Slice coherence in a query-based architecture for 3D heterogeneous printing

doi:10.1016/j.cad.2016.02.005

Computer-Aided Design

Volumes 75–76, June 2016, Pages 27-38

https://doi.org/10.1016/j.cad.2016.02.005 Get rights and content

Highlights

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We explore 3D Voronoi-based heterogeneous printing.
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We utilize Euler loops to minimize non-extruding fast travels.
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The motion paths of consecutive slices are almost the same.
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The motion paths are not generated from scratch at every slice.
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Only 3 local cases can arise when updating the motion paths.

Abstract

We report on 3D printing of artifacts with a structured, inhomogeneous interior. The interior is decomposed into cells defined by a 3D Voronoi diagram and their sites. When printing such objects, most slices the printer deposits are topologically the same and change only locally in the interior. The slicing algorithm capitalizes on this coherence and minimizes print head moves that do not deposit material. This approach has been implemented on a client/server architecture that computes the slices on the geometry side. The slices are printed by fused deposition, and are communicated upon demand.

Graphical abstract

Introduction

Object properties and performance characteristics depend, to a large extent, on the structure of the object’s interior. For instance, the strength of polycrystalline material cannot be determined without information about the shape and orientation of the interior cells, and their material composition. The outer boundary of the object normally determines the geometry of the object and reflects intended functionality, but the functionality must be supported by appropriate interior structure. In particular, the structure of the interior determines properties such as density, elasticity, stiffness, fatigue, current flow, sound absorption, thermal conductivity, and other salient properties of the material.

In order to analyze and study these properties in detail, many researchers model the interior structures of the objects as an aggregation of cells. A cell structure based on Voronoi tessellation is one of the most popular approaches in these studies, since it can generate realistic homogeneous and heterogeneous structures in both 2D and 3D. In fact, Voronoi tessellations can be considered to subsume many types of cell decomposition where the Voronoi sites are arranged in a special way. For instance, when the sites lie on the vertices of a regular grid we obtain a regular subdivision into blocks. In the following we assume a general position site arrangement unless otherwise noted.

We consider representations in which the volume is partitioned into cells where each cell has an interior with specific geometric and/or material specifications. For example, a particular cell might be stipulated to have

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a particular strength in a given direction,
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or a particular regular geometric structure of a certain characteristic,
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or be a specific, homogeneous material, and so on.

We investigate a manufacturing approach in which cells are separated by a membrane structure, and the interior is fabricated using filament deposition equipment or other fabrication techniques that proceed in the usual layer-by-layer methodology. We restrict to manufacturing the membrane separating the cells of the object partition. Specifically, we assume a cell geometry defined by a 3D Voronoi partition of the interior. The Voronoi partition is defined by a set of interior points, the sites of the partition. The sites may be specified explicitly as part of the design. Each such point has attributes that are a description of the cell interior. The attributes are sufficient to unambiguously specify cell interior. Examples include stipulated material, homogeneously filling the cell; variable density material where the density at a point x in the cell might be a function of the distance of the point from the cells site; empty cells; and so on. Cells are therefore convex polyhedra, except for cells that share part of the exterior boundary of the object. The representation is implicit in the sense that the cell specification is given by the sites along with the outer geometry of the object.

We will describe how to manufacture the cell membrane throughout the interior. Our algorithm is incremental, exploiting the fact that many successive slices are topologically the same, and that slices that differ topologically often differ only locally. Those differences are characterized by only a few cases. More than that, the algorithm seeks to deposit each membrane layer such that, at no time, the head requires repositioning without depositing material, unless the external boundary requires it.

The remainder of the paper is structured as follows. After a review of the literature is presented in the next section, the algorithm for our proposed manufacturing paradigm is given in Section 3. The paradigm is evaluated with various experiments and the results are summarized in Section 4. The paper concludes with some remarks in Section 5.

Section snippets

Background

Voronoi based modeling is used in different fields of science and engineering for many applications. Material scientists employ Voronoi tessellations to model and simulate polycrystalline materials under different conditions to analyze their physical properties. In these simulations, each Voronoi cell corresponds to a crystalline cell in the aggregate and the cells form the basis of finite element models used to determine elastic and plastic behaviors of the so modeled materials [1].

Besides

Print setup

In our experiments, we have decoupled the link between the CAD file and the printer, bypassing the proprietary software that creates the STL file. We generate the printer (machine) code directly and drive the printer from a Raspberry micro-computer that requests the G-code for the STL slices one-by-one, when the printer is ready for the next slice. This setup, although for this paper unnecessary, was chosen in anticipation of future experiments in which the dialog between printer and CAD system

Experimental evaluation of the manufacturing paradigm

We evaluate the performance of the proposed manufacturing paradigm for 3D printers using a MakerBot Replicator 2X printer. The experimental set-up is illustrated in Fig. 7. The printer has two nozzle heads and is directly connected to a single-board computer (Raspberry Pi) through USB. The single-board computer operates as a server sending slice files to the printer upon request, the printer being the client for this interaction. In turn, the raspberry requests the slice files from the CAD

Discussion

The traditional approach of treating each slice as a separate structure ignores the fact that, in many cases, there is a high degree of similarity between consecutive slices, geometrically as well as topologically. This is trivially the case when the interior of the object printed is filled with a fixed pattern that has little functional significance. A structure derived from a 3D Voronoi diagram, on the other hand, has functional significance, as evidenced by the extensive literature on the

Acknowledgment

The project has been partially supported by the National Science Foundation, CMMI-1361783.

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View full text

Slice coherence in a query-based architecture for 3D heterogeneous printing

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Background

Print setup

Experimental evaluation of the manufacturing paradigm

Discussion

Acknowledgment

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An image analysis method to obtain the effective thermal conductivity of metallic foams via a redefined concept of shape factor

Appl Therm Eng

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Food Bioprocess Technol