外文翻译机械零件设计

外文翻译-机械零件设计 毕业设计(论文)译文 题目名称:机械零件设计 院系名称: 机械与动力工程学院 班 级: 机 制 04-2 学 号: 0403010216 学生姓名: 刘 伟 指导教师: 焦 锋 2008 年 5 月Design of Machine Elements ?( 原文 ) Fundamentally, design is the process of problem solving. Problem solving is used by professionals from many different fields in the normal course of their work .In this chapter, we will look at the definition of design and how it fits into the overall scheme of problem solving. We will also look at the process one uses in implementing a design task. We will then discuss the computational tools are helpful to the design analysis process. Finally, we will take a brief look at where one goes to acquire technical information to augment the design process.1-1 PROBLEM SOLVING AND DESIGN Engineering is defined by ABET the Accreditation Board for Engineering and Technology as: -that profession in which knowledge of the mathematical and natural sciences gained by study, experience and practice is applied with judgment to develop ways to utilize ,economically, the materials and forces of nature for the benefit of mankind. What differentiates engineering from many other fields is that it attempts to go from theory into practice for the purpose of developing products and processes instead of merely observing the phenomena of that science or art. For example ,a physicist studies and records findings in order to understand better some phenomenon or physical process. On the other hand , an engineer utilizes scientific information to make a particular process or product for use by consumers. ABET further defines the design portion of engineering activity 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 and mathematics 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 organization of problem solving is a hierarchical domain. One way to think of this is to consider the nested circles shown in Fig.I-1 below. What becomes obvious from this diagram is that many subfields are a part of the domain of problem solving .It is easy to think of problem solving that is not design because it is not oriented toward developing a product or process .For example ,when one solves a legal problem it is likely not design. In much the same way, one can follow the hierarchical structure to see that there are types of design that do not involve the use of engineering fundamentals .A good example of this would be interior design ,which draws heavily on art rather than on scientific or engineering knowledge .Within the domain of engineering design there are many subdomains that relate to the different disciplines of the engineering profession .In this text we are more interested in the discipline of mechanical engineering ,but it is safe to conclude that there are excellent design activities in other engineering fields such as electrical ,civil, chemical, etc. Figure I-1 The hierarchy of problem solving The smallest two domains presented in Fig I-1 are those of mechanical design and machine design .The reason for the distinction between these two is that the field of mechanical engineering is divided into two stems. These are the 1 energy stem and the 2 structures and motion stem .The term mechanical design applies to design in mechanical engineering systems where both stems can be involved .The field of machine design .however ,is a subset of mechanical design where the focus is on the structures and motion stem only .Thus , for example ,the design of heat exchangers ,air compressors ,and internal combustion engines involve mechanical design but are not machine design they rely on the use of technical material from heat transfer , thermodynamics , and combustion. These topic areas are all related to the energy stem of mechanical engineeringOn the other hand ,the design or a gear box ,a V-belt drive system ,a carburetor linkage ,or a machine strength of materials, solid body mechanics, kinematics , and dynamics .These technical materials are all related to the structures and motion stem of mechanical engineering .The topic of machine design is the focus of this text.1-2 THE DESIGN PROCESS It is important that a rational method of design be understood by engineers. There are two reasons for this. The first is that a rational method of design helps engineers to manage their task when confronted with a vast amount of input information .The second reason is that the use of a common procedure for design greatly facilitates interaction among engineers. Although the content of each engineering design problem is unique, the methodology for solving these problems is universal and be described in a specific way. Although a number of authorities on the methodology of design have presented descriptions of the process ,most of these descriptions tend to be similar. The design process, as we will describe it, involves the six-step procedure diagrammed in Fig.I-2.We will now look at the activity that takes place during each of these steps. Step 1: Recognize the need ?Some people mistakenly believe that engineers create need. This is ,of course ,no more true than the notion that physicians create illness or farmers create hunger. The products and processes created