機械英漢翻譯-機械設計基礎(編輯修改稿)

　

【文章內容簡介】 neer 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 contr01 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 3 sensing that something is not right． The need is usually not evident at a11． 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 need is for cleaner air, the problem might be that of reducing the dust discharge from powerplant 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． We can regard the thing to be designed as something in a black box． 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 the reliability． There are many implied specifications which result either from the designer’s 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 designer’s freedom． and hence are a part of the implied specifications． A small plant， for instance， may not Own clodworking machinery． Knowing this, The designer selects other metalprocessing methods which can be performed in the plant． The labor skills available and the petitive 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 can not take place without both analysis and optimization because the system under design must be analyzed to determine whether the performance plies 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