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Eklenme Tarihi: 23-11-08
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Dosya Açıklaması : 1.PRODUCTION DESIGN PROCESS What is design? If you search the literature for an answer to that question, you will find about as many definitions as there are designs. Perhaps the reason is that the process of design is such a common human experience. Websters dictionary says that to design is "to fashion after a plan," but that leaves out the essential fact that to design is to create something that has never been. Certainly an engineering designer practices design by that definition, but so does an artist, a sculptor, a composer, a playwright, or many another creative member of our society. Thus, although engineers are not the only people who design things, it is true that the professional practice of engineering is largely concerned with design; it is frequently said that design is the essence of engineering. To design is to pull together something new or arrange existing things in a new way to satisfy a recognized need of society. An elegant word for "pulling together" is synthesis. We shall adopt the following formal definition of design: "Design establishes and defines solutions to and pertinent structures for problems not solved before, or new solutions to problems which have previously been solved in a different way." Good design requires both analysis and synthesis. Typically we approach complex problems like design by decomposing the problem into manageable parts. Because we need to understand how the part will perform in service we must be able to calculate as much about the parts behavior as possible by using the appropriate disciplines of science and engineering science and the necessary computational tools. This is called analysis. It usually involves the simplification of the real world through models. Synthesis involves the identification of the design elements that will comprise the product, its decomposition into parts, and the combination of the part solutions into total workable systems. 1.1 Considerations of a Good Design Design is a multifaceted process. To gain a broader understanding of engineering design, we group various considerations in good design into three categories: (1) deign requirements, (2) life-cycle issues, and (3) regulatory issue. 1.1.1 Design Requirements It is obvious that to be satisfactory the design must demonstrate the required performance. Acceptable performance is the first, but far from only, design requirement. Performance measures both function and behavior of the design, i.e., how well the device does what it is designed to do. Performance requirements can be divided into functional performance requirements and complementary performance requirements. Functional requirements address such capacity measures as forces, strength, energy or material flows, power, and deflection. They are also concerned with the efficiency of the design, its accuracy and sensitivity. Complementary performance requirements are concerned with the useful life of the design, its robustness to factors in the service environment, its reliability, and ease, economy, and safety of maintenance. Issues such as built-in safety features and the noise level in operation must be considered. Finally, the design must conform to all legal requirements and design codes. A variety of analysis techniques must be employed in arriving at the features of a component in the design. By feature we mean specific physical attributes, such as shape, dimensions, or material properties. The digital computer has had a major impact in this area by providing powerful analytical tools based on finite-element analysis and finite difference. Calculations of stress, temperature, and other field-dependent variables can be made rather handily for complex geometry and loading conditions. When these analytical methods are coupled with interactive computer graphics, we have the exciting capability known as computer-aided engineering. Next to performance requirements we have physical requirements. These pertain to such issues as size, weight, shape, and surface finish. Environmental requirements deal with two aspects. The first concerns the service conditions under the product must operate. The extremes of temperature, humidity, corrosive conditions, dirt, vibration, noise, etc., must be predicted and allowed for in the design. The second aspect of environmental requirements pertains to how the product will behave with regard to maintaining a safe and clean environment, i.e., green design. Among these issues is the disposal of the product when it reaches its useful life. Aesthetic requirements refer to "the sense of the beautiful." They are concerned with how the product is perceived by a customer because of its shape, color, surface texture, and also such factors as balance, unity, and interest. This aspect of design usually is the responsibility of the industrial engineer, as contrasted with the engineering designer. The industrial designer is an applied artist. Decisions concerning the appearance of the product should be an integral part of the initial design concept. Manufacturing technology must be intimately connected with the product design. There may be restrictions on the manufacturing processes that can be used, because of either selection of material or availability of equipment within the company. The final major design requirements are cost. Every design has requirements of an economic nature. These include such issues as product development cost, initial product cost, life cycle product cost, tooling cost, and return on investment. In many cases cost is the most important design requirement, for if preliminary estimates of product cost look unfavorable, the design project may never be initiated. Cost enters into every ...