Computer-Aided Design and Manufacturing

• Author: Michel Mitri, Rhoda Wilburn
• Pages: 98-101

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Computer-aided design (CAD), also known as computer-aided design and drafting (CADD), involves the entire spectrum of drawing with the aid of a computer—from straight lines to custom animation. In practice, CAD refers to software for the design of engineering and architectural solutions, complete with two- and three-dimensional modeling capabilities.

Computer-aided manufacturing (CAM) involves the use of computers to aid in any manufacturing process, including flexible manufacturing and robotics. Often outputs from CAD systems serve as inputs to CAM systems. When these two systems work in conjunction, the result is called CADCAM, and becomes part of a firm's computer-integrated manufacturing (CIM) process.

CADCAM systems are intended to assist in many, if not all, of the steps of a typical product life cycle. The product life cycle involves a design phase and an implementation phase. The design phase includes identifying the design needs and specifications; performing a feasibility study, design documentation, evaluation, analysis, and optimization; and completing the design itself. The implementation phase includes process planning, production planning, quality control, packaging, marketing, and shipping.

CAD systems can help with most of the design phase processes, while CAM systems can help with

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most of the implementation processes. The contributions of CAD and CAM systems are described below.

CAD SYSTEMS

CAD systems are a specialized form of graphics software, and thus must adhere to basic principles of graphics programming. All graphics programs work in the context of a graphics device (e.g., a window on a monitor, a printer, or a plotter). Graphics images are drawn in relation to a 2-D or 3-D coordinate system, of which there are several types.

A device coordinate system is 2-D and maps images directly to the points (pixels) of the hardware device. In order to facilitate device-independent graphics, a virtual device coordinate system abstracts the 2-D points into a logical framework.

Of course, the devices being designed are generally 3-D objects, which also require a world coordinate system for representing the space in which the objects reside, and a model coordinate system for representing each of the objects in that space. CAD software includes algorithms for projecting the 3-D models onto the 2-D device coordinate systems and vice versa.

CAD systems include several primitive drawing functions, including lines, polygons, circles and arcs, rectangles, and other simple shapes. From these primitives, 3-D composites can be constructed, and include cubes, pyramids, cones, wedges, cylinders, and spheres. These shapes can be drawn in any color, and filled with solid colors or other patterns (called hatching). In addition, basic shapes can be altered by filleting (rounding) or chamfering (line segmentation).

Based on the manipulation of basic shapes, designers construct models of objects. A skeletal wire form model is a 3-D representation that shows all edges and features as lines. A more realistic-looking model is called a solid model, which is a 3-D model of the object being designed as a unitary whole showing no hidden features. The solid model represents a closed volume. It includes surface information and data determining if the closed volume contains other objects or features.

Solid modeling involves functions for creating 3-D shapes, combining shapes (via union, intersection, and difference operations), sweeping (translational and rotational) for converting simple shapes into more complex ones, skinning (for creation of surface...