机械英汉翻译机械设计概论.doc

原文Introduction to Machine DesignMachine design is the application of science and technology to devise new Or improved products for the purpose of satisfying human needsIt is a vast field of engineering technology which not only concerns itself with the original conception of the product in terms of its size，shape and construction details，but also considers the various factors involved in the manufacture，marketing and use of the productPeople who perform the various functions of machine design are typically called designers，or design engineersMachine design is basically a creative activityHowever，in addition to being innovative，a design engineer must also have a solid background in the areas of mechanical drawing，kinematics，dynamics, materials engineering, strength of materials and manufacturing processes. As stated previously，the purpose of machine design is to produce a product which will serve a need for manInventions，discoveries and scientific knowledge by themselves do not necessarily benefit people；only if they ale incorporated into a designed product will a benefit be derivedIt should be recognized，therefore，that a human need must be identified before a particular product is designed Machine design should be considered to be an opportunity to use innovative talents to envision a design of a product，to analyze the system and then make sound judgments on how the product is to be manufacturedIt is important to understand the fundamentals of engineering rather than memorize mere facts and equationsThere are no facts or equations which alone can beused to provide all the correct decisions required to produce a good designOn the other hand，any calculations made must be done with the utmost care and precisionFor example，if a decimal point is misplaced，an otherwise acceptable design may not functionGood designs require trying new ideas and being willing to take a certain amount of risk，knowing that if the new idea does not work the existing method call be reinstatedThus a designer must have patience，since there is no assurance of success for the time and effort expendedCreating a completely new design generally requires that many old and wellestablished methods be thrust asideThis is not easy since many people cling to familiar ideas，techniques and attitudesA design engineer should constantly search for ways to improve all existing product and must decide what old，proven concepts should be used and what new，untried ideas should be incorporatedNew designs generally have “bugs” or unforeseen problems which must be worked out before the superior characteristics of the new designs can be enjoyed. Thus there is a chance for a superior productbut only at higher riskIt should be emphasized that，if a design does not warrant radical new methods，such methods should not be applied merely for the sake of changeDuring the beginning stages of design，creativity should be allowed to flourish without a great number of constraintsEven though many impractical ideas may arise，it is usually easy to eliminate them in the early stages of design before firm details are required by manufacturingIn this way，innovative ideas are not inhibitedQuite often，more than one design is developed，up to the point where they call be compared against each otherIt is entirely possible that the design which is ultimately accepted will use ideas existing in one of the rejected designs that did not show as much overall promisePsychologists frequently talk about trying to fit people to the machines they operateIt is essentially the responsibility of the design engineer to strive to fit machines to peopleThis is not an easy task，since there is really no average person for which certain operating dimensions and procedures are optimumAnother important point which should be recognized is that a design engineer must be able to communicate ideas to other people if they ale to be incorporatedInitially，the designer must communicate a preliminary design to get management approvalThis is usually done by verbal discussions in conjunction with drawing layouts and written materialTo communicate effectively，the following questions must be answered：(1)Does the design really serve a human need?