1、46 Computer-Aided Design and ManufacturingComputer-aided design（CAD）involves the use of computers to create design drawings and product models. Computer-aided design is usually associated with interactive computer graphics（known as a CAD system）. Computer-aided design systems are powerful tools and

2、are used in the mechanical design and geometric modeling of products and components.In CAD，the drawing board is replaced by electronic input and output devices. When using a CAD system，the designer can conceptualize the object to be designed more easily on the Graphics screen and can consider altern

3、ative designs or modify a particular design quickly to meet the necessary design requirements or changes. The designer can then subject the design to a variety of engineering analyses and can identify potential problems （such as an excessive load or deflection）.The speed and accuracy of such analyse

4、s far surpass what is available from traditional methods.46 Computer-Aided Design and ManufacturingDraft productivity rises dramatically. When something is drawn once，it never has to be drawn again. it can be retrieved from a library ,and can be duplicated, stretched, sized, and changed in many ways

5、 without having to be redrawn。Cut and paste techniques are used as labor-saving aids.CAD makes possible multiview 2D drawings ，and the drawings can be reproduced in different levels of reduction and enlargement. It gives the mechanical engineer the ability to magnify even the smallest of components

6、to ascertain if assembled components fit properly. Parts with different characteristics，such as movable or stationary ，can be assigned different colors on the display. Designers have even more freedom with the advent of 3-D parts and manipulate them in endless variations to achieve the desired resul

7、ts. Through finite element analysis ，stresses can be applied to be a computer model and the results graphically displayed，giving the designer quick feedback on any inherent problems in a design before the creation of a physical prototype.46 Computer-Aided Design and Manufacturing In addition to the

8、designs geometric and dimensional features，other information （such as a list of materials，specification ，and manufacturing instructions）is stored in the CAD database. Using such information ,the designer can then analyze the economics of alternative designs. Computer-aided manufacturing(CAM) involve

9、s the uses of computers and computer technology to assist in all the phases of manufacturing a product，including process and production planning，machining，scheduling，management ，and quality control. Computer-aided design and computer-aided manufacturing are often combined into CAD/CAM systems.This c

10、ombination allow the transfer of information from the design stage into the stage of of planning for the manufacture of a product，without the need to reenter the data on part geometry manually. The database developed during CAD is stored； then it is processed further，by CAM，into the necessary data a

11、nd instructions for operating and controlling production machinery，material-handling equipment，and automated testing and inspection for product quality. 46 Computer-Aided Design and ManufacturingIn machining operations，an important feature of CAD/CAM is its capability to describe the tool path for v

12、arious operations，such as NC turning，milling，and drilling. The instructions （programs）are computer generated，and they can be modified by the programmer to optimize the tool path .The engineer or technician can then display and visually check the tool path for possible tool collisions with fixtures o

13、r other interferences. The tool path can be modified at any time，to accommodate other part shapes to be machined.Some typical applications of CAD/CAM are：（a）programming for NC，CNC，and industrial robots；（b）design of tools and fixtures and EDM electodes；（c）quality control and inspection，for instance，c

14、oordinate-measuring machines programmed on a CAD/CAM workstation；（d）process planning and scheduling ；and（e）plant layout.46 Computer-Aided Design and Manufacturing. The emergence of CAD/CAM has had a major impact on manufacturing，by standardizing product development and by reducing design effort，tryout，and prototype work；it has made possible significantly reduced costs and improved productivity. The two-engine Boeing 777 passenger airplane，for example, was