【机械类毕业论文中英文对照文献翻译】机械元件的设计
【机械类毕业论文中英文对照文献翻译】机械元件的设计,机械类毕业论文中英文对照文献翻译,机械类,毕业论文,中英文,对照,对比,比照,文献,翻译,机械,元件,设计
Design of Machine Elements and noise Control This article, as the title indicates, will not deal with the broader aspects of the design of complete machines, but will attempt to explain the fundamental principles required for the correct design of the separate elements which compose the machine. The principles of design are of course universal .The same theory or equations may be applied to a very small part, as in an instrument, or to a larger but similar part used in a piece of heavy equipment. In no case, however, should mathematical calculations be looked upon as absolute and final. They are all subject to the accuracy of the various assumptions which must necessarily be made in engineering work. Sometimes only a portion of the total number of parts in a machine are designed on the basis of analytic calculations . The form and size of the remaining parts are then usually determined by practical considerations. On the other hand, if the machine is very expensive , or if weight is a factor, as in airplanes, design computations may then be made for almost all the parts. The purpose of the design calculation is of course to attempt to predict the stress or deformation in the part in order that in may safely carry the loads which will be imposed upon it, and that it may last for the expected life of the machine. All calculations are, of course, dependent on the physical properties of the construction materials as determined by laboratory tests. A rational method of design attempts to take the results of relatively simple and fundamental tests and apply them to all the complicated and involved situations encountered in present-day machinery. In addict in, it has been amply proved that such details as surface condition, manufacturing tolerances, and heat treatment have a marked effect on the strength and useful life of a machine part .The design and drafting departments must specify completely all such particulars, and thus exercise the necessary close control over the finished product.Training in rapid and accurate numerical work is invaluable to the designer. The designer should keep an accurate notebook, as it is frequently necessary for him to refer to work which he has done in the past. A sketch, carefully drawn to scale, is also a necessity, and provides a convenient place for putting down a portion of the data used in connection with the problem. It goes without saying that all data, assumptions , equations, and calculations should be written down in full in order to be intelligible when referred to at a later date.Influence of Machine Tool on Machining Accuracy A machine tool has the following functions in the machining process:Clamping of the tool and workpiece and establishing their correct relative position.Supplying the working motions (primary and auxiliary motion)and maintaining the correct relative position of the workpiece and tool during the machining operation.Supplying the energy for cutting or erosion work.Machining accuracy is evaluated by considering the difference between the desired (nominal) dimensions and properties and those of the finished product. The smaller are the machining errors, the greater is the accuracy. The machine tool influences machining errors by:Errors in workpiece positioning in relation to the tool. This may be caused by errors in the production and assembly of machine tool parts and assemblies and by errors in the positioning and clamping of the workpiece and tool relative