模具专业毕业设计外文翻译.doc

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1、本科毕业设计论文外文资料翻译Material Selection During recant years the selection of engineering materials has assumed great importance. Moreover, the process should be one of continual reevaluation. New materials often become available and there may be a decreasing availability of others. Concerns regarding envir

2、onmental pollution, recycling and worker health and safety often impose new constraints. The desire for weight reduction or energy savings may dictate the use of different materials. Pressures from domestic and foreign competition, increased serviceability requirements, and customer feedback may all

3、 promote materials reevaluation. The extent of product liability actions, often the result of improper material use, has had a marked impact; in addition, the interdependence between materials and their processing has become better recognized. The development of new processes often forces reevaluati

4、on of the materials being processed. Therefore, it is imperative that design and manufacturing engineers exercise considerable care in selecting, specifying, and utilizing materials if they are to achieve satisfactory results at reasonable cost and still assure quality. The first step in the manufac

5、ture of any product is design, which usually takes place in several distinct stages: (a) conceptual; (b) functional; (c) production design. During the conceptual-design stage, the designer is concerned primarily with the functions the product is to fulfill Usually several concepts are visualized and

6、 considered, and a decision is made either that the idea is not practical or that the idea is sound and one or more of the conceptual designs should be developed further. Here, the only concern for materials is that materials exist that can provide the desired property. If no such materials are avai

7、lable, consideration is given as to whether there is a reasonable prospect that new one could be developed within cost and time limitations. At the functional or engineering design stage, a practical, workable design is developed .Fairly complete drawings are made, and materials are selected and spe

8、cified for the various components. Often a prototype or working modal is made that can be tested to permit evaluation of the product as to function, reliability, appearance, serviceability, and so on. Although it is expected that such testing might show that some changes may have to be made in mater

9、ials before the product is advanced to the production-design stage, this should not be taken as an excuse for not doing a thorough job of material selection. Appearance, cost, and reliability factors should be considered in detail, together with the functional factors. There is much merit to the pra

10、ctice of one very successful company which requires that all prototypes be built with the same materials that will be used in production and, insofar as possible, with the same manufacturing techniques. It is of little value to have a perfectly functioning prototype that cannot be manufactured econo

11、mically in the expected sales volume, or one that is substantially different from what the production units will be in regard to quality and reliability. Also, it is much better for design engineers to do a complete job of material analysis, selection, and specification at the development stage of d

12、esign rather than to leave it to the production design stage, where changes may be made by others, possibly less knowledgeable about all of the functional aspects of the product. At the production design stage, the primary concern relative to materials should be that they are specified fully, that t

13、hey are compatible with, and can be processed economically by, existing equipment, and that they are readily available in the needed quantities. As manufacturing progresses, it is inevitable that situations will arise that may require modifications of the materials being used. Experience may reveal

14、that substitution of cheaper materials can be made. In most cases, however, changes are much more costly to make after manufacturing is in progress than before it starts. Good selection during the production design phase will eliminate the necessity for most of this type of change. The more common t

15、ype of change that occurs after manufacturing starts is the result of the availability of new materials. These, of course, present possibilities for cost reduction and improved performance. However, new materials must be evaluated very carefully to make sure that allTheir characteristics are well es

16、tablished. One should always remember that it is indeed rare that as much is known about the properties and reliability of a new material as about those of an existing one. A large proportion of product failure and product liability! Cases have resulted from new materials being substituted before th

17、eir long-term properties were really known. Product liability actions have made it imperative that designers and companies employ the very best procedures in selecting materials. The five most common faults in material selection have been: (a) failure to know and use the latest and best information

18、available about the materials utilized; (b) fail are to fore, and take into account the reasonable uses for the product( where possible, the designer is further advised to foresee and account for misuse of the product, as there have been many product liability cases in recent years where the claiman

19、t, injured during misuse of the product, has sued the manufacturer and won);(c) the use of materials about which there was insufficient or uncertain data, particularly as to its king term properties; (d) inadequate, and unverified, quality control procedures; and(e) material selection made by people

20、 who are complete unqualified to do so. The Computer in Design and Graphics Computers are widely used in engineering and related fields and their use is expected to grow even more rapidly than in the past Engineering and technology students must became computer literate, to understand the applicatio

21、ns of computer and their advantages. Not to do so well place students at a serious disadvantage in pursuing their careers. Computer-aided design (CAD) involves solving design problems with the help ofComputer: to make graphic images on paper with a plotter or printer, analyze design data, and store

22、design information for easy retrieval. Many CAD systems perform these functions in all integrated manner, greatly increasing the designers productivity. Computer-aided design drafting (CADD), an offshoot of CAD, is the process of Generating engineering drawings and other technical documents by compu

23、ter and is more directly related to drafting than is CAD. The CADD user inputs data by keyboard and/or mouse to produce illustrations on the monitor screen that can be reproduced as paper copies with a plotter or printer. Engineers generally agree that the computer does not change the nature of the

24、design process but is a significant tool that improves efficiency and productivity. The designer and the CAD system may be described as a design team: the designer provides knowledge, creativity, and control; the computer generates accurate, easily modifiable graphics, performs complex design analys

