计算机辅助设计（CAD）及计算机辅助设计制造系统_中英文翻译.doc

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 various 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 usually 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 aid 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 system. 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 regard to one’s perspective, it will display all the object’s 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 geometric 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. F