中英文翻译机械

外文翻译

LATHES AND GRINDING

Lathes are machine tools designed primarily to do turning, facing and boring. Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathe also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the workpiece. The 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. Modern lathes date form 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 motion of the spindle and leadscrew and thus enable threads to be cut.

Lathe Construction. The essential components of a lathe 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 usually is 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 way, 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

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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 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 gear——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 modern lathes all the speeds can be obtained merely by from two to four levers. An increasing trend is to provide to continuously variable speed range through electrical or mechanical drives.

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 tapes. 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

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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 than 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 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

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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 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 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 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 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

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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 cam 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

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this gear box is driven from the lathe spindle by means of 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 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.

The common machining processes of drilling, turning, and milling generally produce a fairly large chip in comparison to those produced by the processes discussed in this section. Abrasive materials are the cutting tools in the machining processes called grinding. Grinding machines and grinding processes make up one of the most important areas in all machining.

Grinding processes are chip-making metal cutting processes just like drilling, turning, and milling. However, grinding processes remove very small chips (called swarf) in very large numbers by the cutting action of many small individual abrasive grains. These abrasive grains are formed into a grinding wheel that is rotated

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against the workpiece at high speed. Each sharp corner of a grain cuts a small bit of material from the workpiece. When the corners become dull, heat and pressure increase, fracturing grains in the grinding wheel. This ability of the grains to microfracture and expose new sharp edges is termed friability. Some abrasive grains are produced to be tough (not break down readily). These are used in harsh grinding situations, such as the rough grinding (snagging) of castings in a foundry. Other grains are produced to break down readily and are used in grinding wheels where cool grinding is essential. An example of such an application would be the grinding of hardened steels. The characteristics of the bonding material are carefully matched to the abrasive grain by the producers of abrasive products. As the bonding material that holds the grains breaks down, new sharp grains are exposed, replacing the worn ones. This also provides a method of sharpening grinding wheels. Abrasive materials are also coated on sheets of cloth or paper in the form of sandpaper or sanding belts and disks. They also appear as solid blocks such as sharpening or honing stones or deburring media such as pellets.

In machining, grinding processes are most often used as finish machining processes. The reason for this is that very small amounts (less than 0.001 in.) of material can be removed from the workpiece. This is extremely useful in finish machining a part to close dimensional accuracies. Furthermore, grinding processes result in

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very smooth surface finishes on the workpiece.

The abrasive materials that are the cutting tools in the grinding process are much harder than the equivalent materials used in common drills, laths, and milling cutters. Therefore, these materials can be used to machine much harder materials than could ever be cut with high speed steel or even carbide. The grinding process can be applied to finish machine metals that have been hardened by heat treatment. For example, bearing races may be premachined to rough dimensions before heat treating. After hardening and tempering to exact specifications, they may be finish machined by grinding.

A grinding machine is a machine which employs a grinding wheel for producing cylindrical, conical or plane surfaces accurately and economically. There is a great variety of grinding machines. The machines that are generally used are cutter grinder, surface grinder, centerless grinding, external grinder, internal grinder and tool grinder.

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车床与磨削

车床主要是为了进行车外圆、车端面和镗孔等项工作而设计的机床。车削很少在其他种类的机床上进行，而且任何一种其他机床都不能像车床那样方便地进行车削加工。由于车床还可以用来钻孔和铰孔，车床的多功能性可以使工件在一次装夹中进行几种加工。这就是在生产中普遍使用各种车床比其他种类的车床都要多的原因

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接的变速装置，这样就可以切削螺纹。

车床的主要部件有：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。通常在床身上面有内外两组平行的导轨。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装在导轨上并（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

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遭到破坏。大多数现代车床的导轨要进行表面淬火处理，以减小磨损和擦伤，具有更大的耐磨性。

主轴箱安装在床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。它基本上由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，主轴可以在许多中转速下旋转。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，就能得到全部挡位的转速。目前发展的趋势是通过电气的或机械的装置进行无级变速。

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送料时，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。而小型的车床常带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。

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有5~15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，并可以在导轨上做纵向移动，底座上有一个可以使整个尾座组

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件夹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。锁定位置可以使套筒在所需要的位置上夹紧。

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是其前后移动。

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。手动的另一端与溜板箱背面的小齿轮连接，小齿轮和齿条啮合，齿条倒装在床身前边缘的下面。

利用光杠可以将动力传递给大拖板和横拖板。光杠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

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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一个锥齿啮合，为大拖板提供“向前”或“向后”的动力。适当的离合器或者与齿条小齿轮连接或者与横拖板的螺杆连接，使拖板纵向移动或使拖板横向移动。

对于螺纹加工，丝杠提供了第二种纵向移动方法。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溜板箱与丝杠之间的直接机械连接来实现的，对开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。

现代车床有一个变速齿轮箱，齿轮箱的输入端由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动变速齿轮箱，再带动丝杠和光杠，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0.008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。一些老式的或廉价的车床为了能够得到所有的进给量和加工出所有的螺纹，必须更换主轴和变速齿轮箱之间的齿轮系中的一个或两个齿轮。

与本节讨论的磨削相比，常用的钻削、车削和铣削产生的切屑一般都比教大。在称为磨削的机加工方法之中，研磨材料就是切削刀具。磨床和磨削方法是所有机加工中最重要的领域之一。

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像钻削、车削和铣削一样，磨削也是产生切屑的金属切削方法。但磨削也是通过许许多多小的独立磨粒的切削动作，来切除大量的细小切屑的。将这些磨粒制成砂轮，以高速相对于工件旋转，磨粒的每个锐角从工件上切除一小点材料。当磨粒锐角变钝后，切削是的热量和压力就增加，使砂轮中的磨粒断裂。磨粒显微断裂和露出新的锐角的能力，称为自锐性。某些磨粒具有韧性（不易破裂），它们用于像铸件的粗磨（清除铸件毛刺、浇口等）这类粗糙磨削的场合。另一类容易磨断的磨粒做的砂轮，主要用于冷磨削。淬硬钢的磨削就是这种用途中的一个例子。对研磨产品的生产者来说，粘结材料的特性应与磨粒仔细的匹配。将磨粒结合在一起的粘结材料破裂时，显露出新的尖锐的磨粒，以代替磨钝了的磨粒。这也为砂轮的锋利提供了一种方法。可以将研磨材料涂在布或纸上，形成砂纸、砂带和砂盘。也可将研磨材料做成磨块，如磨刀石或珩磨石，以及用作去毛刺的喷丸。

磨削是机加工中最常用的精加工方法，原因是它能从工件上切除极小量的材料（<0.001英寸）。这对将零件精加工到高的尺寸精度，是及其有用的。再者，磨削能使工件表面光洁度。

在磨削过程中，作为切削刀具的磨削材料，比制造普通钻头、车刀和铣刀的材料要硬得多。因此，它可以用来加工比高速钢甚至硬质合金所能切削的材料硬得多的材料。磨削可用来精加工已热处理淬硬了的金属。例如，轴承圈可在热处理前粗加工，淬火和回火后，用磨削进行精加工。

磨床是使用砂轮精确经济地加工圆柱面、圆锥面和平面的

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机器。磨床有许多种类，常用的磨床有刀具磨床、平面磨床、无心磨床、外圆磨床、内心磨床及工具磨床等。

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