中英文翻译镗削加工和镗床.doc

英文翻译原文:(一)BORING AND BORING MACHINESAs carried out on a lathe, boring produces circular internal profiles in hollow work-pieces or on a hole made by drilling or another process, Boring is done with cutting tools that are similar to those used in turning. Because the boring bar has to reach the full length of the bore, tool deflection and, therefore, maintainance of dimensional accuracy can be a significant problem.The boring bar must be sufficiently stiffthat is, made of a material with high elastic modulus, such as tungsten carbide to minimize deflection and avoid vibration and chatter. Boring bars have been designed with capabilities for damping vibration.Although boring operations on relatively small work-pieces. Can be carried out on a lathe, boring mills are used for large work-pieces. These machines are either vertical or horizontal, and are capable of performing operations such as turning, facing, grooving, and chamfering. A vertical boring machine is similar to a lathe but has a vertical axis of work-piece rotation.The cutting tool (usually a single point made of M-2 and M-3 high-speed steel and C-7 and C-8 carbide) is mounted on the tool head, which is capable of vertical movement (for boring and turning) and radial movement (for facing), guided by the cross-rail. The head can be swiveled to produce conical (tapered) surfaces.In horizontal boring machine, the work-piece is mounted on a table that can move horizontally in both the axial and radial directions. The cutting tool is mounted on a spindle that rotates in the headstock, which is capable of both vertical and longitudinal movements. Drills, reamer, taps, and milling cutters can also be mounted on the machine spindle.Boring machine are available with a variety of features. Although work-piece diameters are generally 1 m-4 m(3ft-12ft),work-piece as large as 20 m(60ft) can be machined in some vertical boring machines. Machine capacities range up to 150 kw (200hp).these machines are also available with computer numerical controls, which allow all movements to be programmed. With such controls, little operaror involvement is required and consistency and productivity are improved. Cutting speeds and feeds for boring are similar to those for turning.(For capabilities of boring operations)Jig borers are vertical boring machines with high precision bearings. Although they are available in various sizes and used in tool rooms for making jigs and fixtures, they are now being replaced by more versatile numerical control machines.Design considerations for boring. Guidelines for efficient and economical boring operations are similar to those for turning. Additionally, the following factors should be considered：a. Whenever possible, through holes rather than blind holes should be specified.(The term blind hole refers to a hole that does not go though the thickness of the work-piece )b. The greater the length to bore-diameter ratio, the more difficult it is to hold dimensions because of the deflections of the boring bar due to cutting forces.c. Interrupted internal surfaces should be avoided. （2）Fundamentals of Machine ToolsIn many cases products form the primary forming processes must undergo further refinements in size and surface finish to meet their design specifications. To meet such precise tolerances the removal of small amounts of material is needed. Usually machine tools are used for such operation.In the United States material removal is a big business-in excess of $ per year, including material, labor, overhead, and machine-tool shipments, is spent. Since 60 percent of the mechanical and industrial engineering and technology graduates have something connection with the machining industry either through sale, design, or operation of machine shops, or working in related industry, it is wise for an engineering student to devote some time in his curriculum to studying material removal