Representation of heterogeneous objects during design, processing and freeform-fabrication

Solid freeform fabrication (SFF) processes build parts layer-by-layer, starting from an electronic (CAD) representation of the part. Most commercial processes work with a single homogeneous material. However, new processes, such as shape deposition manufacturing (SDM), are able to handle heterogeneous materials with embedded components. To take full advantage of these processes, advances in both part representation and process planning are required. The orienting, supporting and subsequent decomposition of object geometry into simple entities (e.g. layers) is a fundamental milestone in SFF. Recognizing this milestone, and constructing an exchange representation around it, enables new design support and process planning tools that streamline the prototyping of complex, functional parts. We proposed a two-tier scheme, in which parts were mapped from a generic (or process-independent) representation, to an SFF-specific representation used for process planning. The generic representation encoded geometry and heterogeneous material attributes. The process-specific representation encoded the part orientation during fabrication, the decomposed part and support structure geometry, build sequence constraints and Boolean precedence properties (for combined operations), in addition to the geometry, material information and allowable variability in material attributes. We illustrated the use of these representations and the design tools they enable by demonstrating the design, process-planning and fabrication of a flexible multi-material link suitable for use as a robot leg.