专业英语作业2

1、 机械工程专业英语作业 课文翻译 40 本文一共十五段,合作人1120112 25 乔思凯 1到8段 1120112 26 张瑞峰 9到15段 40 Precision of machine tools 机床精度 Modern machine tools are marvels of near perfection. Consider a lathe producing round pieces to a tolerance of 50 m. That is expected performance; yet it means that the machine maintains a rela

2、tionship between a whirling workpiece and gliding tool within 25 m on a side and does it over and over again. That dimension is less than half the thickness of a human hair.译文:考虑到一个车床生产公差50M的圆形件,现代机床是近乎完美的奇迹。那正是所期望的,然而，这意味着机器的维护一个旋转的工件和工具的公差在25微米范围内的波动,需要一边做了一遍又一遍的工作.这次村比人体头发厚度的一半还要小. To turn to a t

3、olerance of 25 m on a side, the tool first must be adjusted to within 12.5 m of exact size. Such a minute amount can scarcely be seen, and the machine has to magnify it to reveal it to the crude vision of the operator. Then as metal is slashed away with tremendous force at varying depth, the machine

4、 must guide the tool along a firm course and hold the workpiece steady so that neither deviates from the other by more than 12.5 m and this is not close work. Tolerances smaller than 2.5 m are held in some operations.译文:要保持对侧25的公差微米，工具首先必须调整到12.5米的精确尺寸.这种微量几乎可以看出，本机还具有放大去揭示它对操作者粗略影像。当金属在不同的深度被极大的外力切

5、削掉,机器必须沿一个特定的路线引导工具并保持工件平稳，不偏离其位置超过12.5微米_这不是密切工作,小于2.5微米的公差也出现于某些操作中. Errors in the work done by a machine tool are caused by (a) inaccuracy in its construction, (b) deflection, (c) wear, (d) thermal expansion, (e) dirt, and (f) human laxity. Good design and operation of a machine tool depend upon

6、observing principles that keep errors small. Evidences of these principles are found in the structural members, the bearings and guideways for straight and rotary motions, the measuring devices, and the standards of construction of all good machine tools.译文:机床工作中出现的错误是由(a)加工误差(b)偏转(c)装配(d)磨碎和热膨胀(e)污

7、垢(f)人为松动等造成的.好的设计和机床的操作取决于其观察原则，保持小的误差。这些原则的依据是在各结构中发现，如直线和旋转运动的轴承和导轨，测量装置，和所有好的机床结构标准。 Design for control of errors is especially important for automated machine tools, such as for numerical control, than for simpler manual machines, where the operator can compensate for errors.译文:控制误差的设计自动化机床尤其重要，

8、如数控，比简单的手动机器，操作者可以弥补错误。 Structural Members An evident feature of all major machine tool members is rigidity. The components of standard machine tools made in lots are most often cast, but some, and especially special units, are built up by welding steel plates and sections together.译文: 结构构件 很明显各结构构件

9、都是刚性的,标准机床的组成部分一般都是铸造而成.但也有一些，尤其是特殊的单位，是由钢板和型材焊接在一起。 One purpose of rigidity in machine tool design is to keep deflections small and maintain true alignments. The principles of mechanics show that deflection of a machine member is inversely proportional to the cube of its depth in the direction of a

10、n applied load. For that reason, a machine tool section is deep in the direction of the main force and heavily ribbed and wide to take other forces and moments.译文:机床刚度的的设计,目的之一就是要保持变形小和保持真实的路线,力学原理表明，机械构件挠度与在其深度施加的负荷的立方成反比。出于这个原因,一个机床在其主要受力方向深度大且装以厚重肋以承载其他的力和力矩。 Machine tool components are designed

11、not only to be rigid, but to have the most rigidity with the least possible weight. One obvious reason is that a machine has to be moved, at least from where it is made to where it is used. A second reason is that rigidity with small mass avoids vibration, and raises machine productivity. A third re

12、ason is that moving components are more easily and thus accurately controlled with less inertia, of particular importance in automatic control.译文:机床部件的设计不仅是刚性的，并且使用尽可能少的重量的材料以有最大的刚度。一个明显的原因是机器必须要被被转移，至少从产地到使用地。第二个原因是大刚度小质量可以避免振动，提高机器的生产率。第三个原因是，运动部件更容易和精确地控制，惯性小，在自动控制中的有特别重要. For a simple case, any

