Modelling of multi-material assemblies for layered manufacturing

Abstract

Parts produced by all current Rapid Prototyping (RP) systems are made of a single material. A new system that can produce assemblies composed of parts with more than one colour or with more than one material is being developed so that some post-processing of RP parts, e.g., assembly and bonding can be removed. This research investigates the methodology to represent and produce multimaterial (MM) assemblies for RP. The work addresses three problems: modelling of MM assemblies, direct slicing and RP tool path planning of MM assemblies. Modelling MM assemblies is the first procedure in rapid manufacturing MM assemblies. An original MM assembly model for rapid manufacture is proposed. A graph model is used to organize all components in an assembly with different material properties by their boundary mating information in a non-manifold (NM) representation. Local mating information is also explicitly represented. Slicing operations can then be performed directly on the model. The model is applicable to cases of MM assemblies, inhomogeneous parts and single material assemblies. In order to eliminate the intermediate triangulation approximation process for curved boundary, a dexel encoding approach for direct slicing MM assemblies in RP is developed. Compared to other adaptive slicing approaches, double adaptive refinement is employed to provide better surface finish and accuracy. After slicing a MM assembly, there will be 2D regions of heterogeneous materials. In order to fill all material regions in a slice efficiently, they will be filled simultaneously by the tool holders. Collision-free path plan is to be generated to avoid interference between tool holders. A dexel-based path planning approach is proposed to detect collision. The longest first scheduling approach is used basing on 2D regions in dexel representation, which needs only simple computation. As a result, tool holders can fill the MM regions simultaneously and efficiently.