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EETE OCT 2015

3D design exploration before print By Julien Happich 3D printing is taking over the world, it seems, but so far non-CAD users are only left with catalogue parts to choose from. Modifying an existing 3D digital file can be painstaking for the non-initiated, and even for experts, the tedious process could turn a good product design into a non-printable part or something that would lack the structural integrity of the original design. Hence, typical 3D printing houses and file repositories only offer proven printable products with very little room for customization. Yes, you can probably tick some boxes to choose the material or the colour, sometimes there is room to carve out some text, but any other modification would in essence mean a redesign and performing a battery of 3D-printability checks, at your own risks. Researchers at MIT and the Interdisciplinary Center Herzliya in Israel have come up with a browser-based user interface that lets anyone modify and quickly visualize a whole new design space around an original 3D part, while doing all the necessary checks (printability, structural analysis) in the background. In a paper titled “Fab Forms: Customizable Objects for Fabrication with Validity and Geometry Caching”, MIT graduate student in computer science and engineering Masha Shugrina details how she leverages cloud computing to pre-qualify parametric design variations for manufacturability based on adaptive sampling of the design space. For each original 3D design, the authors perform a precomputation of the modified object by varying the general design parameters and then prune off the non-printable or structurally non-viable results from the exploration space. For practical purposes, only a few parameters are left visible to the online users who can interactively sweep a small set of parameters through different values using virtual sliders (the other hidden parameters will be swept based on their geometric ties with the visible parameters). The precomputation stage means that the results are displayed in real time rather than minutes or even hours, rendering the 3D object as a valid proposition regardless of the slider’s position, ready to print. In their examples, the team distributed the precomputations over 10 to 40 custom cores on Amazon Web Services, and distributed sampling took less than a day for most models. Adaptive sampling was required to generate more samples where geometry is changing the most, so that end-users get the impression of continuously changing the parameters as they manipulate the sliders. So would commercial companies or CAD library companies have to deliver a particular file format for the MIT Fab Forms algorithms to elaborate all the possible (and printable) sample variations, and how would a CAD part provider chose which parameters are marked as enduser visible? “In principle, this approach is applicable to any CAD file”, Shugrina told EETimes Europe, “but the customizable design parameters would have to be chosen at the start of the design process, by the designer”. By thinking “customization” early-on in the design process, designers and brands could somehow give an orientation to the design exploration space they put forward. Although it could certainly be possible to design a special tool to figure out which set of parameters should be made end-user visible, Shugrina does not envisage existing CAD part libraries to be automatically converted to offer the new customization service. Instead, the algorithms could be implemented as a standalone feature in CAD tools to perform fast design exploration and CAD modelling in the cloud. Regarding intellectual property rights, the issues are circumvented by preventing the user from downloading the actual modified CAD files, explained Shugrina. A modified design could be made available only for direct 3D printing. The 3D printing company would charge for its services, and the designer would get a royalty for every new print implementation from within the exploration space of his/her original design. 4 Electronic Engineering Times Europe October 2015 www.electronics-eetimes.com


EETE OCT 2015
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