(2)Will it be competitive with existing products of rival companies?(3)Is it economical to produce?(4)Can it be readily maintained?(5)Will it sell and make a profit?Only time will provide the true answers to the preceding questions，but the product should be designed，manufactured and marketed only with initial affirmative answersThe design engineer also must communicate the finalized design to manufacturing through the use of detail and assembly drawingsQuite often，a problem will occur during the manufacturing cycleIt may be that a change is required in the dimensioning or tolerancing of a part 80 that it can be more readily producedThis falls in the category of engineering changes which must be approved by the design engineer so that the product function will not be adversely affectedIn other eases，a deficiency in the design may appear during assembly or testing just prior to shippingThese realities simply bear out the fact that design is a living processThere is always a better way to do it and the designer should constantly strive towards finding that better wayA new machine is born because there is a real or imagined need for itIt evolves from Someones conception of a device with which to accomplish a particular purposeFrom the conception follows a study of the arrangement of the parts，the location and length of links (which may include a kinematic study of the linkage)，the places for gears，bolts，springs，cams，and other elements of machinesWith all ideas subject to change and improvement，several solutions may be and usually are found，the seemingly best one being chosenThe actual practice of designing is applying a combination of scientific principles and a knowing judgment based on experienceIt is seldom that a design problem has only one right answer，a situation that is often annoying to the beginner in machine designEngineering practice usually requires compromisesCompetition may require a reluctant decision contrary to ones best engineering judgment；production difficulties may force a change of design；etcA good designer needs many attributes，for example：(1)A good background in strength of materials，SO that the stress analyses are soundThe parts of the machine should have adequate strength and rigidity, or other characteristics as needed(2)A good acquaintance with the properties of materials used in machines(3)A familiarity with the major characteristics and economics of various manufacturing processes，because the parts that make up the machine must be manufactured at a competitive costIt happens that a design that is economic for one manufacturing plant may not be so for another. For example，a plant with a well-developed welding department but no foundry might t5nd that welding IS the most economic fabricating method in a particular situation；whereas another plant faced with the same problem might decide upon casting because they have a foundry (and may or may not have a welding department) (4)A specialized knowledge in various circumstances，such as the properties of materials in corrosive atmospheres，at very low (cryogenic) temperatures，or at relatively high temperatures (5)A preparation for deciding wisely：(a)when to use manufacturers catalogs，buying stock or relatively available items，and when custom design is necessary；(b) when empirical design is justified；(C)when the design should be tested in service tests before manufacture starts；(d) when special measures should be taken to control vibration and sound (and others)(6)Some aesthetic sense，because the product must have ”customer appeal” if it is to sell (7)A knowledge of economics