Design by Composition for Layered Manufacturing*

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Abstract
Three dimensional rapid prototyping processes, also called layered manufacturing or solid freeform fabrication (SFF), promise designers the ability to automatically fabricate complex shapes. SFF processes were invented with the assumption that designers would submit complete part models for automated planning and manufacturing. This planning process is normally based on some form of “decomposition,” for example, slicing into layers. Especially for newer, more complex SFF processes, there are several disadvantages to this approach, primarily that decomposition is difficult and does not reliably produce good process plans. Furthermore, it is hard for the designer to get feedback on the manufacturability of his design, and today’s decomposition systems are not fully automated. This paper presents an alternative approach, “design by composition,” where users build designs from “primitives” that include high-level manufacturing plans. When the user combines two primitives with a Boolean operation, software will automatically generate a manufacturing plan for the new design from the plans for the source primitives. In contrast to the decomposition method, design by composition offers several benefits to designers, primarily access to manufacturability feedback during design-time, a greater degree of automation, the ability to create designs with embedded components (such as sensors, electronic circuits, bearings, and shafts), and enhanced control over manufacturing plans. These advantages make design by composition a more attractive approach to SFF processing, especially for designers who are new to these processes. [S1050-0472(00)01701-3]