Papers by Author: Khershed P. Cooper

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Authors: Khershed P. Cooper
Abstract: New manufacturing methods involving direct fabrication processes seem ideal for mass customization or “just-in-time” production. The use of tool-less means of production ensures reduced lead-time and lower cost. Besides, they provide flexibility in design and fabrication, which are essential for small lot sizes. However, part quality and production reliability are challenges that must be met. When adapted to the micro-factory paradigm, direct manufacturing can be made portable and capable of remote manufacturing. The benefits of miniaturization are savings in materials and energy consumption, but the increased surface area to volume ratio has implications for material behavior, especially mechanical strength. The newest incarnation of direct manufacturing is direct digital manufacturing or DDM, which involves localized deposition of material or energy and the creation of heterogeneous objects with digital means of control. DDM seeks spatial control of macrostructure, composition, texture and properties with the possibility of producing materials with unusual behavior, functionally gradient structures and integrated component devices. For DDM, multi-material design, precision in deposition, shaping and removal and understanding of heterogeneous material behavior are challenges.
Authors: Khershed P. Cooper, Samuel G. Lambrakos
Abstract: Additive manufacturing involves creating three-dimensional objects by depositing materials layer-by-layer. The freeform nature of the method permits the production of components with complex geometry. Deposition processes provide one more capability, which is the addition of multiple materials in a discrete manner to create “heterogeneous” objects with locally controlled composition. The result is direct digital manufacturing (DDM) by which dissimilar materials are added voxel-by-voxel (a voxel is volumetric pixel) following a predetermined tool-path. A typical example is functionally-graded material such as a gear with a tough core and a wear resistant surface. The inherent complexity of DDM processes is such that process modeling based on direct physics-based theory is difficult, especially due to a lack of temperature-dependent thermo-physical properties and particularly when dealing with melt-deposition processes. To overcome this difficulty the inverse problem approach is adopted to develop thermal models for multi-material, direct digital melt-deposition. This approach is based on the construction of a numerical-algorithmic framework for modeling anisotropic diffusivity such as that which would occur during energy deposition within a heterogeneous work-piece. This framework consists of path-weighted integral formulations of heat diffusion according to spatial variations in material composition and requires consideration of parameter sensitivity issues.
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