外文资料
Introduction to Mechanical Design
Mechanical design is the application of science and technology to devise new or improved products for the purpose of satisfying human needs. It 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 product. People who perform the various functions of mechanical design are typically called designers, or design engineers. Mechanical design is basically a creative activity. However, 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 mechanical design is to produce a product which will serve a need for man. Inventions, discoveries and scientific knowledge by themselves do not necessarily benefit people; only if they are incorporated into a designed product will a benefit be derived. It should be recognized, therefore, that a human need must be identified before a particular product is designed. Mechanical 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 manufactured. It is important to understand the fundamentals of engineering rather than memorize mere facts and equations. There are no facts or equations which alone can be used to provide all the correct decisions required to produce a good design. On the other hand, any calculation made must be done with the utmost care and precision. For example, if a decimal point is misplaced, a otherwise acceptable design may mot function. Good designs require trying mew ideas and being willing to take a certain amount of risk, knowing that if the mew idea does not work the existing method can be
reinstated. Thus a designer must have patience, since there is no assurance of success for the time and effort expended. Creating a completely new design generally requires that many old and well-established methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques and attitudes. A design engineer should constantly search for ways to improve an existing product and must decide what old, proven concepts should be used and what new, untried ideas should be incorporated. New designs generally have “bugs” or unforeseen which must be worked out before the superior characteristics of the new designs can be enjoyed. Thus there is a chance for a superior product, but only at higher risk. It should be emphasized that, if a design does not warrant radical new methods, such methods should not be applied merely for the sake of change. During the beginning stages of design, creativity should be all
owed to flourish without a great number of constraints. Even though many impractical ideas may arise, it is usually easy to eliminate then in the early stages of design before firm details are required by manufacturing. In this way, Innovative ideas are not inhibited. Quite often, more than one design is developed, up to the point where they can be compared against each other. It 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 promise. Psychologists frequently talk about trying to fit people to the machines they operate. It is essentially the responsibility of the engineer to strive to fit machines to people. This is not an easy task, since there is really no average person for which certain operating dimensions and procedures are optimum. Another important point which should be recognized is that a design engineer must be able to communicate ideas to other people if they ate to be incorporated. Communicating the design to others is the final, vital step in the design process. Undoubtedly many great designs, inventions, and creative works have been lost to mankind simply because the originators were unable or unable or unwilling to explain their accomplishments to others. Presentation is a selling job. The engineer when
presenting a new solution to administrative, management, or supervisory persons, is attempting to sell or to prove to them that this solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the solution have been largely wasted. Basically, there ate only three means of communication available to us. These are the written, the oral, and the graphical forms. Therefore the successful engineer will be technically competent and versatile in all three forms of communication. A technically competent person who lacks ability in any one of these forms is severely handicapped. If ability in all three forms is lacking, no one will ever know how competent that person is! The competent engineer should not be afraid of the possibility of not succeeding in a presentation. In fact, occasional failure should be expected because failure or criticism seems to accompany every really creative idea. There is a great deal to learn from a failure, and the greatest gains ate obtained by those wiling to risk defeat. In the final analysis, the real failure would lie in decoding not to make the presentation at all. To 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、It is economical to profit? 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 answers. The design engineer also must communicate
the finalized design to manufacturing through the use of detail and assembly drawings. Quite often, a problem will occur during the manufacturing cycle. It may be that a exchange is required in the dimensioning or tolerancing of a part so that it can be more readily produced. This falls in the category of engineering changes which must be approved by the design engineer so that the product function will not be adversely affected. In other cases, a deficiency in the design may appear during assembly or
