What Are The Three Generations Of CAD?

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The first generation of CAD equipment, 2-D CAD, might be described as computerized drafting systems. The user can construct an image, add dimensions, reproduce symbols, and manipulate the image in ways impossible with pencil and paper. If the system is interactive, the image will respond instantly to every addition, change, or instruction.

This instantaneous exchange of information allows designers to create a design, with imagination and creativity unconstrained by bulky media such as pencil and paper. When the designer settles on a final version of the design, it is stored in a memory device such as a magnetic disk. Peripheral devices such as plotters, drafting systems and line printers will automatically generate any needed conventional drawings and documents commonly known as hard copy. But basically, computer graphics reduces traditional dependency on drawings and related paperwork, and in many cases, eliminates the need.

Computer graphics is having far-reaching affects precisely be-cause drawings, sketches, and related documents have always been so fundamental and important. Drawings and documents are the conventional means of communicating design information. Without a means to record and share decisions about what a product should look like and how it should be made, manufacturing would be impossible.

With 2-D CAD, the process of drawing and editing the drawings of parts, plans, or blueprints is streamlined. Says Josef Woodman, educational manager for AutoCAD, "There is no doubt that drafting tables will, over the next decade, be largely replaced by computers, much in the same way that typewriters as we know them will cease to exist. Computer-assisted design is not a passing fad. The technology saves money by allowing productivity ratios of up to 5:1 over conventional "board and pencil" techniques."

Clarence Burdette, Assistant Superintendent in the West Virginia educational system, agrees. "Image processing is as important in the industrial sciences," he says, "as word processing is in business."

The second generation of CAD equipment, also widely available commercially, is true 3-D CAD. These systems let the operator draw an image of a part, using either wireframe models or "surfacing"-a technique that displays the surface of objects.

A third generation of CAD equipment, available commercially but not used as widely, allows the operator not only to draw the object in three dimensions, but also to view the part realistically. Users can rotate, move, and view the part from any angle. In some cases, they can even derive characteristics of performance.

This "solids modeling" ability that 3-D CAD has helps designers and engineers to "construct" on the computer screen a sophisticated solid model of an object. One IBM plant uses this type of CAD system to design cabinet arrangements for IBM mainframe computers. It's even possible for the designer to "pull out a drawer" of the cabinet, to be sure it does not hit a cable-all this, on computer screen, before the product is ever physically built.

Such CAD systems, however, are extraordinarily complex, and re-quire a great deal of computing power. Generating an image of the computer cabinet from a different viewing angle, with all hidden lines removed, may take several minutes of computer processing time. The Office of Technology Assessment reports that when CAD is used for such mechanical purposes as the computer cabinet design at IBM, each model consists of a polyhedron with roughly 40,000 separate faces. The computer stores the faces, manipulates them, and determines whether or not they will be "hidden" on the screen, according to the CAD operator's instructions.

Another 3-D CAD system from turnkey vendor Tektronix allows CAD designers and engineers to call up output from tasks such as structural analysis and design, finite element modeling, or thermal vibration analysis, and to display them on the computer terminal.

Once an object is drawn, it can be rotated on horizontal, vertical, or depth axes. Then, using system controls for zoom, pan, and perspective, the operator can view the displayed part, vehicle, or system, seeing it just as he or she would see it in real life.

Systems that have true 3-D CAD capabilities have been popular with major industries, especially in the automotive field.

How Cad and Cam Fit Together

Ideally, computer-aided design (CAD) and computer-aided manufacturing (CAM) are parts of a broader concept, computer-integrated manufacturing (CIM).

The more sophisticated CAD systems can-and do-go beyond computer-aided drafting. CAD lets an operator or designer work out the physical dimensions of the product and the steps necessary to produce it on the computer. Through electronic communication, this information can be transmitted to computer-aided manufacturing equipment.

Some CAD systems let the operator "see" the machining process on the screen, and help to guide the operator through various steps in planning the machine process. The CAD system can produce a tape which can be fed into a machine tool controller and used to guide the machine tool path. Under conventional manufacturing processes, a manufacturing engineer would interpret design drawings and establish plans for the machine to make the required part.

In addition, sophisticated CAD systems are important components of computer-aided engineering (CAE). Of course the CAD system makes it easier to perform drafting and design changes. But engineers can use CAD systems to visualize how a product will work, or to get an estimate of its performance. Other computer graphics programs help engineers to perform finite element analysis.

The solids modeling ability of 3-D CAD systems, which lets the computer calculate and display such characteristics as the volume and density of the design being drawn, and the finite element analysis capability of such sophisticated systems make them extremely valuable engineering tools in major industries such as automobile manufacturing and aerospace. Since weight is a critical factor in the design of products in those industries, 3-D CAD systems are a basic part of the technology that lets engineers optimizes designs which use the least possible material, while still maintaining strength.
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