by engineering design are a direct response to specific needs of society .The first step in the design process is probably the single most important part of the overall process. Yet it is frequently given inadequate treatment in the design process .A carefully formulated statement of need can often save considerable time and energy later in the design cycle. Implied in any statement of need is an understanding of the real constraints on the problem. Once a statement of need has been established ,the designer would be well advised to review this statement periodically during the design process so that it can be revised if necessary. Step 2: Create a design ?Once the need has been clearly recognized and stated in a succinct way,the next step is to begin creating design ideas that will satisfy this need.Of all of the steps in the design process ,this one requires the most ingenuity and imagination. Step 3: Prepare a model ?Once an idea has been created ,it becomes necessary to find a means to evaluate the quality of that idea in satisfying the need requirements. One way to do this , of course , would be to build the suggested design ideaThis procedure is usually impractical for reasons of cost , time ,and effort. In order to conserve cost , time, and effort, engineers frequently make use of a simplified model to evaluate a design ideaA model may be real or abstract and may be anything from a simple mental image of the idea to a complex mathematical or physical reproduction of the proposed concept. A frequently used model is a mathematical equation that describes the physical performance of the part .Much of this book will be devoted to developing such mathematical relationships.A designer must understand that all models are only approximations of a physical phenomenon .It is thus important to know when a model is robust enough to give meaningful results. An understanding of significant figures in calculations is also highly important to performing design analysis. Step 4: Test and evaluate the model?Once the model has been prepared ,it is time to evaluate the proposed design idea by exercising the modelThe testing usually involves judgment .In the case of a mathematical model of a physical phenomenon , the engineer will put values into the equations and look at the resultsWhat becomes obvious as a result of this type of model is that it is important for the designer to become proficient in the manipulation of mathematical models and that a good system of documenting the solution process is highly desirable .It is for this reason that this book makes use of spreadsheet calculations to solve problems in machine.Figure I-2 The six-step process of design Step 5: Improve the design?As a result of the tests performed on the model. the engineer should have a quantitative measure of the success or failure of the idea. The engineer will likely know whether the ideas should be abandoned or whether it should be retained for further improvement .One of the fortunate results of testing and evaluation is that this process often provides considerable insight into where improvements can and should be made. Thus ,this step leads back to the creation step .Since a number of different design ideas may be tried, modified, and improved before a final design choice is made ,the process shown in Fig.I-2 is quite iterative. What is important to realize is that the design process may yield many workable solutions or no solutions at all .This characteristic is one that makes design problem solving quite different from most engineering science problems ,where there is often only one right answer Step 6: Communicate the design?No matter know well a design may satisfy a particular human need , it cannot be converted into a useful product or process if the details of the design are not communicated to those who will implement its use. Thus , the communication step is a very important part of the design process. Communication of engineering design ideas may be by written words ,spoken words ,or by pictures, graphs ,or drawings.As we think about applying the engineering design method diagram ,several important facts are worth keeping in mind .First , the human mind is capable of handling straightforward design decisions with remarkable speed .The complete process of making a good design choice need not take excessive time for routine problems. Second , the human mind often has difficulty defining boundaries between the steps in the process .The designer may combine one or more of the blocks in the diagram into what seems like a single activity .While this procedure is not wrong ,it should be avoided if it results in inadequate treatment of each important step.1-3 STAGES OF DESIGN The design process ,as described in the previous section ,is a thought module that can be applied over and over again in engineering practice .In the industrial environment ,design is frequently accomplished through a progressive series of four operational stages .These stages carry the design through from inception to completion .Each of these stages involves a complete design cycle .The four stages are presented in Fig.I-3 .Each of these stages is connected in series with the next so that the communications output of the first stage will provide a statement of need for the second stage and so on .The diagram also provides for the possibility of returning to a previous stage if the outcome of a particular stage suggests that this prudent .A close inspection of Fig.I-3 shows that the stage are :”feasibility stage,” ”preliminary stage,” detail stage,” and “revision stage .”The characteristics of each of these stages will now be discussed FigureI-3 The four stages of design Stage 1: Feasibility stage?The first stage determines it is both possible and profitable to undertake a given engineering project .For this reason ,the need statement will often be phrased “ to consider the desirability of -” or “ to consider the economic feasibility of -” The ideas generated during this stage of the design process generally consist of general statements about overall concepts rather than specific descriptions of hardware .The models for this stage tent to be based on economic theories ,market surveys ,and the opinions of authorities .For this reason ,people who are experts from disciplines other than engineering are often part of the design team during this stage .The output of this stage will generally be a recommendation either to proceed or to abandon the project. Stage 2: Preliminary stage?The purpose of the preliminary stage is to make qualitative judgments about the types of components and resources to use in meeting the conceptual need identified by the feasibility study .The statement of need for this stage usually calls for the designer to select the kinds of components that will be used to make the process or product .The selection process involves studying the tradeoffs between alternative types of component hardware and raw materials .It is beyond the scope of this stage to select quantitative things such as dimensional size ,critical geometry ,color ,weight ,etc. Stage 3: Detail stage?The communication output of the preliminary stage will form the basis for a statement of need that requires the complete ,detailed specification of the elements recommended for the final product or process .This is called the detail stage .The task required for the completion of this stage of design will involve making quantitative design selections with respect to size ,shape ,orientation ,color ,etc .The modeling and testing parts of this stage often involve extensive calculations and experimentsMuch of what we will develop in this text will be appropriate to making decisions in the detail design stage .The output of this stage usually results in the manufacture of the product. Stage 4: Revision stage?Once the detail stage has been completed and the product or process has been placed in service, it may be found desirable to use field experience as a basis for further improvement of the product .This process is called the revision stage .Since the final product is available , it often becomes the model for evaluation during the revision stage .The revision stage is not always used in the design process.出处:Design of Machine Elements:(英文版?原书第7版)/(美)斯波茨 Spotts,M.F.,(美) 舒普 Shoup,T.E. 著. ?北京:机械工业出版社,2002.8.(时代教育?国外高校优秀教材精选) ISBN 7-111-10751-9 机械零件设计 ? 译 文) 从根本上说,设计就是一个解决问题的过程。在日常工作过程中,专业人员在许许多多不同的领域都会用到这一方法。在这一章中,我们将会了解到设计的内涵以及它怎样用于解决问题的全过程。我们也将会具体看到一个人用其完成一项设计任务的过程。而后我们再讨论对设计分析过程来说,好的计算方法是十分有用的。最后,我们通过一个例子说明从哪获取技术信息以扩充其设计。1-1 问题解决及设计 工程技术认证委员会把工程定义为:那种通过学习研究获取数学和自然科学知识、经验、实践的专业,同时慎重的用其朝着经济利用大自然资源又对人类有益的方向发展。 是什么把工程从诸多领域中区分开来的呢?是因为它能成功的为开发产品而把理论变为现实的,而不是像其他科学或艺术,仅仅关注表面现象。例如,一个物理学家研究并记录发现结果,以便更好地理解一些现象或物理过程。然而,一个工程师会运用科技信息为消费者做一个特别处理或设计制作一种产品。工程技术认证委员会进一步定义工程活动的设计部分如下:图 I-1 问题解决的层次性 工程设计是这样一个过程,它为满足某种需要设计一系统、部件或者工艺处理。它是一个反复做决定的过程,这一过程是基于把科技、数学、工程科学用于为满足已定目标而做最佳的资源转换。设计过程中的基本单元由目标、标准、合成、分析、构造、测试以及评估构成。 这一问题解决组织属一层次性范畴。一种看法认为它系图I-1所示的嵌套性的。问题解决领域中的许多部分把这一图表变得更加清晰。很容易想到问题的解决不是一种设计,因为它不是面向产品或者过程的开发。例如,当一个人解决一法定的问题时,他不会以设计的方法去解决。同样的在许多方面,一个遵从这一结构的人会看到有许多设计类型并不包含这种工程基础的运用。一个很好的例子就是室内设计,它的绘画重点在艺术上,而不在科学或者工程知识上。在工程设计领域中有许多具有不同优势的内容,它涉及到工程职业的不同学科。在这一章中,我们着重点在于机械工程这一学科,然而会可靠的得出这样的结论,在其他工程领域内也有许多优秀的设计,比如电力工程,民用工程,化学工程等等。 在图示I-1中最小的两个部分是机械设计和机器设计。这两部分之所以有区别,是因为机械工程分了两个分支。机械设计术语在包含机械工程两个分支的系统中都有应用。机器设计领域是机械设计的一部分,它仅重在结构和运动杆件的设计。举个例子来说,热交换机、空气压缩机、内燃机的设计包含有机械设计,但不是机器设计,它运用到热交换,热力学,燃烧学等材料技术。这些主要区域涉及到机械工程的能量部分。另一方面,以下这些设计,齿轮箱,V型皮带驱动系统,化油器连接,或材料的机械力,稳定机身力学,运动学,动力学等。这些技术材料都会涉及到机械工程中的结构和运动问题。机器设计就是这章的重点。1-2 设计过程 一个合理的设计方法能否被工程师理解是很重要的。对于这一点来说,有两个原因:第一个就是面对大量的输入信息,工程师能够在这一合理设计方法帮助下顺利完成它们的任务;第二个原因就是使用这一普通设计能够极大便利工程师相互交流。尽管每个工程设计的内容都是唯一的,但是解决这些问题的方法有通用性,并会由一特别的方式加以描述。尽管有很多权威机构在设计方法上都曾对这一过程加以描述,但都大同小异,十分相似。我们描述这一设计工程时,可以用以下图解方法,可以被图解为六步过程。我们来看一下在每一步骤中发生的活动。 第一步:认知需求?有一些人错误的认为是工程师们创造了需求。当然,这比医生们创造了疾病和农民们创造了饥饿同样的不真实。产品或者某一过程被工程设计者创造,那是对社会特别需求的直接回复。在整个设计过程中的第一步可能是整个过程的最为重要的部分。然而,它在整个设计过程中往往给与不适当的处理。慎重的提出需求报告,往往能在后续的设计中节省可观的时间和精力。需求报告中的任意一点暗示都是对在问题中真正限制的一种理解。一旦需求报表确立,设计者就会被派去,在整个设计过程中周期性的进行考察,以便在其确实需要修改的情况下及时得到修正。 第二步:创立设计?一旦这一需求被清晰的找出并用一种简明的方法确立,下一步就要开始创立能够满足这种需求的想法。在所有设计过程的步骤中,这一步需要最多的灵感和想象力。 第三步:制备一个模型?一但方案创立出来,就有必要寻找一种方法去评估这种方案对需求满足的质量。当然,一种方法可以这样做,就是构建这种设计思想假设。这一过程通常由于费用,时间,精力的原因而显得不切合实际。为了节约时间,费用以及精力,工程师们通常用一种简化的模型去评估这种方案。一个模可以是真实或抽象的,也可以是