to the machine tool. It is called in short the geometric influence on machining accuracy;Errors in the working motions of the tool and workpiece during the machining process, or kinematic influence on machining accuracy;Errors in the displacement of machine tool parts and assemblies, workpiece and tool as a result of forces appearing in the machining process, called dynamic influence on machining accuracy.Errors in the displacement of machine tool parts and assemblies, workpiece and tool as a result of thermal expansion cause by heat generated in the machining process and as a result of friction in the driving mechanisms. This is called thermal influence on machining accuracy. Geometric errors on a machine tool should wherever possible be measured directly. Their evaluation depends on the absolute magnitude of the error and on the sense of deviation from nominal dimensions. Errors whose sense indicates that, as the wear sets in, they will decrease, are considered to be less harmful.The importance of geometric errors for total machining accuracy is relatively great. This can be demonstrated on the basis of a statistical comparison of errors measured on finished products with errors calculated from geometric deviations only. Some statistical reference denotes the share of geometric errors in total machining errors varies within a range of 50%75%.Thus a conclusion can be drawn that geometric errors in machine tools should be reduced as far as possible, but still within limits of an economically justified accuracy.In the case of machine tools with complex working motions, the kinematic accuracy of the machine tool is of great importance. This can be observed when machining gears, threads and other curved surfaces.The kinematic accuracy of a machine tool results from the accuracy of coupling of its internal kinematic chains. A kinematic error is defined by deviations of the final and initial link of a kinematic chain from nominal positions or displacements. Kinematic errors may be calculated or measured by means of special instruments called kinematic meters.Checking of kinematic errors has not yet become a widespread practice and ther are no standards establishing their permissible values, just as there are no standards concerning geometric errors. One of the main reasons why the measurement of kinematic accuracy has not spread is that relatively complicated and expensive equipment is necessary , together with time-consuming operations. The noise control problem can be broken down into three segments including the design concept , the design fix and the acoustic fix .The latter tow fixes will probably overlap in most cases and interact with each other while the design concept will set the constraints for the overall problem .The definition of the problem is usually general in mature and arises most often from a complaint of someone or some group segment of the population.Identifying the sources does not usually require sound measurements at this juncture although those measurements will be required prior to attempting those procedures indicated in the “Design Fix” column . Of great importance in the design concept stage is the correct identification of the population affected by the source , that is ,the receive and the path of propagation to them . Having identified the people affected by the noise source, it is necessary to examine the acceptable noise limitations to be imposed upon or accepted by those individuals . Are these limits those which are established or imposed by existing criteria either legal or otherwise or are