of 1.8m/s (350ft/min), and many cannot successfully cut mild steel faster than 0.75m/s (150ft/min). Sintered Carbides. Carbide cutting tools, which were developed in Germany in the late 1920s, usually consist of tungsten carbide or mixtures of tungsten carbide and titanium or tantalum carbide in powder form, sintered in a matrix of cobalt or nickel. Because of the comparatively high cost of this tool material and its low rupture strength, it is normally produced in the form of tips which are either brazed to a steel shank or mechanically clamped in a specially designed holder. Mechanically clamped tool tips are frequently made as throwaway inserts. When all the cutting edges have been used the inserts are discarded, ad regrinding would cost more than a new tip. The high hardness of carbide tools at elevated temperatures enables them to be used at much faster cutting speeds than high-speed steel (of 3-4m/s（ 600-800ft/min）when cutting mild steel). They are manufactured in several grades, enabling them to be used for most machining applications. Their earlier brittleness has been largely overcome by the introduction of tougher grades, which are frequently used for interrupted cuts including many arduous face-milling operations. Recently, improvements have been claimed by using tungsten carbide tools coated with titanium carbide or titanium nitride (about 0.0005mm coating thickness). These tools are more resistant to wear than conventional tungsten carbide tools, and the reduction in interface friction using titanium nitride results in a reduction in cutting forces and in tool temperatures. Hence, higher metal removal rates are possible without detriment to tool life or alternatively longer tool lives could be achieved at unchanged metal removal rates. The uses of other forms of coating with aluminum oxide and polycrystalline cubic boron nitride are still in an experimental stage, but it is likely that they will have important applications when machining cast iron, hardened steels and high melting point alloys. Ceramics. The so-called ceramic group of cutting tools represents the most recent development in cutting tool materials. They consist mainly of sintered oxides, usually aluminum oxide, and are almost invariably in the form of clamped tips. Because of the comparative cheapness of ceramic tips and the difficulty of grinding them without causing thermal cracking, they are made as throw-away inserts. 7 Ceramic tools are a post-war introduction and are mot yet in general factory use. Their most likely application is in cutting metal at very high speeds, beyond the limits possible with carbide tools. Cramics resist the formation of a built-up edge and in consequence produce good surface finishes. Since the present generation of machine tools is designed with only sufficient power to exploit carbide tooling, it is likely that, for the time being, ceramics will be restricted to high-speed finish machining where is sufficient power available for the light cuts taken. The extreme brittleness of ceramic tools has largely limited their use to continuous cuts, although their use in milling is now possible. As they are poorer conductors of heat than carbides, temperatures at the rake face are higher than in carbide tools, although the friction force is usually lower. To strengthen the cutting edge, and consequently improve the life of the ceramic tool, a small chamfer or radius is often