Design by composition for layered manufacturing

Three dimensional rapid prototyping processes, also called layered manufact uring or solid freeform fabrication (SFF) promise designers the ability to automatically fabricate complex shapes. SFF processes were invented with th e assumption that designers would submit complete part models for automated planning and manufacturing. This planning process is normally based on som e form of "decomposition, " for example, slicing into layers. Especially fo r newer, more complex SFF processes, there are several disadvantages to thi s approach, primarily that decomposition is difficult and does not reliably produce good process plans. Furthermore, it is hard for the designer to ge t feedback on the manufacturability of his design, and today's decompositio n systems are not fully automated. This paper presents an alternative appro ach, "design by composition," where users build designs from ''primitives'' that include high-level manufacturing plans. When the user combines two pr imitives with a Boolean operation, software will automatically generate a m anufacturing plan for the new design from the plans for the source primitiv es. In contrast to the decomposition method, design by composition offers s everal benefits to designers, primarily access to manufacturability feedbac k during design-time, a greater degree of automation, the ability to create designs with embedded components (such as sensors, electronic circuits, be arings, and shafts), and enhanced control over manufacturing plans. These a dvantages make design by composition a more attractive approach to SFF proc essing, especially for designers who are new to these processes. [S1050-047 2(00)01701-3].