Communications of the ACM
OpenFab: A Programmable Pipeline for Multimaterial Fabrication
Three rhinos defined and printed using OpenFab.
3D printing hardware is rapidly scaling up to output continuous mixtures of multiple materials at increasing resolution over ever larger print volumes. This poses an enormous computational challenge: large high-resolution prints comprise trillions of voxels and petabytes of data, and modeling and describing the input with spatially varying material mixtures at this scale are simply challenging. Existing 3D printing software is insufficient; in particular, most software is designed to support only a few million primitives, with discrete material choices per object. We present OpenFab, a programmable pipeline for synthesis of multimaterial 3D printed objects that is inspired by RenderMan and modern GPU pipelines. The pipeline supports procedural evaluation of geometric detail and material composition, using shader-like fablets, allowing models to be specified easily and efficiently. The pipeline is implemented in a streaming fashion: only a small fraction of the final volume is stored in memory, and output is fed to the printer with a little startup delay. We demonstrate it on a variety of multimaterial objects.
1. Introduction
State-of-the-art 3D printing hardware is capable of mixing many materials at up to 100s of dots per inch resolution, using technologies such as photopolymer phase-change inkjet technology. Each layer of the model is ultimately fed to the printer as a full-resolution bitmap where each "pixel" specifies a single material and all layers together define on the order of 108 voxels per cubic inch. This poses an enormous computational challenge as the resulting data is far too large to directly precompute and store; a single cubic foot at this resolution requires at least 1011 voxels and terabytes of storage. Even for small objects, the computation, memory, and storage demands are large.
At the same time, it is challenging for users to specify continuous multimaterial mixtures at high resolution. Current printer software is designed to process polygon meshes with a single material per object. This makes it impossible to provide a continuous gradation between multiple materials, an important capability of the underlying printer hardware that is essential to many advanced multimaterial applications (e.g., Wang et al.20). Similarly, there is no support for decoupling material from geometry definition and thus no ability to specify material templates that can be reused (e.g., repeating a pattern that defines a composite material, or defining a procedural gradation for functionally graded materials).
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