3英文翻译(珩磨).doc

Fundamentals of Mechanical Design Mechanical design means the design of things and systems of a mechanical naturemachines, products, structures, devices, and instruments. For the most part mechanical design utilizes mathematics, the materials sciences, and the engineering-mechanics sciences.The total design process is of interest to us. How does it begin? Does the engineer simply sit down at his desk with a blank sheet of paper? And, as he jots down some ideas, what happens next? What factors influence or control the decisions which have to be made? Finally, then, how does this design process end?Sometimes, but not always, design begins when an engineer recognizes a need and decides to do something about it. Recognition of the need and phrasing it in so many words often constitute a highly creative act because the need may be only a vague discontent, a feeling of uneasiness, or a sensing that something is not right.The need is usually not evident at all. For example, the need to do something about a food-packaging machine may be indicated by the noise level, by the variation in package weight, and by slight but perceptible variations in the quality of the packaging or wrap.There is a distinct difference between the statement of the need and the identification of the problem which follows this statement. The problem is more specific. If the end is for cleaner air, the problem might be that of reducing the dust discharge from power-plant stacks, or reducing the quantity of irritants from automotive exhausts.Definition of the problem must include all the specifications for the thing that is to be designed. The specifications are the input and output quantities, the characteristics and dimensions of the space the thing must occupy and all the limitations on these quantities. In this case we must specify the inputs and outputs of the box together with their characteristics and limitations. The specifications define the cost, the number to be manufactured, the expected life, the range, the operating temperature, and t he reliability.There are many implied specifications which result either from the designers particular environment or from the nature of the problem itself. The manufacturing processes which are available, together with the facilities of a certain plant, constitute restrictions on a designers freedom, and hence are a part of the implied specifications. A small plant, for instance, may not own cold-working machinery. Knowing this, the designer selects other metal-processing methods which can be performed in the plant. The labor skills available and the competitive situation also constitute implied specifications.After the problem has been defined and a set of written and implied specifications has been obtained, the next step in design is the synthesis of an optimum solution. Now synthesis cannot take place without both analysis and optimization because the system under design must be analyzed to determine whether the performance complies with the specifications.The design is an iterative process in which we proceed through several steps, evaluate the results, and then return to an earlier phase of the procedure. Thus we may synthesize several components of a system, analyze and optimize them, and return to synthesis to see what effect this has on the remaining parts of the system. Both analysis and optimization require that we construct or devise abstract of the system which will admit some form of mathematical analysis. We call these models mathematical models. In creating them it is our hope that we can find one which will simulate the physical system very well.Evaluation is a significant phase of the total design process. Evaluation is the final proof of a successful design, which usually involves the testing of a prototype in the laboratory. Here we wish to discover if the design really satisfies the need or needs. Is it reliable? Will it compete successfully with similar products? Is it economical to manufacture and to use? Is it easily maintained and abjusted? Can a profit be made from its sale or use?Communicating the design to others if 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 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 are only t here 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, on 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 be learned from a failure, and the greatest gains are obtained by those willing to risk defeat. In the final analysis, the real failure would lie in deciding not to make the presentation at all.Machine 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 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 machine design are typically called designers, or design engineers. Machine design is basically a creative activity. However, in addition to being innovative, a design engineer must also have a soild 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 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.Good 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 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 mew, untried ideas should be incorporated.New 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 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 allowed to flourish without a great number of constraints. Even 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 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 design 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 are to be incorporated. Initially, the designer must communicate a preliminary design to get management approval. This is usually done by verbal discussions in conjunction with drawing layouts and written material. To communicate effectively, the following questions must be answered:Does the design really serve a human need?Will it be competitive with existing products of rival companies?Is it economical to produce?Can it be readily maintained?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 change is required in the dimensioning or telegramming of a part so that is 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. These realities simply bear out the fact that design is a living process. There is always a better way to do if and the designer should constantly strive towards finding that better way. 机械设计基础机械设计方法的设计和系统的机械性的东西,机器、产品结构、设备、工具. 在大多数情况下使用数学机械设计、材料科学与工程机械科学. 总设计过程关心我们. 如何开始? 请问工程师是在办公桌坐下空白纸? 并找到了他的一些想法,未来会出现什么情况? 什么因素影响或控制而被迫作出的决定. 最后,则是如何设计这个过程结束. 有时,但并不总是,设计工程师开始时,承认有必要做决定的时候了. 必须承认,它在重复这么多话往往是富有创造性的行为,因为可能需要在模糊的不满,感到不安,或感应到一些不正确的. 通常需要在所有并不明显. 举例来说,有必要做一些食品包装机可显示的音量,不同的方案重量,并略有差异,但明显的质量和包装容器. 有明显差别,需要说明的问题,确定了以下这一声明. 更具体的问题. 如果最后是清新空气,这个问题可能是从减少粉尘排放发电厂焚烧或减少汽车废气量从手腕. 问题的定义必须包括所有规格的事,是设计. 规格的投入和产出的数量、规模和特色的东西要占据空间的限制,所有这些数量. 在这种情况下,我们必须明确投入和产出的盒子连同其特点和局限性. 规格确定成本,多是生产、生活的期望、范围、经营温度t和他的可靠性. 这意味着有许多具体的结果是设计者的特定环境还是从自身的性质问题. 现有的制造工艺,与某工厂设施,构成限制设计师的自由,因此是一种隐含的规范. 小厂为例,本身并不冷工作机制. 知道这一点,设计师选择其他金属加工方法,可以在全厂进行. 现有的劳动技能和竞争力的具体情况,也是暗示. 在已确定的问题,并写了一套规范意味着获得,下一步是设计一个最佳的综合解决方案. 现在不能进行综合分析和优化,因为制度设计分析,以确定是否要执行符合规格. 设计是一个反复的过程中,我们通过几个步骤进行,评估结果,然后再回到早期阶段的程序. 因此,我们可以组成一个个综合系统,分析和优化,并返回综合效应看看这对系统的剩余部分. 分析和优化的要求,我们设计建造或抽象的系统,承认某种数学分析. 我们要求这些模型的数学模型. 他们建立的是,我们希望能找到一个模拟系统的实际很好. 评估是一个重要阶段,总的设计过程. 最后证明是评价设计成功了,通常都是在实验室测试样本. 在这里,我们发现,如果想真正满足需要或者设计的需要. 是否可靠? 是否与同类产品的竞争中脱颖而出? 这是经济生产和使用. 这是坚持和调整容易? 可以从销售利润取得或使用? 如果别人沟通设计最后,在设计过程中的重要一步. 毫无疑问,许多伟大的设计、发明、创作,已经失去了人类的原因不能或不愿解释别人的成就. 职业介绍是一个卖. 工程师,当提出一个新的解决行政、管理或监督人员,试图出售或向他们证明这种办法是比较好的. 如果能够这样做的成功,所花费的时间和努力得到解决,有相当大的浪费. 基本上,只有这里t为我们提供的通信手段. 这是书面、口头、图表和表格. 因此,成功的工程师将有能力和技术技能三种传播方式. 有技术专长的人,这些人没有任何形式的能力受到很大的限制. 如果有三种形