外文翻译--车床切削加工

外文翻译--车床切削加工 译文: 车床及其切削加工 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安装中完成几种加工。因此，在生产中使用的各种车床比任何其他种类的机床都多。 车床的基本部件有:床身、主轴箱组件、尾架组件、溜板组件、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，所有其他基本部件都安装在床身上。通常在床身上有内外两组平行的导轨。有些制造厂对全部四条导轨都采用导轨尖顶朝上的三角形导轨 即山形导轨 ，而有的制造厂则在一组中或者两组中都采用一个三角形导轨和一个矩形导轨。导轨要经过精密加工，以保证其直线度精度。为了抵抗磨损和擦伤，大多数现代机床的导轨是经过面淬硬的，但是在操作时还应该小心，以避免损伤导轨。导轨上的任何误差，常常意味着整个机床的精度遭到破坏。 主轴箱安装在内侧导轨的固定位置上，一般在床身的左端。它提供动力，并可使工件在各种速度下回转。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――类似于卡车变速箱一所组成。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。而且在现代机床上只需扳动2-4个手柄，就能得到全部转速。一种正在不断增长的趋势是通过电气的或者机械的装置进行无级变速。 由于机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，通常安装在预紧后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，它确定了能够加工的棒料毛坯的最大尺寸。 尾架组件主要由三部分组成。底板与床身的内侧导轨配合，并可以在导轨上做纵向移动。底板上有一个可以使整个尾架组件夹紧在任意位置上的装置。尾架体安装在底板上，可以沿某种类型的键槽在底板上横向移动，使尾架能与主轴箱中的主轴对正。尾架的第三个组成部分是尾架套筒。它是一个直径通常大约在51―76mm 2-3英寸 之间的钢制空心圆柱体。通过手轮和螺杆，尾架套筒可以在尾架体中纵向移人和移出几英寸。 车床的规格用两个尺寸表示。第一个称为车床床面上最大加工直径。这是在车床上能够旋转的工件的最大直径。它大约是两顶尖连线与导轨上最近点之间距离的两倍。第二个规格尺寸是两顶尖之间的最大距离。车床床面上最大加工直径表示在车床上能够车削的最大工件直径，而两顶尖之间的最大距离则表示在两个顶尖之间能够安装的工件的最大长度。 普通车床是生产中最经常使用的车床种类。它们是具有前面所叙述的所有那些部件的重载机床，并且除了小刀架之外，全部刀具的运动都有机动进给。它们的规格通常是:车床床面上最大加工直径为305-610mm 12-24英寸 ;两顶尖之间距离为610―1 219mm 24-48英寸 。但是，床面上最大加工直径达到1 270mm 50英寸 和两顶尖之间距离达到3 658mm 12英尺 的车床也并不少见。这些车床大部分都有切屑盘和一个安装在内部的冷却液循环系统。小型的普通车床――车床床面最大加工直径一般不超过330mm 13英寸 ――被设计成台式车床，其床身安装在工作台或柜子上。 虽然普通车床有很多用途，是很有用的机床，但是更换和调整刀具以及测量工件花费很多时间，所以它们不适合在大量生产中应用。通常，它们的实际加工时间少于其总加工时间的30,。此外，需要技术熟练的工人来操作普通车床，这种工人的工资高而且很难雇到。然而，操作工人的大部分时间却花费在简单的重复调整和观察切屑产生过程上。因此，为了减少或者完全不雇用这类熟练工人，六角车床、螺纹加工车床和其他类型的半自动和自动车床已经很好地研制出来，并已经在生产中得到广泛应用。 普通车床作为最早的金属切削机床中的一种，目前仍然有许多有用的和为人们所需要的特性。现在，这些机床主要用在规模较小的工厂中，进行小批量的生产，而不是进行大批量的生产。 在现代的生产车间中，普通车床已经被种类繁多的自动车床所取代，诸如自动仿形车床，六角车床和自动螺丝车床。现在，设计人员已经熟知先利用单刃刀具去除大量的金属余量，然后利用成型刀具获得表面光洁度和精度这种加工方法的优点。这种加工方法的生产速度与现在工厂中使用的最快的加工设备的速度相等。 普通车床的加工偏差主要依赖于操作者的技术熟练程度。设计师应该认真地确定由熟练工人在普通车床上加工的试验零件的公差。在把试验零件重新设计为生产零件时，应该选用经济的公差。 对生产加工设备来说，目前比过去更着重评价其是否具有精确的和快速的重复加工能力。应用这个来评价具体的加工方法，六角车床可以获得较高的质量评定。 在为小批量的零件 100―200件 设计加工方法时，采用六角车床是最经济的。为了在六角车床上获得尽可能小的公差值，设计人员应该尽量将加工工序的数目减至最少。 自动螺丝车床通常被分为以下几种类型:单轴自动、多轴自动和自动夹紧车床。自动螺丝车床最初是被用来对螺钉和类似的带有螺纹的零件进行自动化和快速加工的。但是，这种车床的用途早就超过了这个狭窄的范围。现在，它在许多种类的精密零件的大批量生产中起着重要的作用。工件的数量对采用自动螺丝车床所加工的零件的经济性有较大的影响。如果工件的数量少于1 000件，在六角车床上进行加工比在自动螺丝车床上加工要经济得多。如果计算出最小经济批量，并且针对工件批量正确地选择机床，就会降低零件的加工成本。 因为零件的表面粗糙度在很大程度上取决于工件材料、刀具、进给量和切削速度，采用自动仿形车床加工所得到的最小公差不一定是最经济的公差。 在某些情况下，在连续生产过程中，只进行一次切削加工时的公差可以达到?0(05mm。对于某些零件，槽宽的公差可以达到?0(125mm。镗孔和采用单刃刀具进行精加工时，公差可达到?0(0125mm。在希望获得最大产量的大批量生产中，进行直径和长度的车削时的最小公差值为土0(125mm是经济的。 金属切削加工在制造业中得到了广泛的应用。其特点是工件在加工前具有足够大的尺寸，可以将工件最终的几何形状尺寸包容在里面。不需要的材料以切屑、颗粒等形式被去除掉。去除切屑是获得所要求的工件几何形状，尺寸公差和表面 质量的必要手段。切屑量多少不一，可能占加工前工件体积的百分之几到70,―80,不等。 由于在金属切削加工中，材料的利用率相当低，加之预测到材料和能源的短缺以及成本的增加，最近十年来，金属成形加工的应用越来越多。然而，由于金属成形加工的模具成本和设备成本仍然很高，因此尽管金属切削加工的材料消耗较高，在许多情况下，它们仍然是最经济的。由此可以预料，在最近几年内，金属切削加工在制造业中仍将占有重要的位置。而且，金属切削加工的自动生产系统的发展要比金属成形加工的自动生产系统的发展要快得多。 在金属切削加工中，信息的传递是通过刚性传递介质 刀具 实现的。刀具相对工件运动，机械能通过刀具作用于工件。因此，刀具的几何形状和刀具与工件的运动方式决定了工件的最终形状。这个基本过程是机械过程:实际上是一个剪切与断裂相结合的过程。 如前所述，在金属切削加工中，多余的材料由刚性刀具切除，以获取需要的几何形状、公差和表面光洁度。属于此类加工方法的例子有车削、钻削、铰孔、铣削、牛头刨削、龙门刨削、拉削、磨削、珩磨和研磨。 大多数切削加工 或称机械加工 过程是以两维表面成形法为基础的。也就是说，刀具与工件材料之间需要两种相对运动。一种定义为主运动 决定切削速度 ，另一种定义为进给运动 向切削区提供新的加工材料 。 车削时，工件的回转运动是主运动;龙门刨床刨削时，工作台的直线运动是主运动。车削时，刀具连续的直线运动是进给运动;而在龙门刨床刨削中，刀具间歇的直线运动是进给运动。 切削速度v是主运动中刀具 在切削刃的指定点 相对工件的瞬时速度。车 削、钻削和铣削等加工方法的切削速度可以用下式表示: V m,min 式中v为切削速度，其单位为m,min;d是工件上将要切削部分的直径，其单位为m;n是工件或主轴的转速，单位为rev,min。根据具体运动方式不同，v、d和n可能与加工材料或工具有关。在磨削进，切削速度通常以m,s为单位度量。 在主运动之外，当刀具或工件作进给运动f时，便产生重复的或连续的切屑切除过程，从而形成所要求的加工表面。进给运动可以是间歇的，或者是连续的。进给速度vf定义为在切削刃的某一选定点上，进给运动要对于工件的瞬时速度。 对于车削和钻削，进给量f以工件或刀具每转的相对移动量 mm,rev 来表示;对于龙门刨削和牛头刨削，进给量f以刀具或工件每次行程的相对移动量 mm,stroke 来表示。对于铣削，以刀具的每齿进给量fz mm,tooth 来表示，fz是相邻两齿间工件的移动距离。所以，工作台的进给速度vf mm,min 是刀具齿数z，刀具每分钟转数n与每齿进给量人的乘积 vf nzfz 。 包含主运动方向和进给运动方向的平面被定义为工作平面，因为该平面包含决定切削作用的两种基本运动。 车削时的切削深度α 有时也被称为背吃刀量 是刀具切削刃切进或深人工件表面内的距离。切削深度决定工件的最终尺寸。在车削加工中采用轴向进给时，切削深度可以通过直接测量工件半径的减少量来确定;在车削加工中采用径向进给时，切削深度等于工件长度的减少量。在钻削中，切削深度等于钻头直径。对于铣削，切削深度定义为侧吃刀量αe，它等于铣刀径向吃刀深度，而铣刀轴向吃刀深度 背吃刀量 被称为αp。 