there peculiar conditions which makes this problem unique , for example , is there a conditioned population in a generally high noise environment such as that which exists in major urban centers ? Prior to a design fix and as part of the design concept ,the restraints to the design must be examined . Are there legal limitations ? Is the problem such that the maximum noise exposure for established time periods has been promulgated by such laws as the Federal Occupational Safety and Health Act ? Is the maximum source level specified by a federal agency such as the aircraft noise emission limits established by the Federal Aviation ? The operation and maintenance requirements must be critically reviewed . Constraints imposed by required access to interior parts , say ,to safety switches for either operation or maintenance , must be viewed at the design stage , and particularly if the design involves the attempted noise reduction lf an existing piece of machinery . Consultation with experienced operators at this stage can save many potential redesign requirements after the design is fixed . We must address the social aspects lf the problem . The esthetics lf the final design should be considered here . Will the final design enhance the visual parameters of the problem ? Will the result lf the acoustic fix be a more appealing product ? Giant noise control devices are often faced by engineers involved in the design of power plant facilities to be located close to their customers in inhabited areas . They must decide , for example between the forced draft cooling tower with its large area but low height profile and the inherently quieter natural draft cooling system which requires a structure usually more than 50 000 ft high .The social implications of “no solution should be examined as against a total of partial reduction lf the source noise .To some extent the no-solution concept will have a bearing on the economic constraints imposed on the design concept . Very early in the approach to a solution to a problem of controlling a noise source , the economic constraints must be spelled out . Noise control devices can often be very expensive . Low frequency attenuation is more than the treatment of high frequency sounds . This cost must be weighed against benefits to be obtained . Noise control dollars are often considered nonproductive dollars at first glance by contrast with , for instance ,heat recovery devices which not only save energy but pay for themselves in fuel costs .However , when these dollars are weighed against potential savings in compensatory awards for hearing loss or as the price of a good public relationship with neighbors , they take on a less frightening aspect .When a company with a severe noise problem which is hazardous to their employees is faced with a $ 500 per diem fine or a threat of injunction resulting in the closing of its operations , the cost of a noise control devices ranging up to $ 50 000 or more soon becomes economically viable . When the noise control procedures are inserted at the design stage of a piece of equipment or in the design of a building or highway they can result in altered decisions for materials , processes , and so on ,which can actually result in sayings to the producer, owner , or general public as the case may be . Shorter and more efficient air passages requiring less material (which are thus less costly )have been used . Different and cheaper bearings are all examples which could result in a quieter and at the same time less costly end product . It has been estimated that engineering or consulting costs to perform the above evaluations of design can add as little as one-tenth of one percent of the manufacturing or design costs . Thus to assert that all noise control procedures are costly is a distortion of the field of noise control .1机械元件的设计这篇文章,正如标题表明的,将不处理成套计算机的设计的更宽的方面,但是将试图解释基本原理要求组成机器的单独的要素的正确的设计。