1、附录 2：英文资料 Introduction to Mrchanical 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 pro
2、duct in terms of its size,shape and construction details,but also considers the various factors involved in the manufacture,markiong 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
3、 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,materialsengineering,strength of materials and manufacturing processes. As stated previously,the purpose of mechanical design is to
4、produce a product which will serve a need for man. Inventions,discoveries and scientific knowledge by themselves do not necessarily benfitpeople；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 be
5、fore 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
6、 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 calculations made must be done with the utmost care and precision. For example,if a dec
7、imal point is misplaced,an otherwise accrptable design may not function. 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 as
8、surance of success for the time and effort expended. Creating a completely new design generally requires that many old and wellestablished 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 way
9、s to improve an existing product and must decide what old,provenconcepts should be used and what new,untried should be incorporated. New design 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
10、 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 nu
11、mber 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 wher
12、e 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
13、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 engin
14、eer must be able to communicate ideas to other people if they are 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
15、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
16、, the time and effort spent on obtaining the solution have been largely wasted. Basically, there are only three means of communication available to us. There are the written, the oral, and the graphical firms. Therefore the successful engineer will be technically competent and versatile in all three
17、 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 successdin
18、g 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 learened form a failure, and the greatest gains are obtained by those willing to risk defeat. In the final analysis, the real f
19、ailure would lie in deciding 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) Is it economical to produce? (4) Can it be r
20、eadily 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 manufacturi
21、ng through the use of detail and assembly drawings. Quite often, a problem willoccurt during the manufacturing cycle. It may be that a change 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
22、 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
23、way to do it and the designer should constantly strive towards finding that better way. Some Rules for Mechanical Design Designing starts with a need, real or imagined. Existing apparatus may need improvements in durability, efficiently, weight, speed, or cost. New apparatus may be needed to perform
24、 a function previously done by men, such as computation, assembly, or servicing. With the objective wholly or partly defined, the next step in design is the conception of mechanisms and their arrangements that will perform the needed functions. For this, freehand sketching is of great value, not only as a record of ones thoughts and as an aid in discussion with others, but particularly for communication