未变形状态时的切屑厚度h，就是在垂直于切削方向的平面内垂直于切削刃 测量得到的切屑厚度。切削后的切屑厚度 即切屑实际厚度h2 大于未变形时的 切屑厚度，也就是说切削比或者切屑厚度比r h1/h2总是小于1。 ‘ 未变形状态的切屑宽度b，是在与切削方向垂直的平面内沿切削刃测得的切 屑宽度。 对于单刃刀具切削加工，切削面积A是未变形的切屑厚度h1和切屑宽度b 的乘积 即A h1b 。切削面积也可以用进给量f和切削深度α表示如下: H1 fsink 及 b a,sink 式中x为主偏角 即切削刃与工作平面形成的夹角 。 因此，可以由下式求出切削面积 A fa 英文原文: Lathes And It’s Cutting Process 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 lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the workpiece. Consequently, more lathes of various types are used in manufacturing than any other machine tool. The essential components of a lathe are the bed, headstock assembly, tailstock assembly, carriage assembly, 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 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 fiat way in one or both sets. They are precision-machined to assure accuracy of alignment. On most modem lathes the ways are surface-hardened to resist wear and abrasion, but 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 headstock is mounted in a fixed position on the inner ways,usually at the left end of the bed. It provides a powered means of rotating the work at various speeds. Essentially, it consists 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 8 to 18 speeds, usually in a geometric ratio, and on modem 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. Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy beatings, usually preloaded tapered roller or ball types. The spindle has a hole extending through its length, through which long bar stock can be fed. The size d this hole is an important dimension of a lathe because it detemtines the imum size of bar stock that can be machined when the material must be fed through spindle. 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 movedtransversely upon it, on some type of keyed ways, to permit aligning the tailstock and headstock spindles. The third major component of the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76 mm 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 size of a lathe is designated by two dimensions. The first is known as the swing. This is the imum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways. The second size dimension is the imum distance between centers. The swing thus indicates the imum workpiece diameter that can be turned in the lathe, while the distance between centers indicates the imum length of workpieee that can be mounted between centers. Engine lathes are the type most frequently used in manufacturing. llley are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest. They commonly range in size from 305 to 610 mtn 12 to 24 inches swing and from 610 to 1 219 mm 24 to 48 inches center distances, but swings up to 1 270 mm 50 inches and center distances up to 3 658 mm 12 feet are not tmcommon. Most have chip pans and a built-in coolant circulating system. Smaller engine lathes--with swings usually not over 330 mm 13 inches --also are available in bench type,designed for the bed to be mounted on a bench or cabinet. Although engine lathes are versatile and very useful, because of the time required for changing and setting tools and for making measurements on the workpiece, they ale not suitable for quantity production. Often the actual chip-production time is less than 30% of the total cycle time. In addition, a skilled machinist is required for all the operations, and such persons are costly and often in short supply. However, much of the operator's time is consumed by simple, repetitious adjustments and in watching chips being made. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw machines, and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing. The engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered. The engine lathe has been replaced in today's production shops by a wide variety of automatic lathes such as automatic tracer lathes, turret lathes, and automatic screw machines. All the advantages of single-point tooling for imum metal removal, and the use of form tools for finish and accuracy, are now at the designer's fingertips with production speeds on a par with the fastest processing equipment on the scene today. Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be careful in using tolerances of an experimental part that has been produced on the engine lathe by a skilled operator. In redesigning an experimental part for production, economical tolerances should be used. Production machining equipment must be evaluated now, more than ever before, in terms of ability to repeat accurately andrapidly. Applying this criterion for establishing the production qualification of a specific method, the turret lathe merits a high rating. In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the optimum tolerances possible on the turret lathe, the designer should strive for a minimum of operations. Generally, automatic screw machines fall into several categories; single-spindle automatics, multiple-spindle automatics and automatic chucking machines.Originally designed for rapid, automatic production of screws and similar threaded pans, the automatic screw machine has long since exceeded the confines of this narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities play an important pm't in the economy of the parts machined on the automatic screw machine.Quantities less than 1 000 parts may be more economical to set up on the turret lathe than on the automatic screw machine. The cost of the pans machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantities. Since surface roughness depends greatly upon material tumed, tooling, and feeds and speeds employed,minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerances. In some cases, tolerances of ?0.05mm are held in continuous production using but one cut. Groove width can be held to ? 0.125mm on some parts. Bores and single-point finishes can be held to ?0.0125mm. On high-production runs where imum output is desirable, a minimmn tolerance of ? 0. 125mm is economical on both diameter and length of turn. Metal-cutting processes are extensively used in the manufacturing industry. They are characterized by the fact that the size of the original workpieee is sufficiently large that the final geometry can be circumscribed by it, and that the unwanted material is removed as chips, particles, and so on. The chips are a necessary means to obtain the desired tolerances, and surfaces. The amount of scrap may vary from a few percent to 70% - 80% of the volume of the original work material. Owing to the rather poor material utilization of the metal-cutting processes, the anticipated scarcity of materials and energy,and increasing costs, the development in the last decade has been directed toward an increasing application of metal-forming processes. However, die costs and the capital cost of machines remain rather high; consequently, metal-cutting processes are, in many cases, the most economical, in spite of the high material waste, which only has value as scrap. Therefore,it must be expected that the material removal processes will for the next few years maintain their important position in manufacturing.Furthermore,the development of automated production systems has progressed more rapidly for metal-cutting processes than for metal-forming processes. In metal-cutting processes, the imprinting of information is carried out by a rigid medium of transfer the tool , which is moved relative to the workpiece, and the mechanical energy is supplied through the tool. The final geometry is thus determined from the geometry of the tool and the pattem of motions of the tool and the workpiece. The basic process is mechanical: actually, a shearing action combined with fracture. As mentioned previously, the unwanted material in metal-cutting processes is removed by a rigid cutting tool, so that the desired geometry, tolerances, and surface finish are obtained. Examples of processes in this group are