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repair, upgrade, and disposal. Such a comprehensive system will not be possible for many years.

However, an important first step toward this vision can be achieved by joining detailed design with manufacturing and assembly. To accomplish this requires a new level of information structuring and integration. Feature-based design is the best way currently known to capture and integrate the necessary information that links the geometry of parts with their functions, fabrication, and assembly. Present computer-aided design (CAD)1 systems support creation of geometry only. Apart from stress and thermal analyses of parts and certain types of kinematic analyses, most design analyses must be done manually because there is no way to obtain the necessary information from the circles and lines stored in the CAD system.

An IPPD system that realizes this first step toward a more comprehensive system will consist of three elements: a database, a set of algorithms, and user interfaces. The database will be structured to capture the information about the design in the form of geometry plus features (places of interest on each part, together with information on what role they play in the product's function and how to make and assemble the features in relation to each other). The algorithms will take the information they need from this database to simulate function, determine optimal assembly sequences, estimate fabrication or assembly cost, or perform design-for-assembly analyses, for example. The user interfaces will make it easier for the designer to create a design using features and apply the algorithms to study and perfect the design.

Prototype software that does some of these things exists now. This software can be a basis on which to build a new kind of computer-assisted design that integrates technical, business, and economic issues relevant to design. It can support analyses of cost and function, as well as the study of families of products that share parts or subassemblies. Such software has been demonstrated for the design of certain complex electro-mechanical items.

Another IT-enabled connection between design and manufacturing is the use of stereolithography as a visualization aid for designers and as the basis for rapid generation of prototype molds and dies for the production of mechanical parts. In an experiment conducted by a major automobile manufacturer, vendor bids based on a drawing and a stereolithographed model were lower than bids based on a drawing alone; this result was explained by the fabricator's greater ability to visualize the complexities of the item in question and thus to more accurately determine the costs of its fabrication.

1 Over the years, the acronym CAD has evolved in meaning. CAD initially stood for "computer-aided drafting"; however, perhaps because information technology achieved greater penetration into the world of design engineers, it has come to mean "computer-aided design," of which one part is drafting.

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