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1、 附录:英文资料及翻译Computer-Aided Design CAD A CAD system is basically a design tool in which the computer is used to analyze various aspects of a designed product. The CAD system supports the design process at all levels?conceptual, preliminary, and final design. The design can then test the product in var
2、ious environmental conditions, such as temperature changes, or under different mechanical stress. Although CAD systems do not necessarily involve computer graphics, the display of the designed object on a screen is one of the most valuable features of CAD systems. The picture of the object is usuall
3、y displayed on the surface of cathode-ray tube CRTputer graphics enables the designer to study the object by rotating it on the computer screen, separating it into segments, enlarging a specific portion of the object in order to observe it in detail, and studying the motion of mechanisms with the ai
4、d of programs. Most CAD systems are using interactive graphics system. Interactive graphics allows the user to interact directly with the computer in order to generate manipulate, and modify graphic displays. Interactive graphics has become a valuable tool, if not a necessary prerequisite, of CAD sy
5、stem. The end products of many CAD systems are drawing generated on a plotter interfaced with the computer. One of the most difficult problems in CAD drawing is the elimination of hidden lines. The computer produces the drawing as wire frame diagram. Since the computer defines the object without reg
6、ard to ones perspective, it will display all the objects surfaces, regardless of whether they are located on the side facing the viewer or on the back, which normally the eye cannot see. Various methods are used to generate the drawing of the part on the computer screen. One method is to use a geome
7、tric modeling approach, in which fundamental shapes and basic elements are used to build the drawing. The lengths and radii of the elements can be modified. For example, a cylinder is a basic element, the subtraction of a cylinder with a specific radius and length will create hole in the displayed p
8、art. Each variation, however, maintains the overall geometry of the part. Other CAD systems use group technology in the design of parts. Group technology is a method of coding and grouping parts on the basis of similarities in function or structure or in the ways they are produced. Application of gr
9、oup technology can enable a company to reduce the number of parts in use and to make the production of parts and their movement in the plant efficient. Recently CAD systems are using the finite-element method FEM of stress analysis. By this approach the object to be analyzed is represented by a mode
10、l consisting of small elements, each of which has stress and deflection characteristics. The analysis requires the simultaneous solution of many equations; a task which is performed by the computer, the deflections of the object can be displayed on the computer screen by generating animation of the
11、model. With any of these methods, or other which are used, the CAD system generates at the design stage a single geometric data base which can be used in all phases of the design and later in the manufacturing, assemble, and inspection processes.CAD/CAM Systems Computer-aided design CAD means the us
12、e of a computer to assist in the design of an individual part or a system, such as an aircraft. The design process usually involves computer graphics. Computer-aided manufacturing CAM means the use of a computer to assist in the manufacture of a part. CAM can be divided into two main classes: 1 On-l
13、ine applications, namely, the use of the computer to control manufacturing systems in real time, such as CNC and AC systems of machine tools. 2 Off-line applications, namely the use of the computer in production planning and non-real-time assistance in the manufacturing of parts. CAD/CAM is a unifie
14、d software system, in which the CAD portion is interfaced inside the computer with the CAM system. The end result of current CAD/CAM systems is usually a part program in the form of a list or punched tape. In advanced CAD/CAM systems part programs can be directly fed into the control computers of CN
15、C machines and inspection stations. The main concept of CAD/CAM systems is the generating of a common database which is used for all the design and manufacturing activities. These include specifications of the product, conceptual design, final design, drafting, manufacturing, and inspection. At each
16、 stage of this process, data can be added, modified, used, and distributed over networks of terminals and computers. The single database provides a substantial reduction in human errors and a significant shortening of the time required form the introduction of a concept of a product to the manufacturing of the final physical product. The size and capability of the required computer system depend on the complexity
