Shape Deposition Manufacturing

Solid Freeform Fabrication (SFF) processes " rapidly " create three dimensional shapes of arbitrary complex geometries by incremental material deposition of 2 1 / 2 dimensional layers. Automated planning and execution of the fabrication process is possible, and the need for part-specific tooling or fixturing is eliminated. However, there are inherent limitations in the resulting surface quality, due to the 2 1 / 2 D nature of the building process, and the current approaches are not capable of directly producing fully dense, well-bonded metal structures. Global economies and increasing competition require the fast and cost effective development of high quality products and rapid changes in design and functionality, demanding the rapid creation of functional parts, such as prototypes and tools for mass productions (e.g. injection molds). This thesis addresses the issue of rapidly and automatically fabricating functional metal parts directly from CAD models. A newly developed process called Shape Deposition Manufacturing (SDM) is introduced. The process is based on the concept of layered manufacturing in SFF, but uses separate deposition and shaping steps to create a layer. Three dimensionally shaped layers are created using 5-axis CNC machining, to achieve the required geometric accuracy for fully functional shapes. Thermal deposition technologies (thermal spraying, welding) are used to achieve the required material properties. A novel, droplet based deposition process, microcasting, has been developed, to create well-bonded, high-strength material, while minimizing the heat input into previously shaped layers. To create layers with a true three dimensional geometry, more detailed building strategies, than used by conventional SFF processes, are required by the SDM process. A CAD based planning system, which addresses these issues by decomposing a solid model of a part into layers and man-ufacturable, fully three dimensional segments is described. An automated testbed facility installed at Carnegie Mellon's Shape Deposition Laboratory is discussed, and shows the feasibility of automating the process. The microcasting process is explained in detail and it's performance in the SDM environment is evaluated. Different strategies and material combinations for the support structure have been developed and are presented with detailed descriptions of several building strategies for parts with various complexity and material quality. Material properties of structures created by the SDM process are evaluated. Problems affecting the accuracy and material integrity of SDM created structures, which mainly involve the buildup of thermal stresses during material deposition, are identified and opened for future research. Finally, various parts, with different complexity, …