25、is at great speed, and stores and recalls design information. Occasionally, the computer may augment or replace many of the engineers other tools, but it cannot replace the design process, which is controlled by the designer. Depending on the nature of the problem and the sophistication of the compu

26、ter system, computers offer the designer or drafter some or all of the following advantages. 1. Easier creation and correction of drawings. Working drawings may be created more quickly than by hand and making changes and modifications is more efficient than correcting drawings made by hand. 2. Bette

27、r visualization of drawings. Many systems allow different views of the same object to be displayed and 3D pictorials to be rotated on the CRT screen. 3. Database of drawing aids. Creation and maintenance of design databases (libraries of designs) permits storing designs and symbols for easy recall a

28、nd application to the solution of new problems. 4. Quick and convenient design analysis the designer can evaluate alternative design thereby considering more possibility while speeding up the process at the same time. 5. Simulation and testing of designs. Some computer systems make possible the simu

29、lation of a products operation, testing the design under a variety of conditions and stresses; computer testing may improve on or replace construction of models and prototypes. 6. Increased accuracy. The computer is capable of producing drawings with more accuracy than is possible by hand; Many CAD

30、systems are even capable of detecting errors and informing the user of them. 7. Improved filing. Drawings can be more conveniently filed, retrieved, and transmitted on disks and tapes. Computer graphics has an almost limitless number of applications in engineering and other technical fields. Most gr

31、aphical solutions that are possible with a pencil can done on a computer and usually more productively. Applications vary from 3D modeling and finite element analysisi4 to 2D drawings and mathematical calculations.Once the domain of large computer systems advanced applications can now be done on mic

32、rocomputer. An important extension of CAD is its application to manufacturing. Computer-aided design/computer-aided manufacturing (CAD/CAM) systems may be used to design a part or product, devise the essential production steps, and electronically communicate this information to and control the opera

33、tion of manufacturing equipment, including robots. These systems offer many advantages over traditional design and manufacturing systems, including less design effort, more efficient material use, reduced lead times, greater accuracy, and improved inventory control. 材料选择 近些年来，工程材料的选择已经显得非常重要。此外，选择过程

34、应该足一个对材料的连续不断的重新评价过程。新材料不断出现，而一些原有的材料的可以被利用的数量可能会减少。环境污染、材料的吸收利用、工人的健康及平安等方面经常会对材料选择附加新的限制条件。为减轻重量或者和约能源，可能要求使用不同的材料、来自国内和国际的竞争、对产品维修保养方便性要求的提高和顾客的反应等方面的压力，都会促使人们对材料进行重新评价。由于材料选用不当造成的产品责任诉讼，已经产生深刻的影响此外，材料与材料加工之间的相互依赖关系已经被人们认识得更清楚。新的加工方法的出现，通常会促使人们对被加工材料进行重新评价。因此，为了能在合理的本钱和确保质量的前提下，获得满意的结果，设计工程师和制造工程

35、师都必须认真仔细地选择、确定和使用材料。 制造任何产品的第一步工作都是设汁。设计通常可以分为几个明确的阶段：(a)概念设计;(b)功能设计；(c)生产设计。在概念设计阶段，设计者着重考虑产品应该具有的功能。通常要设想和考虑几个方案，然后决定这种想法是否可行；如果可行，那么应该对其中一个或几个方案做进一步的改良。在此阶段，关于材料选择惟一需要考虑的问题是：是否有性能符合要求的材料可供选用；如果没有的话，是否有较大的把握在本钱和时间都允许的限度内研制出一种新材料。 在功能设计或工程设计阶段，要做出一个切实可行的设计。在这个阶段需要绘制相当完整的图纸，选择并确定各种零件的材料。通常要制造出样机或者实

36、物模型，并对其进行试验，评价产品的功能、可靠性、外观和维修保养性等。虽然这种试验可能说明，在产品进入生产阶段之前，应该更换某些材料，但是，绝对不能将这一点作为不认真选择材料的借口。应该结合产品的功能，认真仔细地考虑产品的外观、本钱和可靠性。一个很有成就的公司在制造所自样机时，所选用的材料应该和其在生产使用的材料相同并尽可能使用同样的制造技术。这样做，对公司是很有好处的。功能完备的样机如果不能根据预期的销售量经济地制造出来，或者样机与正式生产的装置在质量和可靠性方面有很大不同，那么这种样机就没有多大的价值。设计工程师最好能在这一阶段全部完成材料的分析、选择和确定工作，而不是将其留到生产设计阶段去

37、做。因为，在生产设计阶段材料的更换是由其他人进行的，这些人对产品的所有功能的了解可能不如设计工程师 在生产设计阶段中，与材料有关的主要问题是应该把材料完全确定下来，使它们与现有的设备相适应，能够利用现有设备经济地进行加工，而且材料的数量能够比拟容易地保证供给。在制造过程中，不可防止地会出现使用中的材料做一些更改的情况。经验说明，可以采用某些廉价材料作为替代品。然而，在大多数情况下，在进行生产以后改换材料比在开始生产前改换材料所花费的代价要高。在生产设计阶段做好材料选择工作，可以防止大多数的这种材料更换情况，在生产制造开始后出现了可供使用的新材料是更换材料的最常见的原因。当然，这些新材料可能降低

