Representation and process planning for layered manufacturing of heterogeneous objects.

Conventional solid modeling systems have focused on developing homogeneous models of physical objects to capture their geometry and topology. These systems have thus far been sufficient since most physical objects found in engineering applications are homogeneous and manufacturing applications require us to deal primarily with their geometry. Two recent advances, structural optimization and layered manufacturing (LM) technologies, have brought to the forefront the need for CAD systems to support the design and fabrication of heterogeneous objects (such as multi-materials which have distinct material regions and functional graded materials (FGMs) which have continuous material composition (or microstructure) variation along with the geometry). This thesis describes the needs and components of such a CAD system. In particular, this thesis focuses on the development of a computational framework that is the missing link between the design and fabrication of heterogeneous objects. As part of this framework, a new representation scheme and a process planning method for LM of heterogeneous objects are developed. Several representation schemes (such as voxel-based, finite element-based, and decomposition-based models) have been proposed for heterogeneous objects. The limitations of these schemes are difficulties in model update and modification, and high storage cost. Based on the detailed assessment of these representation, a new representation, namely constructive representation of heterogeneous objects, is proposed. In particular, this new scheme focuses on the construction of complicated heterogeneous objects, guaranteeing desired material continuities at all the interfaces. In order to create various types of heterogeneous primitives, several methods for specifying material composition functions (such as geometry-independent, geometry-dependent functions, and multiple sets of these functions) are developed. Constructive Material Composition (CMC) and corresponding heterogeneous Boolean Operators (e.g., material union, difference, intersection, and partition) are then proposed to illustrate how material continuities are dealt with. LM methods such as Direct Metal Deposition (DMD), Shape Deposition Manufacturing (SDM), and Three Dimensional Printing (3DP) have capability to fabricate complete 3D heterogeneous objects by selectively depositing various materials on a point-wise fashion under computer control. To generate information for driving these LM machines, a new process planning method which takes into account the processing of material information, is proposed. The detailed tasks of this method are pre-processing (discretization), orientation (build direction selection), and adaptive slicing of heterogeneous objects. In particular, this thesis focuses on the discretization step which converts all material information inside an object into material features like geometric features, thus facilitating the build direction selection, adaptive slicing and tool path generation. Finally, an integrated prototype CAD system, which incorporates the Heterogeneous Solid Modeler (HSM) and synthesis tools for the synthesis of heterogeneous objects, is presented with a specific example. To verify the validity of the proposed method, a rectangular FGM part between Copper and Nickel was fabricated by a state of art technique using the DMD machine.PhDApplied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130555/2/3042169.pd