testing just prior to shipping. Engineering design is a systematic process by which solutions to the needs of humankind are obtained. The process is applied to problems (needs) of varying complexity. For example, mechanical engineers will use the design process to find an effective, efficient method to convert reciprocating motion to circular motion for the drive train in an internal combustion engine; electrical engineers will use the process to design electrical generating systems using falling water as the power source; and materials engineers use the process to design ablative materials which enable astronauts to safely the earth’s atmosphere. The vast majority of complex problems in today’s high technology society depend for solution not on a single engineering discipline, but on teams of engineers, scientists, environmentalists, economists, sociologists, and legal personnel. Solutions are not only dependent upon the appropriate applications of technology but also upon public sentiment, government regulations and political influence. As engineers we are empowered with the technical expertise to develop new and improved products and systems, but at the same time we must be increasingly aware of the impact of our actions on society and the environment in general and work conscientiously toward the best solution in view of all relevant factors. Design is the culmination of the engineering educational process; it is the salient feature that distinguishes engineering from other professions. A formal definition of engineering design is found in the curriculum guidelines of the Accreditation Board for Engineering and Technology (AENT). ABEN accredits curricula in engineering schools and derives its membership from the various engineering professional societies. Each accredited curriculum has a well-deigned design component which falls within the ABEN guideline. The ABEN statement on design reads as follows: Engineering design is the process of devising a system, component, or process to meet desired needs. It is a decision making process (often iterative ), in which the basic sciences, mathematic, and engineering sciences are applied to convert resources optimally to meet a stated objective. Among the fundamental elements of the design
process are the establishment of objectives and criteria, synthesis, analysis, construction, testing, and evaluation. The engineering design component of a curriculum must include most of the following features:
development of student creativity, use of open-ended problems, development and use of modern design theory mad methodology, formulation of design problem statements and specifications, consideration of alternative solutions, feasibility considerations, production processes, concurrent engineering design, and detailed system descriptions. Further, it is essential to include a variety of realistic constraints such as economic factors, safety, reliability, aesthetics, ethics, and social impact. If anything can be said about the last half of the twentieth century, it is that we have had an explosion of information. The amount of data that can be uncovered on most subjects is overwhelming. People in the upper levels of most organizations have assistants who condense most of the things that they must read, hear, or watch. When you begin a search for information, be prepared to scan many of your sources and document their location so that you can find them easily if the date subsequently appear to be important. Some of the sources that are available include the following: 1、 Exiting solutions. Much can be learned from the current status of solutions to a specific need if actual products can be located, studied and, in some cases, purchased for detailed analysis. An improved solution or an innovative new solution new solution cannot be found unless the existing solutions are thoroughly understood. 2、 Your library. Many universities have courses that teach you how to use your library. Such courses are easy when you compare them with those in chemistry and calculus, but their importance should not be underestimated. There are many sources in the library that can lead you to the information that you are seeking. You may find what you need in an index such as the Engineering Index. There are many other indexes that provide specialized information. The nature of your problem will direct which ones may be helpful to you. Don’t hesitate to ask for assistance from the librarian. You should use to advantage the computer databases found in libraries and often available through CD-ROM technology.
3、Professional organizations. The American Society of Mechanical Engineers is a technical society that will be of interest to students majoring in mechanical engineering. Each major in your college is associated with not one but often several such societies. The National Society of Professional Engineers is an organization that most engineering students well eventually join, as well as at least one technical society such as the society of manufacturing engineers, the American Society of civil engineers (ASCE), or any one of dozens that serve the technical interests of the host of specialties with which professional practices seem most closely associated. May engineers are members of several associations and societies. 4、Trade journals. They are published by the hundreds, usually specializing in certain classes of products and services. Money and economics are
part of engineering design and decision making. We live in a society that is based on economics and competition. It is no doubt true that many good ideas never get tried because they are deemed to be economically infeasible. Most of us have been aware of this condition in our daily lives. We started with our parents explaining why we could not have some item that we wanted because it cost too much. Likewise, we will not put some very desirable component into our designs because the value gained will not return enough profit in relation to its cost. Industry is continually looking for new products of all types. Some are desired because the current product is not competing well in the marketplace. Others are tried simply because it appears that people will buy them. How do manufacturers know that a new product will be popular? They seldom know with certainty. Statistics is an important consideration in market analysis. Most of you will find that probability and statistics are an integral part of your chosen engineering curriculum. The techniques of this area of mathematics allow us to make inferences about how large groups of people react based on the reactions of a few.