and comparative costs，because the best reason for the existence of engineers is that they save money for those who employ themAnything that increases the cost should be justified by, for instance，an improvement in performance，the addition of an attractive feature，or greater durability (8)Inventiveness and the creative instinct，most important of all for maximum effectivenessCreativeness may arise because an energetic mind is willing to actis dissatisfied with something as it is and this mind is willing to actNaturally, there are many other important considerations and a host of detailsWill the machine be safe to operate? Is the operator protected from his own mistakes and carelessness? Is vibration likely to cause trouble? Will the machine be too noisy? Is the assembly of the pans relatively simple? Will the machine be easy to service and repair?Of course，no one engineer is likely to have enough expert knowledge concerning the above attributes to make optimum decisions on every questionThe larger organizations will have specialists to perform certain functions，and smaller ones can employ consultants. Nevertheless, the more any one engineer knows about all phases of design, the better. Design is an exacting Profession，but highly fascinating when practiced against a broad background of knowledge译文机械设计概论机械设计是一门通过设计新产品或者改进老产品来满足人类需求的应用技术科学。它是一个广阔的工程技术领域，不仅要研究产品在尺寸、形状和详细结构等方面的基本构思，还要考虑产品在制造、销售和使用等方面的有关问题。 进行各种机械设计工作的人员通常被称为设计人员或者设计工程师。机械设计是一项创造性的工作。设计工程师不仅在工作上要有创新性，还必须在机械制图、运动学、动力学、工程材料、材料力学和机械制造工艺等方面具有深厚的基础知识。如前面所述，机械设计的目的是生产能够满足人类需求的产品。发明、发现和科学知识本身并不一定能给人类带来益处，只有当它们被用在产品上才能产生效益。因而，应该认识到在一个特定产品进行设计之前，必须先确定人们是否需要这种产品。应当把机械设计看成是设计人员运用创造性的才能进行产品设计、系统分析和制订产品的制造工艺的一个良机。掌握工程基础知识要比熟记一些数据和公式更为重要。仅仅使用数据和公式是不足以在一个好的设计中做出所需的全部决定。另一方面，应该认真精确地进行所有运算。例如，即使将一个小数点的位置放错，也会使正确的设计变成错误的。 一个好的设计人员应该勇于提出新的想法，而且愿意承担一定的风险，当新的方法不适用时，就恢复采用原来的方法。因此，设计人员必须要有耐心，因为所花费的时间和努力并不能保证带来成功。一个全新的设计，要求摒弃许多陈旧的，为人们所熟知的方法。由于许多人易于墨守成规，这样做并不是一件容易的事情。一位设计工程师应该不断地探索改进现有产品的办法，在此过程中应该认真选择原有的、经过验证的设计原理，将其与未经过验证的新观念结合起来。 新设计本身会有许多缺陷和未能预料的问题发生，只有当这些缺陷和问题被解决之后，才能体现出新产品的优越性。因此，一个性能优越的产品诞生的同时，也伴随着较高的风险。应该强调的是，如果设计本身不要求采用全新的方法，就没有必要仅仅为了变革的目的而采用新办法。 在设计的初始阶段，应该允许设计人员不受各种约束，充分发挥创造性。即使产生了许多不切合实际的想法，也会在设计的早期，即绘制生产图纸之前被改正掉。只有这样，才不致于堵塞创新的思路。通常要提出几套设计方案，然后加以比较。很有可能在最后选定的方案中，采用了某些未被接受的方案中的一些想法。 心理学家经常谈论如何使人们适应他们所操作的机器。设计人员的基本职责是努力使机器来适应人们。这并不是一项容易的工作，因为实际上并不存在着一个对所有人来说都是最优的操作范围和操作过程。 另一个应该被认识到的重要问题是，设计工程师必须能够同其他有关人员进行交流和沟通。在开始阶段，设计人员必须就初步设计同管理人员进行交流和沟通，并得到批准。这一般是通过口头讨论，草图和文字材料进行的。为了有效地进行交流，需要解决下列问题: (1)所要设计的这个产品是否真正为人们所需要? (2)此产品与其他公司的现有同类产品相比有无竞争能力? (3)生产这种产品是否经济? (4)产品的维修是否方便? (5)产品有无销路?是否可以盈利? 只有时间才能对上述问题给出正确的答案。但是，产品的设计、制造和销售只能在对上述问题的初步肯定答案的基础上进行。设计工程师还应该通过零件图和装配图，与制造部门一起对最终设计方案进行沟通。通常，在制造过程中会出现某个问题。可能会要求对某个零件尺寸或公差作一些更改，使零件的生产变得容易。但是，工程上的更改必须要经过设计人员批准，以保证不会损伤产品的功能。有时，在产品的装配时或者装箱外运前的试验中才发现设计中的某种缺陷。这些事例恰好说明了设计是一个动态过程。总是存在着更好的方法来完成设计工作，设计人员应该不断努力，寻找这些更好的方法。新机械产生于实际的或设想的需要。它来自于设计者为了达到某个具体目的而准备设计的机械设施的概念。根据这个概念，继续研究零件的布置，连接件的长度和位置(可能还要包括连杆的运动学研究)，齿轮、螺栓、弹簧、凸轮及其它机械零件的位置。通过修正和改进我们的想法，我们可能并通常可以找到几个解决方案，从中选择一个看起来最好的。 实际的设计活动是各种科学原理的综合应用，是基于已有经验的正确判断。设计问题很少只有一种正确的答案，这一点往往困扰着机械设计新手。 设计经常要向工程实际妥协，满足竞争需要而勉强做出的决定可能与人们最好的工程判断完全相反，生产制造的困难也会使我们不得不改变设计。 优秀的设计者应该具备许多基本素质，包括： (1)掌握材料力学方面的知识，以便能够进行充分的应力分析，使机械零件具有足够的强度、刚度及其它所需的特性。 (2)熟知机械所用材料的特性。 (3)熟悉各种制造工艺的特点及成本，因为组装机器的零件的制造成本必须具有竞争性。在一个工厂碰巧被证明为经济实用的设计方案，可能并不适用于另一个工厂。例如，有的工厂焊接部门很先进但却没有铸造部门。在这种特殊条件下，他们可能会认为焊接是最经济的制造手段，而对于那些有铸造部门(可能有也可能没有焊接部门)的工厂，面临同样的问题却可能会选择铸造。 (4)有关各种工作环境的专业知识。例如在腐蚀气体、低温或相对高温下材料的特性。 (5)精明决断的必要准备。要了解：(a)什么时间使用厂商目录、购买原料及相关物品，什么时候必须按用户的要求确定设计；(b)什么时候根据经验设计；(c)什么时候进行投产前的实验；(d)什么时候要采取特殊措施控制振动和噪声。 (6)一定的审美能力，以便产品销售时能够吸引顾客。 (7)要了解各种经济学和成本比较的知识，因为对雇主来说，雇佣工程师最主要的原因是他们能够为雇主节省费用。成本增加必须有充分的理由，例如，改进性能，增加吸引力，或使产品更经久耐用。 (8)本能的创造性，这是提高效率的最重要素质。创造性来源于不满现状，创造性使思想付诸实施。 当然，还有许多其它重要的因素和细节。例如，机器操作是否安全?操作者粗心意是否会不受到伤害?振动可能引起故障吗?机器的噪声很大吗?零件的装配比较简便吗?机器使用和维修容易吗? 当然，没有一个工程师能够具有上述那些基本素质所应有的充分的专业知识，对每一个问题做出最适宜的解答。大公司有各个行业的专家，小公司可以聘请顾问。但工程师对设计各方面的了解，总是越多越好。设计是一个吃力的行业，但只要具有丰富的知识，设计工作还是十分有趣的。