38、本钱、改良产品性能。但是，必须对新材料进行认真的评价，以确保其所有性能都被人们所了解。应当时刻牢记，新材料的性能和可靠性很少能像现有的材料那样为人们所了解。大局部的产品失效和产品责任事故案件是由于在选用新材料作为替代材料之前，没有真正了解它们的长期使用性能而引起的。 产品的责任诉讼迫使设计人员和公司在选择材料时，采用最好的程序。在材料选择过程中，五个最常见的问题为：(a)不了解或者未能利用关于材料应用的最新和最好的信息资料；(b)未能预见和考虑产品可能的合理用途(假设有可能，设计人员还应进一步预测和考虑由于产品使用方法不当造成的后果。在近年来的许多产品责任诉讼案件中，由于错误地使用产品而受到伤

39、害的原告控告生产厂家，并且赢得判决)；(c)所使用的材料的数据不全或者有些数据不确定，尤其当其长期性能数据是如此的时候；(d)质量控制方法不适当和未经验证；(e)由一些完全不称职的人员选择材料。 通过对上述五个问题的分析，可以得出这些问题是没有充分理由存在的结论对这些问题的分析和研究可以给防止这些问题的出现指明方向。尽管采用最好的材料选择方法也不能防止发生产品责任诉讼，设计人员和工业界按照适当的程序进行材料选择，可以大大减少诉讼的数量。从上面的讨论可以看出，选择材料的人们应该对材料的性质、特点和加工方法有一个全面而根本的了解。计算机在设计和制图中的应用 计算机在工程和相关领域内得到广泛的应用而

40、这种应用预计会得到越来越快的开展。工程技术专业的学生们应该通晓计算机了解计算机的用途干和它们的优点。不这样做，就会使学生们在将来的职业生涯中处于非常不利的地位。 计算机辅助设计(CAD)是应用计算机来帮助解决设计问题：这包括在视频显示器上生成图像，通过绘图仪或扣印机将这图像打印在纸上，分析试验数据，以便用检索的方式存储设计信息。许多CAD系统以集成的方式完成这些功能，极大地提高了设计人员的工作效率。 计算机辅助设计制图(CAD)是CAD的一个分支，它是通过计算机生成丁程图样和其他技术文件的过程。它与制图之间的关系要比CAD更多一些。CAD用户采用键盘和(或)鼠标输入数据以便在显示器屏幕上生成图

41、像。这些图像可以通过绘图仪或打印机输出到纸上。 工程师们通常认为计算机不会改变设计过程的性质 。 它只是一个能够显著提高工作效率和生产效率的工具，工作人员和CAD系统可以被视为是一个集体。设计人员提供知识、创造力和控制；计算生成准确并易于修改的图形，以很高的速度进行复杂的设计分析工作，以发存储和检索设汁信息。有时，计算机可对工程师所使用的许多其他工具起增强或替代作用，但是它不能取代由设计控制的设计过程。 根据设计问题的本质和所使用计算机系统的先进程度的不同对设计人员或制图人员来说，计算机可以有以下中的一些或全部优点。 1、易于绘制和修改图样。采用计算机可比用手工更快地绘制工作图。在图纸进行变更

42、和修改时，也比用手工完成效率更高。 2、对图样有更形象化的理解。许多系统可以显不同物体的不同视图，而且二维图像可以在阴极射线管(CRT)屏幕上旋转。 3、辅助制图数据库。建立和维护设计数据库(设计方案库可以存储设计方案和符号，以便于检索和用来解决新的难题。 4、快速和方便地进行设计分析。由于计算机可使分析变得容易，设计人员可对很多可供选择的设计方案进行评价。因此，在加快设计过程的同时，可以考虑更多的可能性 5、对设计进行仿真和检验。一些计算机系统可对产品的工作情况进行仿真，对在各种状况和应力作用下的设计方案进行检查。用计算机进行检验可以改良或者替代模型构造或样机。 6、提高精度。计算机能够绘制

43、出比手工绘制更为精确的图纸。许多CAD系统都能检测错误，且能将它通知用户。 7、改善档案管理工作。图纸可以更为方便地存档，检索和采用磁瓶或磁带传送。 计算机图形学在工程技术领域的应用几乎没有任何限制，大局部可以铅笔完成的图解方法都可以用计算机完成。且通常效率更高。其应用从建立三维模型和有限元分析，直到绘制平面图和进行数字计算。 许多曾经只能在大型计算机上运行的先进的应用软件，也可以在微型计算机上运行。CAD的一个重要的应用领域是制造业。计算机辅助设计/算机辅助制造(CADCAM)系统可以用来设计零件或产品，生成主要的生产工步，并且采用电子方式将此信息传给包括机器人在内的制造设备和控制它们的运行。与传统的制造系统相比，CADCAM系统有许多优点，包括减少设计工作量，提高材料利用率，缩短产品研制周期，提高精度和改善库存管理。