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Research Papers

Manufacturability Feedback and Model Correction for Additive Manufacturing

[+] Author and Article Information
Saigopal Nelaturi

System Sciences Laboratory,
Palo Alto Research Center,
Palo Alto, CA 94304
e-mail: saigopal.nelaturi@parc.com

Walter Kim, Tolga Kurtoglu

System Sciences Laboratory,
Palo Alto Research Center,
Palo Alto, CA 94304

A regularized set is the topological closure of the set’s interior. Regularization is required to automatically merge disjoint but overlapping components in a slice, if they exist. Overlapping components create nonmanifold points, which are known to cause problems while simulating tool paths because it is difficult to distinguish points inside and outside the slice.

It is straightforward to identify holes in a polygonal boundary representation of a slice, by simply computing the winding number of the loops constituting various segments of a boundary.

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received April 15, 2014; final manuscript received December 5, 2014; published online February 4, 2015. Assoc. Editor: Darrell Wallace.

J. Manuf. Sci. Eng 137(2), 021015 (Apr 01, 2015) (9 pages) Paper No: MANU-14-1193; doi: 10.1115/1.4029374 History: Received April 15, 2014; Revised December 05, 2014; Online February 04, 2015

Additive manufacturing, or 3D printing, is the process of building three-dimensional solid shapes by accumulating material laid out in sectional layers. Additive manufacturing has been recognized for enabling production of complex custom parts that are difficult to manufacture otherwise. However, the dependence on build orientation and physical limitations of printing processes invariably lead to geometric deviations between manufactured and designed shapes that are usually evaluated after manufacture. In this paper, we formalize the measurement of such deviations in terms of a printability map that simulates the printing process and partitions each printed layer into disjoint regions with distinct local measures of size. We show that manufacturing capabilities, such as printing resolution, and material specific design recommendations, such as minimal feature sizes, may be coupled in the printability map to evaluate expected deviations before manufacture. Furthermore, we demonstrate how partitions with size measures below required resolutions may be modified using properties of the medial axis transform and use the corrected printability map to construct a representation of the manufactured model. We conclude by discussing several applications of the printability map for additive manufacturing.

Copyright © 2015 by ASME
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Figures

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Fig. 1

An asymmetrical bracket for which the printability map is shown in Fig. 5

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Fig. 2

The as-manufactured model for the bracket shown in Fig. 1 constructed using printability maps

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Fig. 3

Medial axis depicted as the locus of centers of maximally inscribed circles (left) and as nondifferentiable points on the distance function (right) [17]

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Fig. 4

A representation of a family of sets O(S,k2B) − O(S,k1B), k1 − k2 = 1. Each set in the family represents the region that cannot be printed without scaling down the structuring element k1B to a smaller k2B. The largest k1B has a radius of max(τ(x)),x ∈ MS.

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Fig. 5

Printability map for a single layer of the model shown in Fig. 1. Disjoint regions of the printability map are indicated to represent regions with local size below the smallest printable feature (at thin walls and rings), regions with local size larger than the smallest printable feature but below recommended thickness (adjoining the thin walls and rings), and all other regions with local size greater than recommended thickness.

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Fig. 6

3D printed cats printed with increasing layer thickness

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Fig. 7

Cat model visualized with varying layer thicknesses (from left to right 0.1 mm, 0.2 mm, and 0.4 mm). Regions below printer resolution and recommended thickness are highlighted.

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Fig. 8

Reconstruction of a floral shape (middle) from a tool path (left) and the corresponding printability map (right) with a structural element larger than the print head

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Fig. 9

The types of contact possible for end points of the medial axis transform [17]

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Fig. 10

The pruned medial axis transform of the slice shown in Fig. 5. The distance to the boundary of the slice is visualized as a map on the medial axis.

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Fig. 11

Model correction at thin walls and protrusions below the recommended feature size

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Fig. 12

Model correction at bridges below the recommended feature size

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Fig. 13

Local thickening causes topological change by unifying disjoint components into a connected set

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Fig. 14

Automatic model correction retains topology but changes form. (Left) the regions of the model below recommended local size. (Middle) the model with its medial axis transform. (Right) model correction by local thickening covers one hole and splits the other into two, thereby retaining topological equivalence with the original shape.

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Fig. 15

The medial axis of bounded sets in the complement of the slice

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Fig. 16

Voronoi diagram of the segments defining the input slice. Notice that the discretization of curved edges into line segments creates a dense distribution of medial axis edges.

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Fig. 17

Voronoi diagram pruned to remove medial axis edges that terminate at an input vertex

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Fig. 18

Edges from the pruned medial axis are filtered and the resulting set consists of all medial edges whose transform at every point is less than the minimum local size

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Fig. 19

Medial edges from Fig. 18 are dilated by the required local size

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Fig. 20

The difference between the dilated medial edges and the original slice shows additional material required to meet the specified minimum feature size

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Fig. 21

As-manufactured bracket from Fig. 1 with model correction shown highlighted. Note that model correction is not attempted at sharp corners which will get rounded during the printing process. Computation time for two slices is shown in Table 2

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Fig. 22

As-manufactured bracelet with model correction shown highlighted. Computation time for two slices is shown in Table 2.

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