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TECHNICAL PAPERS

Design by Composition for Layered Manufacturing*

[+] Author and Article Information
Mike Binnard, Mark R. Cutkosky

Center for Design Research, Stanford University, Stanford, CA 94305

J. Mech. Des 122(1), 91-101 (Jan 01, 1999) (11 pages) doi:10.1115/1.533549 History: Revised January 01, 1999; Received July 01, 1999
Copyright © 2000 by ASME
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References

Figures

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When the designer combines two primitives (left), the merging algorithms combine the manufacturing plans (right) to produce a plan for the new design. In this example, the plans are represented by cross sectional views of regions of part material encapsulated in support material that will subsequently be etched or melted away. The composition algorithms preserve ordering constraints among the various regions.
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Shading used in illustrations
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The SDM process cycle. Material is alternately deposited and shaped by different processes. This methodology permits selecting a deposition process that gives good material quality and a shaping process that has good tolerances and surface finish.
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As an alternative to the decomposition of previously generated CAD models, design by composition simplifies process planning and permits immediate analysis of evolving designs.
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Cross-sections of a primitive and its compact set. The compact set (b) for the primitive (a) contains two part material compacts and three support material compacts. The external surfaces of the compact set are either the top or bottom of the workspace, W, or parallel to the growth axis.
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Compact-set merging algorithm. The first part of the algorithm creates the intersection compacts. The function f() is specified by the truth tables shown in Fig. 7. The second part puts nonintersecting compacts into the result set.
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Truth tables for compact set merging operations. The tables specify the material type (part or support) for a compact, c=f(a,b), which is formed by the intersection of two source compacts, a and b.
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An example merging operation. Two primitives, A and B, are combined with a union operation. The amount of overlap between them is determined by their position in the CAD workspace.
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A simple design by composition example. The designer wants to combine the two primitives in (a) to form the shape in (b).
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The two compact sets that will be combined
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Step 1 of the merging operation. The two compacts in (a) are intersected, producing the intersection compact in (b). The intersection is subtracted from the two source compact sets (c), and is added to the result set, C, in (d).
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Steps 2 and 9 of the merging operation. In step 2, the remaining piece of compact a1 is intersected with compact b2. In step 9, the remainder of compact a3 is intersected with b3.
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Source and result CPGs for the example in Fig. 9. The algorithms described in Section 5.1 create the precedence links in the result CPG based on the two source CPGs.
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The compact graph in (a) can be simplified in different ways; two of the possibilities are shown in (b) and (c).
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CPG simplification algorithm. This algorithm uses a utility function calculation to rank all possible simplification alternatives.
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CAD model of embedded components for a robot leg and sequence of merged compacts for creating the leg. The top layer of support material is a product of the merge algorithm in Section 4 and is not required for manufacturing.
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Close-up view of leg (a) just after inserting pneumatic components (step 5 in Fig. 16) and view of finished part (b).
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Integrating design by composition and decomposition. The bold arrows represent transmission of compact graphs.

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