设计原则当然普遍。相同的理论或者方程式可以被用于一个非常小的部分,像在一台仪器里,或者对一个更大,但是相似的部分来说,曾在重型设备里使用的那样。然而,数学计算被认为是绝对和最后。 它们全部受影响必须一定被在工程做的各种各样假定的准确工作。 有时只有在一台机器里的部分被根据分析的计算设计。通常剩下部分的形式和大小然后根据实际的考虑被确定。另一方面,如果机器非常昂贵,或者如果重量是一个重要因素,例同在飞机里,那么设计计算可以完全适合几乎所有部分。设计计算的目的当然是试图预测压力或者在部分的变形,为了用将被它强加给建材的物理性能,像在实验室中确定的那样。一种设计尝试的方法用于相对简单和基本的试验的结果并且把它们全部用于所有的现代机械中遇到的错综复杂情况。 另外,它已充分证明这样的细节,像表面条件。热处理对机器零件的强度和使用寿命有被显著的影响。设计和起草的部门必须指定完全全部的这样的细节,因此运用必要密切的手段对最终产品予以控制。在迅速和准确的数字工作里,训练对设计者无价。设计者应该保持一个准确笔记本,让他知道经常必要工作他做过去哪个。画一个草图,仔细按比例描绘,也是一件必需品,并且为放下有关问题使用的数据的部分提供一个便利的地方。不言而喻,全部数据,方程式并且计算过程全被写下,以便被日后使用。2机床对加工精度的影响一台机床在机器加工过程里有下列功能:a) 工件和刀具以及确定它们的正确的位置。 b) 提供工作的运动(主要和辅助运动)并且在机器加工操作期间保持工件和工具的正确的有关的位置。 c) 为切削和腐蚀提供能量。加工精度通过考虑在被期望的(名义上)尺寸和特性和最终产品的之间的差别被评价。机器加工误差越小,精度越高。机床影响机器加工误差就越小。a) 关于刀具在工件的安置误差。这部分误差可能在生产机床零件和主件的装配误差引起,也许通过在工件的位置误差和装夹误差有关的误差产生。简言之,称为机械精度上的几何学影响。b) 在工件的刀具和工件的运动在机器加工过程期间的误差,或者关于加工精度的动态的影响; c) 误差在机床零件和主件的替代内, 工件和刀具由于在机器加工过程里出现的力量,关于加工精度叫动态的影响。d) 工件和刀具由于热膨胀和由于在推动的机械作用的磨擦在机器加工过程内产生,而引起的热使工件、刀具之间产生位移误差。这叫为热变形误差对机械精度的影响。机床零部件和主件在加工精度上的影响,被认为是那些主件和零部件所作关于 工件和刀具的有关的位置有关。例如,在一台车床里这样的组件被认为:主轴箱部件溜板箱部件和尾座部件。实际上,其它装配间接影响工件和刀具的位置,它们的变形和替代可能也引起机器加工误差。因此,通常认为只有与工件和刀具和接触的这个部件的位移误差,才最后决定机床对加精度的影响。只要可能的话,在一台机床上任一位置的几何误差可以被直接测量。它们的评估取决于误差的绝对值的大小和对与规定尺寸的偏离方向。如当机床产生磨损时,误差值将减少,它所产生的误差被认为不那么有害。 总加工精度的几何学误差的重要性相对大。 这可能被证明加工后的产品测得误差同由几何偏差计算得出的误差进行比较就可以证明这一点。分析比较时,反复考虑几何误差、运动误差、动态误差和热变形误差。一些统计资料表明几何学误差在整个机械加工中,误差在50%-75%的范围内变化。 因此一个结论,被得机床里的几何学误差应该被尽可能降低,但是仍在经济证明范围内。 就有运转运动的复杂的机床而论,机床的动态的准确至关重要。 这可能被观察什么时候齿轮,线和其他曲面机器加工。 一台机床的动态的准确起因于它的内部的动态的链配合的准确。 动态的误差被定义为使运动链首端件与实际的位置和位移的偏差决赛的偏差。 动态的误差的检查还没有成为一个广泛的惯例,不是建立它们的容许值的标准, 正像没有关于几何学误差的标准一样。 动态的准确的测量没传播的主要原因之一是相对错综复杂和昂贵的设备是必要的,以及费时的运动。对于复杂运动的机床系统,机床的运动精度是很重要的。在加工齿轮、螺纹、和其它曲面是被奉行。机床的运动精度是由内外传递链的配合精度产生的。运动误差被定义为使运动链首端件与实际位置和位移的偏差。运动误差精度计算和测量,通过被称为位移测定仪的特殊器械来实现。检测运动误差呈现在实践中没有产生广泛确定它们允许值的标准。就像没有关于几何误差的标准。运动精度没有被传播的原因是运动精度需要很贵的设备和耗时的操作。 3. 噪声控制噪声控制可分为三个阶段:包括设计思想、设计的安排、声学。后两种情况在大多数情况下不发生重叠或互相交插。设计思想为整个噪声控制问题确定约束条件,这个问题的定义常常是一般性慨念,它常起因于一些人或某些人群的报怨。此时,定义噪声源常常不需要声音的测量。在设计概念阶段至关重要的是来源影响的人口的正确的鉴定, 即得到的影响给它们途径, 已经鉴定被噪声源影响的人们背后,检查可接受噪音限制被强加给或者由那些个人接受是必要的。如果这些限制是那些,被现有的标准建立或者强加或者法律或者其它。从而使这个问题独特,例如的独特的条件,有一般象那样高环境噪音限制的人口在主要都市中心内存在哪个?在一种设计之前修理,作为设计概念的部分,对设计的约束必须被检查。 有法律限制吗?作那些问题因此那些暴露最大噪音适合建立时间段被被象那些联邦职业安全局和健康部门,有这样的法律颁布行动吗?因为联邦航空公司建立的那样的一个联邦政府机构的约束。最大的极限经常被用于限制像飞机噪音发射限制。操作和维修要求必须被严重地评论。比如说,对操作或者维修的保险开关,要求的内部部分的入口强加的限制条件。一定在设计阶段查看,尤其,在设计要被试图降低噪声的有关现有机器设备。如果,在设计被确定之后,与有经验的操作者的协商在这个阶段能节省很多潜在的重新设计要求。我们必须处理社会方面机器设备的大量噪声问题。我们应该考虑这里最经济设计的美观性问题。设计的最后,将提高问题的视觉参数吗?巨大的噪声设备常被看成是美丽风景的一个污点。使用巨大噪音控制装置经常由熟练用户的设计的工程师面对。它与发电厂是否接近于居住的地区有关。他们常常在在强冷却的冷却塔做出选择,它占地面积大,但高度很低。本来就很安静的自然风凉系统,它需要五万英尺高的结构。无解的社会含义应该针对全部组成部分以减小噪声源。在一定程度上无解的概念将会与强加在设计概念上的经济约束有关。早在一个解决一个控制噪声源的问题方法的约束方面,经济限制条件必须被详细说明。噪音控制装置经常能非常昂贵。低频衰减多于处理高的频率声音。这费用必须权衡好处才可以被获得。乍一看来噪声控制花费的美元经常被认为不是生产的花销。例如,热量回收器不仅可以节省能源,而且在燃料里为它们自己支付的热回收消耗。但是,这些花费被权衡来尽可能节约储蓄适合丧失听力或者作为一种公众与邻居关系的补偿。它们呈现稍微令人担心的方面。什么时候有严厉的噪音问题危害它们雇员的公司面临每天被罚款500 美元,或者是一被次命令关闭它的经营危胁。噪声控制的花费的范围大约在50 000美元左右。在50 000美元范围内的一台噪音控制装置变得在经济上可行。当噪音管理程序被在一台设备的设计阶段插入时或者在一座大楼或者在高速公路的设计过程中,它们能导致改变的材料的决定,处理,等等。实际上得看情况对生产者,拥有人或者普通民众所产生的言论。更短和更有效率的空气通路要求较少的材料(如此不那么昂贵)已经被使用。不同和更便宜的轴承全部是能导致更安静和同时不那么昂贵的最后产物的例子。据估计,那个工程或者咨询花销用于完成上述评估的设计,对上述评估的能增加像生产或者设计的百分之一中的十分之一花费一样的少。因此,认定全部噪音管理步骤和控制观点是一种噪声控制的领域的高消费。
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