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TECHNICAL PAPERS

Thin-Wall Calculation for Layered Manufacturing

[+] Author and Article Information
Sara McMains

Mechanical Engineering Department, University of California, Berkeley, Berkeley, CA 94720-1740 ASME Member

Jordan Smith

Carlo Séquin

Computer Science Division, University of California, Berkeley, Berkeley, CA 94720-1776

J. Comput. Inf. Sci. Eng 3(3), 210-218 (Sep 16, 2003) (9 pages) doi:10.1115/1.1604812 History: Received March 01, 2003; Accepted June 01, 2003; Online September 16, 2003
Copyright © 2003 by ASME
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References

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STRATASYS, INC ., 1999, QuickSlice 6.2, Eden Prairie, MN.
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Kim,  D.-S., Hwang,  P. K., and Park,  B.-J., 1995, “Representing the Voronoi Diagram of a Simple Polygon Using Rational Quadratic Bezier Curves,” Comput.-Aided Des., 27(8), pp. 605–614.
Shewchuk,  J. R., 1997, “Adaptive Precision Floating-Point Arithmetic and Fast Robust Geometric Predicates,” Discrete Comput. Geom., 18(3), pp. 305–363.
McMains, S., Séquin, C., and Smith, J., 1998, “SIF: A Solid Interchange Format for Rapid Prototyping,” in Proceedings of the 31st CIRP International Seminar on Manufacturing Systems, CIRP, pp. 40–45.
McMains, S., 1999, The SIF_SFF Page. http://www.cs.berkeley.edu/∼ug/sif_2_0/SIF_SFF.shtml.
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Figures

Grahic Jump Location
For a simple rectangular block, all of the interior slices are “hidden” and thus can be built using the fast build style pictured on the left. For contrast, the regular solid-fill build style used on the top and bottom slices is pictured on the right, with densely spaced parallel roads in the interior. In areas where a part surface shows a shallow slope with respect to the build plane, the build style on the left cannot be used.
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Gaps result in a part built with an over-aggressive manual extension of the QuickSlice software’s fast build region
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For this central slice, the area we want to fill densely with the build material (a solid fill) is simply the slice offset region (Region1). The interior region of this layer will be filled with a looser cross-hatched pattern for support.
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We use a solid fill in the slices directly above or below horizontal faces (subset of Region2)
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We also use a solid fill at angled faces anywhere the current slice is not covered by the slice above or not covered by the slice below (subset of Region2)
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Here we are looking at a cross-section of the part. All of the regions that are in the slice offset regions are labeled with Region1 shading. The regions that were in Region2 but not Region1 are labeled with Region2 shading. The “gaps” in the thin wall are circled.
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Looking at the same cross section, we see the additional areas that are solid filled when we add Region3
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For a wall that we want to be two layers thick, we must extend Region2 up an additional layer above down faces and down an additional layer below up faces
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The cross section of the full 2-layer thick wall, showing the addition of the extended Region3+
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An example where it is necessary to clip the extended Region3+ against the boundary of the current slice
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Input contour (thick black), Voronoi diagram (thin gray), and offset contour (thick gray)
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Input contour in z=0 (thick black), Voronoi mountain (thin gray), and offset contour in z=d (thick gray)
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Input contours (thick black) and Voronoi diagram (thin gray)
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Input contours (thick black), Voronoi diagram (thin gray), and three inner and two outer offset contours (thick gray)
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The screw part manufactured using our algorithm. Using the QuickSlice software directly, the build took over twice as long to complete.
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A sample slice through the screw part, using the QuickSlice software’s fast build option. All of the interior roads are densely spaced. (The looser spaced roads on the exterior are for support material.)
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The same slice using our algorithm. The interior roads are loosely filled for a faster build.
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Detail of the cow tail region half way through the build

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