and machine tools.A machine tool provides the means for cutting tools to shape a workpiece to required dimensions; the machine supports the tool and the workpiece in a controlled relationship through the functioning of its basic members, which are as follow:(a) Bed, Structure or Frame. This is the main member which provides a basis for, and a connection between, the spindles and slides; the distortion and vibration under load must be kept to a minimum. (b) Slides and Sideways. The translation of a machine element (e.g. the slide) is normally achieved by straight-line motion under the constraint of accurate guiding surfaces (the slideway).(c) Spindles and Bearings. Angular displacements take place about an axis of rotation; the position of this axis must be constant within extremely fine limits in machine tools, and is ensured by the provision of precision spindles and bearings.(d) Power Unit. The electric motor is the universally adopted power unit for machine tools. By suitably positioning individual motors, belt and gear transmissions are reduced to a minimum.(e) Transmission Linkage. Linkage is the general term used to denote the mechanical, hydraulic, pneumatic or electric mechanisms which connect angular and linear displacements in defined relationship.There are two broad divisions of machining operations:(a) Roughing, for which the metal removal rate, and consequently the cutting force, is high ,but the required dimensional accuracy relatively low .(b) Finishing, for which the metal removal rate, and consequently the cutting force, is low, but the required dimensional accuracy and surface finish relatively high .It follows that static loads and dynamic loads, such as result form an unbalanced grindingwheel, are more significant in finishing operations than in roughing operations, The degree of precision achieved in any machining process will usually be influenced by the magnitude of the deflections, which occur as a result of the force acting.Machine tool frames are generally made in cast iron, although some may be steel casting or mild-steel fabrications. Cast iron is chosen because of its cheapness, rigidity, compressive strength and capacity for damping the vibrations set-up in machine operations, To avoid massive sections in castings, carefully designed systems of ribbing are used to offer the maximum resistance to bending and torsional stresses. Two basic types of ribbing are box and diagonal. The box formation is convenient to produce, apertures in walls permitting the positioning and extraction of cores. Diagonal ribbing provides greater torsional stiffness and yet permits swarf to fall between the sections; it is frequently used for lathe beds. The slides and slideways of a machine tool locate and guide members which move relative to each other, usually changing the position of the tool relative to workpiece .The movement generally takes the form of translation in a straight line, but is sometimes angular rotation, e.g. tilting the wheel-head of a universal thread-grinding machine to an angle corresponding which the helix angle of the workpiece thread. The basic geometric elements of slides are flat, vee, dovetail and cylinder. These elements may be used separately or combined in various ways according to the applications . Features of slideways are as follows :(a) Accuracy of Movement. Where a slide is to be displaced in a straight line, this line must lie in two mutually perpendicular planes and there must be no slide rotation. The general tolerance for straightness of machine tool slideways is 00.02mm per 1000mm; on horizontal surfaces this tolerance may be disposed so that a convex surface results, thus countering the effect of "sag" of the slideway.(b) Means of Adjustment. To facilitate assembly, maintain accuracy and eliminate "play" between sliding members after wear has taken place, a strip is sometimes inserted in slides. This is called a gibstrip. Usually, the gib is retained by socket-head screws passing through elongated slots；and is adjusted by grub-screws secured by lock nuts.