中文翻译 机械设计简介
机械设计是为了满足人类需要而制定出的新产品或者改进旧产品时对科学 与技术的应用。 它是工程技术的一个巨大领域,这个领域不仅关注原先这种产品 的尺寸，形状以及构造方式， 而且考虑涉及这种产品的制造，销售和使用的其 它各方面的因素。 进行机械设计的各种各功能的人们被通常叫为设计者或者设计工程师。 机 械设计基本上是一次创造活动。 然而， 除富有创新精神之外， 一位设计工程 师也必须在机械制图，运动学，力学，材料工程，材料强度和制造工艺有一定的 背景知识。 精确的说，机械设计的目的就是为了满足人们的需求。 发明，创造和科学 知识它们自己可能不能让人获益； 但是只要他们合并在一起并设计产品，其益 处就会被得到。因此，在一种特别的产品被设计之前，人的需求必须被鉴定，这 一点应该被认识到。 机械设计应被视为一个机会， 利用创新人才的设想设计一个产品， 分析系统， 然后就如何制造产品作出正确的判断。 对工程基础的理解而不是仅仅记住事实和 方程式，这一点是很重要的。 没有哪个事实或方程式能单独提供要求生产一种 好设计的全部的正确的决定。 另一方面， 任何计算必须得最大限度小心和精密。 例如，一个小数点放错，就有可能得不到所要设计得到的结果。 好的设计应该需要尝试新的方法并且愿意承担一定的风险， 知道如果新想法 不起作用， 这种现有的方法可能被重新使用。由于为了成功所付出的时间以及努 力是不能保证的， 因此一个设计者必须要有耐心。创
造一个完全新的设计一般要 求很多旧的以及被建立起来的方法来推动。 这并不容易因为很多人坚持旧的想法， 技术和态度。设计工程师要不断寻找方法，以改善现有的产品，并且决定哪些旧 的、已被证明的概念须要采纳，哪些新的、未曾尝试的想法应该被包刮进来。 在那些新设计的优势特性可以被享有之前,新设计一般有4)它能被比较容易的保持吗？ (5)它将能被出售并且赢利吗？ 只有时间能提供上述问题的正确的答案，但是产品应该被设计，只用最初肯
定的答案生产并且销售。 设计工程师也必须通过使用细节和装配图多沟通定稿设 计到生产。 经常， 一个问题将在生产的循环期间产生。这可能是在一个部分的定尺寸或 者加工过程中所要求一次交换， 以便它能够被更容易生产。这在被设计工程师批 准的工程变化的种类方面下降， 以便产品功能将不被相反影响。 在其他情况里， 在设计过程中的一种缺陷可能在装运之前的装配或检测测试期间出现。 工程设计是一个系统的过程， 其中的解决方案是为了满足人类需要而得到的。 进程是不同的复杂性的问题（需求）的应用。例如，机械工程师，将利用设计过 程中， 以找到一个有效率的方式转换成往复运动，在一个内部内燃机以圆周运动 来驱动列车;电气工程师在使用过程中，以设计电动发电机系统使用，水位下降 为能源;材料工程师使用过程中，以设计烧蚀材料，使宇航员平安返回地球的大 气层。 在今天的高科技社会,绝大多数的复杂问题赖以解决的方案不仅仅取决于单一的 工程学科，而且还取决于团队的工程师，科学家，环境学家，经济学家，社会学 家，法律人员。解决方案不仅取决于适当技术的应用而且还取决于公众情绪，政 府规章和政治影响力。 作为工程师，我们有权与技术专家发展和改进新的产品和 系统，但同时我们必须意识到我们行动的影响：对社会和环境的总体工作，认真 对待最好的解决办法，鉴于对所有的相关因素。 设计是经过工程教育的过程，这是区别其他工程专业的显著的特点。 它的一个正式的定义是：工程设计是有工程与技术评审委员会（ AENT ）的 指引下建立的 。 