turning, drilling, reaming, milling,shaping, planing, broaching, grinding, honing, and lapping. Most of the cutting or machining processes are based on a tw, dimensional surface creation, which means that two relative motions are necessary between the cutting tool and the work material. These motions are defined as the primary motion, which mainly determines the cutting speed, and the feed motion, which provides the cutting zone with new material. In turning the primary motion is provided by the rotation of the workpiece, and in planing it is provided by the translation of the table; in turning the feed motion is a continuous translation of the tool, and in planing it is an intermittent translation of the tool. The cutting speed v is the instantaneous velocity of the primary motion of the tool relative to the workpieee at a selected point on the cutting edge . The cutting speed for turning, drilling, and milling processes can be expressed as v dn m/min Where v is the cutting speed in m/min,d the diameter of the workpiece to be cut in meters, and n the workpiece or spindle rotation in rev/min. Thus v, d, and n may relate to the work material or the tool, depending on the specific kinematic pattern. In grinding the cutting speed is normally measured in m/s. The feed motion f is provided to the tool or the workpiece and, when added to the primary motion, leads to a repeated or continuous chip removal and the creation of the desired machined surface. The motion may proceed by steps or continuously. The feed speed vf is defined as the instantaneous velocity of the feed motion relative to the workpiece at a selected point on the cutting edge . For mining and drilling, the feed f is measured per revolution mm/rev of the workpiece or the tool; for planing and shaping f is measured per stroke mm/stroke of the tool or the workpiece. In mining the feed is measured per tooth of the cutter fz mm/tooth ; that is, fzis the displacement of the workpiece between the cutting action of two successive teeth. The feed speed vf mm/rain of the table is therefore the product of the number of teeth z of the cutter, the revolutions per minute of the cutter n, and the feed per tooth vf nzfz . A plane containing the directions of the primary motion and the feed motion is defined as the working plane, since it contains the motions responsible for the cutting action. In turning the depth of cut a sometimes also called back engagement is the distance that the cutting edge engages or projects below the original surface of the workpiece. The depth of cut determines the final dimensions of the workpiece. In taming, with an axial feed, the depth of cut is a direct measure of the decrease in radius of the workpiece and with radial feed the depth of cut is equal to the decrease in the length of workpiece. In drilling, the depth of cut is equal to the diameter of the drill. For milling, the depth of cut is defined as the working engagement ae and is the radial engagement of the cutter. The axial engagement back engagement of the cutter is called ap. The chip thickness hi in the undeformed state is the thickness of the chip measured perpendicular to the cutting edge and in a plane perpendicular to the direction of cutting. The chip thickness after cutting i. e., the actual chip thickness h2 is larger than the undeformed chip thickness, which means that the cutting ratio or chip thickness ratio r h1/h2 is always less than unity. Chip Width The chip width b in the tmdeformed state is the width of the chip measured along the cutting edge in a plane perpendicular to the direction of cutting. For single-point too! operations, the area of cut A is the product of the undeformed chip thickness h l and the chip width b i.e., A h1b . The area of cut can also be expressed by the feedf and the depth of cut a as follows: H1 f sink and b a/sink Where k is the major cutting edge angle i. e., the angle that the cutting edge forms with the working plane . Consequently, the area of cut is given by A fa