stoned on the cutting edge, although this increases the power consumption. Diamonds. For producing very fine finishes of 0.05-0.08um（ 2-3um) on non-ferrous metals such as copper and aluminum, diamond tools are often used. The diamond is brazed to a steel shank. Diamond turning and boring are essentially finishing operations, as the forces imposed by any but the smallest cuts cause the diamond to fracture or be torn from its mounting. Under suitable conditions diamonds have exceptionally long cutting lives. Synthetic polycrystalline diamonds are now available as mechanically clamped cutting tips. Due to their high cost they have very limited applications, but are sometimes used for machining abrasive aluminum-silicon alloys, fused silica and reinforced plastics. The random orientation of their crystals gives them improved impact resistance, making them suitable for interrupted cutting. 8 车床 用于车外圆、端面和镗孔等加工的机床称作车床。车削很少在其他种类的机床上进行，因为其他机床都不能像车床那样方便地进行车削加工。由于车床除了用于车外圆还能用于镗孔、车端面、钻孔和铰孔，车床的多功能性可以是共建在一次定位安装中完成多种加工。这种是在生产中普遍使用的各种车床比其他种类的机床都要多的原因。 两千多年前就已经有了车床。现代车床可以追溯到大约 1797 年，那时亨利莫德斯利发明了一种具有丝杠的车床。这种车床可以控制工具的机械进给。这位聪明的英国人还发明了一种把主轴和丝杠相连的变速装置，这样就可以切削螺纹。 图 15-1 中标出了车床的主要部件：床身、主轴箱组件、尾架组件、拖板组件、变速齿轮箱、丝杠和光杠。 床身是车床的基础件。它通常是由经过充分正火或时效处理的灰铸铁或者球墨铸铁制成，它是一个坚固的刚性框架，所有其他主要部件都安装在床身上。通常在床身上那个面有内外另组平行的导轨。一些制造厂生产的四个条导轨都采用倒“ V”形，而另一些制造厂则将倒“ V”形导轨和平 面导轨相结合。由于其他的部件要安置在导轨上并（或）在导轨上移动，导轨要经过精密加工，以保证其装配精度。同样地，在操作中应该小心，以避免损伤导轨。导轨上的任何误差，常常会使整个机床的精度遭到破坏。大多数现代车床的导轨要进行变面淬火处理，以减少磨损和擦伤，具有更大的耐磨性。 主轴箱安装在车身一端内导轨的固定位置上。它提供动力，使工件在各种速度下旋转。它基本上有一个安装在精密轴承中的空心主轴和一系列变速齿轮 类似于卡车变速箱所组成，通过变速齿轮，主轴可以在许多种转速下旋转。大多数车床有 8 18 种转速，一般按等比 级数排列。在现代车床上只需扳动 2 4 个手柄，就能得到全部档位的转速。目前发展的趋势是通过电气的或机械的装置进行无极变速。 由于车床的精度在很大程度上取决于主轴，因此主轴的结构尺寸较大，通常安装在紧密配合的重型圆锥滚子轴承或球轴承中。主轴中有一个贯穿全长的通孔，长棒料可以通过该孔送料。主轴孔的大小是车床的一个重要尺寸，因为当工件必须通过主轴孔供料时，它确定了能够加工棒料毛坯的最大外径尺寸。 主轴的内端从主轴箱中凸出，其上可以安装多种卡盘、花盘和挡块。而小型的车床常有螺纹截面供安装卡盘之用。很多大车床使用偏心夹 或键动圆锥轴头。这些附件组成了一个大直径的圆锥体，以保证对卡盘进行精确地装配，并且不用旋转这些笨重的附件就可以锁定或松开卡盘或花盘。 9 主轴由电动机经 V 带或无声链装置提供动力。大多数现代车床都装置有 515 马力的电动机，为硬质合金和金属陶瓷合金刀具提供足够的动力，进行高速切削。 尾座组件主要由三部分组成。底座与床身的内侧导轨配合，并可以子导轨上做纵向移动，底座上有一个可以使整个尾座组件加紧在任意位置上的装置。尾座安装在底座上，可以沿键槽在底座上横向移动，使尾座与主轴箱中的主轴对中并为切削圆锥体提供方便。尾座组 件的第三部分是尾座套筒，它是一个直径通常在2 3 英寸之间的钢制空心圆柱轴。通过手轮和螺杆，尾座套筒可以在尾座体中纵向移入和移出几英寸。活动套筒的开口一端具有莫氏锥度，可以用于安装顶尖或诸如钻头之类的各种刀具。通常在活动套筒的外表面刻有几英寸长的刻度，以控制尾座的前后移动。锁定装置可以使套筒在所需的位置上夹紧。 拖板组件用于安装和移动切削工具。拖板是一个相对平滑的 H 形铸件，安装在床身外侧导轨上，并可以在上面移动。大拖板上有横向导轨，使横向拖板可以安装在上面，并通过丝杠使其运动，丝杠由一个小手柄和刻度盘控制。横 拖板可以带动刀具垂直于工件的旋转轴线切削。 大多数车床的刀架安装在复式刀座上，刀座上有底座，底座安装在横拖板上，可绕垂直轴和上刀架转动。上刀架安装在底座上，可用手轮和刻度盘控制一个短丝杠使其前后移动。 溜板箱装在大拖板前面，通过溜板箱内的机械装置可以手动和动力驱动大拖板以及动力驱动横拖板。通过转动溜板箱前的手轮，可以手动操作拖板沿床身移动。手轮的另一端与溜板箱背面的小齿轮连接，小齿轮与齿条啮合，齿条倒装在床身前上边缘的下面。 利用光杆可以将动力传递给大拖板和横拖板。光杆上有一个几乎贯穿于整个光杠的键槽，光杠通过两个转向相反并用键连接的锥齿轮传递动力。通过溜板箱前的换向手柄可使啮合齿轮与其中的一个锥齿轮啮合，为大拖板提供“向前”或“向后”的动力。适当的离合器或者齿条小齿轮连接或者与横拖板的螺杆连接，是拖板纵向移动或使横拖板横向移动。 对于螺纹加工，丝杠提供了第二种纵向移动的方法。光杠通过摩擦离合器驱动拖板移动，离合器可能会产生打滑现象。而丝杠产生的运动是通过滑板箱与丝杠之间的直接机械连接来实现的，对于螺母可以实现这种连接。通过溜板 箱前面的夹紧手柄可以使对开螺母紧紧包合丝杠。当对开螺母闭合时，可以沿丝杠直接驱动拖板，而不会出现打滑的可能性。 现代车床有一个变速齿轮箱，齿轮箱的输入端有车床主轴通过合适的齿轮传动来驱动。齿轮箱的输出端与光杠和丝杠连接。主轴就是这样通过齿轮传动链驱 10 动变速齿轮箱，在带动丝杠和光杠，然后带动拖板，刀具就可以按主轴的转数纵向地或横向地精确移动。一台典型的车床的主轴每旋转一圈，通过光杠可以获得从 0.002 到 0.118 英寸尺寸范围内的 48 种进给量；而使用丝杠可以车削从 1.5 到92 牙 /英寸范围内的 48 种不同螺纹。一些老 式的或价廉的车床为了能够得到所有的进给量和加工出多有螺纹，必须更换主轴和变速箱之间的齿轮系中的一个或两个齿轮。 金属切削刀具 刀具的形状（特别是其角度）和材料是刀具的两个非常重要的因素。本文向大家介绍刀具的几何参数和刀具材料。 刀具几何参数 刀具的角度不仅在很大程度决定了刀具的寿命，而且也决定加工的表面质量。刀具角度设计的一般性原则不因某种特殊刀具而变。车刀、铣刀、钻头甚至是砂轮的设计，所要考虑的因素基本相同。图 14.1 所示的车刀外形易于观察，我们即以此为例来讨论刀具的几何参数。 刀具特征参数名目繁多，技术 文献中术语使用也很混乱。为了澄清已有的混乱的概念和术语，美国机械工程师协会颁布了 ASA 标准 B5