13、object with a single degree of freedom has a natural frequency in cycles per second of W n= k/m .The factor m is the mass of the structure, and k is proportional to the stiffness of the object. Thus the stiffer the member and the less its mass, the higher is its natural frequency. A high natural fre

14、quency is desirable because it is less excited by the usual disturbances.译文:一个简单的例子，任何一个单自由度的对象在每个周期都有一个固有频率W n = K / M。该因子m为结构的质量，和k是对象的刚度比例。因此，部件刚性越大和质量越小，更高的是它的固有频率。较高的自然频率是可取的,因为它不受通常干扰的影响。 Guideways The preparation of guideways in machine tools requires significant effort. T

15、he requirements of guideways are high accuracy, low surface roughness, low value of frictional force and low wear rate.译文:导轨 机床导轨的制备需要很大的努力。导轨的要求是高精度，低的表面粗糙度，摩擦和低磨损率。 The types of guideways may be classified as guideways with sliding friction also termed slideways and guideways with rolling friction

16、 also termed as antifriction guideways.译文:导轨类型可分为滑动摩擦导轨和滚动摩擦的减摩导轨。 There are a number of slideways conventionally used n machine tools. They are V-slideways, flat slideways, and dove tails.译文:有一些常用的n型机床导轨。他们v型滑轨，平导轨，燕尾槽. Anti-friction guideways involve intermediate rolling members ( balls or rollers

17、) between the sliding members, thus reducing the friction. 译文:减摩导轨包含中间滚动部件（滚珠或滚柱）在滑动部件之间，从而降低摩擦。 Spindles The members that revolve workpieces or cutters on machine tools are called spindles. Most machine tool spindles today run in antifriction bearings. Roller bearings, usually tapered, are used for

18、 heavy service at low and moderate speeds. Ball bearings run freely, stand up at high speeds, and are favored for light service. For the highest precision, ball bearings are preloaded and selected in matched sets to minimize runout. Pressurized gas journal bearings of high rigidity with low friction

19、 are used for high spindle speeds.译文:主轴 机床中包含工件或刀具的部分被称为主轴。大多数机床主轴在减摩轴承上运行。滚子轴承，通常是锥形的，在低和中等速度起到重要作用。球轴承运行自如,拥有高速度,在轻服务中受到青睐.为追求高精度，球轴承的预紧和成套的选择要减少跳动。具有低摩擦,高刚度气体静压轴颈轴承用于高转速主轴的运行。 Thermal Distortion Machine tool members get hot during operation, and the temperature rise is not uniform as a rule. This

20、 means that some members expand more than others, and alignments and settings change. This is most noticeable during the first two hours of operation of a machine tool, and usually conditions become stable after equilibria of temperatures are reached. A turret lathe running at 1 000 rpm can be taken

21、 as an example. During the first hour the temperature rose about 17 in the headstock, and the spindle moved 50 m upward and 180 m sideward. During the second hour, spindle movements were 10 m up and 2.5 m to the side. Room temperature change also has an affect; a day to night temperature difference

22、of 4.5 is reported to have caused a large vertical tracer lathe to drift by 80 m. A skilled operator can do much to compensate for temperature changes, but the problem is more difficult with automatic systems.译文:热畸变 机床的组件在操作中变热，而温度的上升是不均匀的。这意味着，一些组件温度的扩大超过其它组件，另外,对齐和设置的变化。这在一个机床前两个小时的操作中是最明显的，通常情况趋于

23、稳定是在温度达到平衡后。一个转塔车床在1000 RPM 下运行可以作为一个例子。在第一个小时的温度在主轴上升高了17，主轴向上移动了50微米,向侧旁移动了180微米。在第二个小时，主轴运动向上了10 微米和向侧旁移动了2.5微米。房间温度的变化也有影响；报道显示,一天4.5昼夜温差引起了大型立式车床示踪剂漂移了80微米.一个熟练的操作员可以做很多事情来补偿温度变化造成的影响，但对自动系统问题更加困难. Heat sources that cause distortion may be in the environment, the fabricating or cutting process and in th