Feature-based design for heterogeneous objects - Mechanical ...

X. Qian, D. Dutta / Computer-Aided Design 36 (2004) 1263–1278 1269processes involving different materials. The three featuresprovide a generic tool for heterogeneous object modeling.Many existing design/fabrication automation tools forheterogeneous objects processing are dedicated tools andthey can be directly derived from these three synthesizedfeatures. For example, the feature operation semantics usedin design by composition for layered manufacturing [3] andMEMS fabrication process simulation [5] can all be derivedfrom the synthesized features [20].Based on these synthesized feature operations, a featurebased design methodology has been developed for heterogeneousobject design [20]. In our implementation, weadopted the R-m set as the working representation schemefor heterogeneous objects, even though other representationschemes can also be used to represent the semantic featuresdefined above. That is, in our implementation, an R-m setðg; mÞ is used as the building block for the constructivedesign. A compound feature (building block), consisting ofmore than one R-m set, can also be defined, i.e. a finitecollection of R-m sets, ðg 1 ; m 1 Þ; ðg 2 ; m 2 Þ; …; ðg n ; m n Þ; eachconsisting of a material volume. To support a constructivedesign of heterogeneous objects, we extended the radialedgegraph to represent the geometry of heterogeneousobjects [24]. In this extended data structure, each region hasits material composition representation and each face usehas neighborhood information, which contains a pointerpointing to material representation. Such a methodologyneeds two enabling component techniques: how to definematerial composition within each material volume and howto combine material volumes. These two enabling techniquesare presented in Sections 4 and 5.Fig. 7. Generic feature operations for heterogeneous objects.The partition feature functions the same as additivefeatures over the intersection region ðg 1 > g 2 Þ; but it is notapplicable to the region outside of g 1 : This partition featureis used extensively for heterogeneous object modeling whenmaterial functions are imposed on a given geometrydomain.These synthesized features support both form feature andmaterial feature operations. It associates each materialvolume with one geometric/material operator. They precluderedundant definitions of the geometry in both formfeatures and material features. The four types of relationshipsbetween the geometric volumes of form features andmaterial features can be fully manifested by the synthesizedfeatures in a constructive approach. In this approach, thebuilding blocks are the synthesized features. The designerhas two choices: either use the default materials to modelform features and then partition the part volume withspecific material composition functions, or glue a set ofmaterial feature volumes.These synthesized feature operations can be used todesign heterogeneous objects or simulate manufacturing4. Material heterogeneity modeling basedon design intentIn order to use synthetic material features as a buildingblock for feature based design, we need a method to definematerial heterogeneity within each feature volume that canrepresent design intents. During the iterative design editingprocess, these design intents need to be preserved. In thissection, we present a method in which designer specifymaterial variation within a feature volume throughdesigners’ intuition and experience.We use a B-spline tensor solid to represent a synthesizedmaterial feature volume. We use a virtual diffusion processto create material heterogeneity profile. The design intentsare represented as a set of constraints. The detailedmathematical formulation is available in Refs. [20,22,23].Solving diffusion equations under these constraints willautomatically ensure the material variation is smooth withineach material volume. In order to make this paper selfcontained,we briefly present the material heterogeneitymodeling method here, with emphasis on how design intentscan be represented and preserved within a feature during theediting process.