(c) Lubrication. Slideways may be lubricated by either of the following systems：1)Intermittently through grease or oil nipples, a method suitable where movements are infrequent and speed low2) Continuously e.g. by pumping through a metering valve and pipe-work to the point of application; the film of oil introduced between surfaces by these means must be extremely thin to avoid the slide “floating”If sliding surfaces were optically flat oil would be squeezed out，resulting in the surfaces sticking. Hence in practice slide Sill"faces are either grourld using the edge of a cup wheel，or scraped. Both processes produee minulte surface depressions，which retainpocket” of oil, and complete separation of the parts may not occur at all points.(d) ProtectionTo maintain slideways in good order, the following conditions must be met：1) Ingress of foreign matter，egswarf，must be prevented. Where this is no possible，it is desirable to have a form of slideway，which does not retain swarf，e.g. the inverted vee.2) Lubricating oil must be retainedThe adhesive property of oil for use on vertical or inclined slide surface is important; oils are available which have been specially developed for this purpose. The adhesiveness of oil also preverts it being washed away by cutting fluids3) Accidental damage must be prevented by protective guards译文:(一)镗削加工和镗床像车床加工零件一样，镗床能在中空的工件或由钻削加工或其它工艺所加工的孔上进行内轮廓圆的加工。镗削是由那些类似车削的刀具完成的。因为镗头必须达到镗杆的全长，刀具将发生弯曲，因此，尺寸精度的保持性成为了一个重大问题。镗杆必须有足够的刚度刀杆是由较高弹性模量的材料制造的，比如碳化钨（硬质合金）去减小弯曲和避免摇动和振动。镗杆被设计有减振的能力。镗床既能加工在车床上加工的较小工件，镗铣床又能加工巨大的工件。这类机械既有立式的又有卧式的并且能够完成如：车削、车端面、切槽、和倒角。一台立式的镗床类似一台车床，但它有一根垂直的工件旋转轴。刀具（通常用于切削的单独切削点是由M-2和M-3高速钢和C-8硬质合金制造的）被安装于能垂直运动（用于镗削和车削）和径向运动（用于车端面）并由十字导轨导向的刀头上。刀头能够旋转去加工圆锥形表面。在卧式镗床上工件被装夹在能在水平面内两个轴向和径向上移动的工作台上，刀具被安装于能做垂直和纵向两方向上运动的主轴箱上。钻头、铰刀、螺纹刀和铣刀都能安装于机床主轴上。镗床具有许多优良的性能，它所加工工件的直径是1m-4m(3ft-12ft)，工件尺寸达到20m(60ft)的可在专用的立式镗床上加工。机床功率范围可达到150kw(200hp)。这些可用于所有运动都能编程的数字控制加工。利用这些控制，只需要很少的相关操作，并且稳定性和生产率大大提高了。镗床的切削速度和进给速度和车床比较相似。坐标镗床是属于具有较高精度支撑的立式镗床。尽管它们可用于各类尺寸的工件加工和拥有夹紧合安装的刀具空间。它们正被多功能的数控机床取代。镗床的设计要求：导轨的效率，类似于车削的经济型操作，另外，应该考虑以下因素：a.无论何时，应尽可能注意是加工通孔而并盲孔。（盲孔系列是指那些没有穿国工件厚度的孔）b.应该控制径向进给速率，很难去支撑径向，因为切削力引起镗杆的弯曲变形。c.应该避免交叉的内表面加工。（2）机床基础为了满足规定的设计规格，大多数情况下初步加工的产品都必须再经过进一步的尺寸和表面的精加工。要达到这样的精确规定公差的要求，少量材料需要被切除掉，而机床通常就是用于此种操作。在美国，材料切除是一项大业务每年这方面的支出超过36×109美元，包括材料、劳力和机床运输。60%的机械工程和工业工程毕业生都通过贸易、设计、机械修理工厂，或通过在相关行业工作而与机械工业密不可分，因而如果他们花费一定的时间精力来学习这个领域中的材料切除和机床技术的话会是很明智的选择。机床提供切割工具的方式，以使工件成型，达到规定的尺寸；此种机器依靠其基础部件的运作来掌握工具和工件之间的联系。其基础部件的运作如下： 床身、构造和框架。这三种主要的部件为锭子和滑移的基础，并将它们联系起来；操作中的变形和震动必须尽量避免。 滑移与滑轨。机械部件（如滑移）的转换通常是通过在精密的指导表面（滑轨）的控制下做直线运动而完成的。 锭子与轴承。角位移是围绕一个旋转轴线发生的；这个转轴的位置必须一直处于严格精确的限制之中，并由精密锭子和轴承提供保障。 动力仪器。电动机是被广泛应用于机床的动力仪器。通过将各电动机放置于合适的位置，传输带和齿轮运输会被降低到最低限度。 传输联接。联接是一个通常用来指机械驱动的、水压驱动的、气压驱动的和电力驱动的机械装置，将有角移置和直线移置联系起来，使其符合规定。加工操作大体上分为两类： . 粗加工。其金属切除率高且由此导致的切除力较大，但规定的尺寸精度相对较低。 . 精加工。其金属切除率低且由此导致的切除力较小，但规定的尺寸精度相对较高。静载荷及动载荷，如处于非平衡状态的砂轮所导致的结果，自然在精加工方面比在粗加工操作方面更为重要。任何加工过程所达到的精确度通常会受到偏差大小的影响，这种影响是是操作动力的结果。机床框架通常由铸铁制造，虽然有些机床可能为钢铸件或低碳钢结构。选择铸铁是因为其价格、硬度、耐压强度及减少加工操作中的震动的能力。为了避免铸件出现轻重不均的部分，精心设计的肋材构架系统被采用，最大可能地抵抗造成弯曲和变形的压力。两种肋材构架分别为箱形和对角线形。箱形结构便于生产，因为壁上的孔径允许核心的定位和抽取。对角线楞条配置则提供更大的抗纽刚度并允许金属屑从部件当中的孔隙落出，因此经常被用于机床。车床的滑移和滑轨指引并且为相互影响运动的部件定位，通常根据工件更改车床的位置。运动一般采取直线运动的形式，但有时是旋转，例如，对应于工件的螺纹螺旋角方向而转动万能螺纹磨床上的砂轮头的一个角度。基本的对称滑移部件为扁平、V形、燕尾槽形及汽缸形。这些部件既可单独使用又可根据用途以不同方式组合使用。滑轨的特征如下： 如果滑移要在一条直线上移动位置，这条直线必须位于两个相互垂直的平面之间且必须没有滑动旋转。 机床滑轨的直线性规定公差一般介于00.02mm/100mm之间；在水平表面此公差可以被处理以得到凸形表面这样就可以抵消滑轨下沉的作用。 润滑油。滑轨可能被以下两种系统中的任何一种润滑： 间歇通过油脂或油嘴润滑。这种方法适合运作不频繁和速度不高的情况。 持续润滑，如通过计量阀和管道根据需要抽取；通过这些方法操作的表面之间的润滑油薄膜必须非常薄，以避免滑移漂浮。如果滑移表面是镜平面，油就会被挤出，使表面粘接。因此实际操作中滑移表面不是被杯状轮边缘压平，就是被刮去。两种操作过程都会产生微小的表面凹痕，这种凹痕会导致少量润油存留，而且零件的完全分离可能不会总是发生；因此，滑移的正确定位得到保留。 保护。为了维护滑轨，使其正常工作，必须满足如下条件： 必须避免外来物质如铁屑的进入。如果这种条件不可能满足，则应该采用不会滞留铁屑的，如倒V形的滑移。 润滑油必须保留。润滑油在垂直的或倾斜滑移表面上的粘性特质非常重要；特制的润滑油市场有售。润滑油的粘性同时能防止其被切削液冲走。 必须防止由保护装置导致的意外损坏。