AENT 委派的课程，在工程学校和源于其成员来自各工程专业 社团。各派驻课程已有一套完善的设计部分，其中属于 ABEN 的指引。该 AENT 声明，对设计内容如下： 工程设计是，制订一个系统，组件的过程，以应付预期的需求。同时它也是 一个决策过程（通常迭代） ，其中基础科学，数学，科学和工程科学的应用转 换成资源，以最大限度地满足目标。其中基本要素的设计过程中，是设立目标和 标准，合成，分析，构造，测试和评价。工程设计组成的一个课程必须具有以下 大部分特点：发展学生的创造力，利用不限名额问题，开发和利用现代设计理论 的方法，配方设计问题，报表和规格，考虑其他的解决办法，可行性的考虑，生
产进程，并行工程设计，以及详细的系统说明。此外，它必须包括各种现实的制
约因素，如经济因素，安全性，可靠性，美学，伦理学和社会的影响。 关于最近二十世纪下半叶， 其最大的特点， 那就是： 我们处在一个资讯爆炸时代。 可发现的数据量大部分的科目是压倒性的。 在上级的大多数组织的人们已经帮助 凝聚在他们必须读，听，或看的大部分的事情。当你开始寻找资料，准备以浏览 你的许多消息来源，并记录其位置，如果有日期就能方便你能够轻松的找到。 一些消息的来源也可以包括以下几个方面： 1、飞离解决方案。在某些情况下，根据具体需要从目前的现状解决办法，如果 实际的产品可以研究，购买详细的分析，我们可以从中学到很多东西。一种改进 的解决办法或是一个崭新的解决方案均不能被找到， 除非现有的解决方案是彻底 的了解。 2、你的图书馆。许多大学有课程，教你如何使用你的图书馆。此类课程的目的 是很容易当你比较他们与那些在化学和微积分，但其重要性是不可低估的。在图 书馆有许多来源，这些来源可以把你带到你想要寻找的资料。你可以找到你所需 要的一个指标，如工程索引。还有很多其他的指标，提供专门的信息。你的问题 的性质，将直接哪些是可以帮助你。不要再犹豫向馆员请求帮助。你应该使用， 以图书馆建立的电脑数据库，而且往往可以通过光盘技术。 3、专业组织。美国机械工程师学会是一个技术性的社会，这将是学生感兴趣的 主修机械工程。 在你的大学里， 每项重大的项目往往都是几个社团一起协助的而 不是一个。国家专业工程师协会，是一个大多数工程系学生都想加入的组织，以 及技术协会如社会制造工程师，美国土木工程师协会（ASCE ） ，或任何一个几 十项服务技术东道国的利益的组织， 专业与专业的做法似乎有最密切联系在一起 的。 5 月工程师协会成员也是其它几个社团和协会的成员。 4、贸易杂志。公布这些数据是由数百个团体，这些团体通常是专门从事某些类 别的产品和服务。 金钱和经济学是工程设计与决策的一部分。我们生活在一个基 于经济及竞争的社会中。 毫无疑问确实有很多好的想法从来没有得到通过，是因 为他们被认为在经济上不可行。 我们大部分人已经意识到我们日常生活的这种状 况。 我们开始与我们的父母解释为什么我们不能有我们所希望的一些项目，因为 它的成本太高了。同样，我们将不会把一些非常可取的成分融入我们的设计中，
因为价值上涨将不会获得足够的利润，相对于其成本。 工业正不断寻求所有种类的新的产品。有些是可取的，因为在市场上目前的 产品不能与之相互竞争。 而其它的都试图简单
， 因为在它看来， 人们会购买他们。 制造商怎么知道一个新的产品将受欢迎呢？他们很少确定。 在市场分析中统计是 一项重要的考虑因素。你们中的大部分人会发觉： 概率统计是一个不可分割的组 成部分， 在你所选择的工程课程中。 该技术在本领域的数学， 使我们作出的推论： 对如何大群体的人的反应的基础上的反应数。