Additive Manufacturing

SEP 2018

ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.

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SEPTEMBER 2018 Additive Manufacturing 12 TAKING SHAPE Large-Scale 3D Printing Supports Innovation in Construction By Stephanie Hendrixson Branch Technology's Cellular Fabrication (C-Fab) 3D printing process builds freeform, open geometries without the need for support structures. Material is applied within a 8 by 12 by 35-foot build envelope by a Kuka robot arm mounted on a horizontal rail. "In the architecture industry, buildings have been built out of the same post-and-lintel system for thousands of years," says Melody Rees, designer and product manager at Branch Technology. "But if you consider 3D printing as a method for construction, all of a sudden we have new methods to create buildings that liberate form and allow freedom to designers." This freedom is the goal for Branch Technology, a Chattanooga, Tennessee-based startup specializing in large-scale 3D printing for the construction industry. Through a process called Cellular Fabrication (C-Fab), the company 3D prints open matrices from high-performance polymers that can serve as architectural or structural pieces on their own, or as a framework for conventional building materials. Structures are typically 3D-printed in modular panels that can then be fitted together on-site. This approach to construction promises less waste, reduced labor and more innovative design possibilities. "Now without additional cost you can have new shapes and new forms, ultimately creating better buildings," Rees says. In the short term, this means structures with unusual geometries that can be prefabricated in a shop setting, using as little material as possible. But over the long term, Branch Technology sees 3D printing as a vehicle for more efficient construction and more sustain- able building practices. The C-Fab 3D printing process is driven by a Kuka robot arm mounted on a hori- zontal track, enabling it to reach the entire 8 by 12 by 35-foot build envelope and print from various angles. Branch Technology's proprietary printhead enables the material to solidify in midair as it is extruded, eliminating the need for support structures and en- abling scaffold-free features such as cantilevered or overhanging elements not typically possible with extrusion. But 3D printing is only as good as the material it uses, which is why Branch Technology has worked with materials design company Techmer PM for the past three years to develop and identify polymers capable of (1) supporting the large-scale projects it executes and (2) suited to its unique 3D printing process. In a recent example, Branch Technology built the "One City" band shell for the city of Nashville, Tennessee, a three-legged structure with an unsupported span of 42 feet (pictured on the facing page). The structure is composed of 36 3D-printed parts with the largest measuring 18 feet long. Getting to this design involved an extensive structural engineering process, as the initial shape for the band shell wasn't optimized for 3D print- ing. As designed, the printed structure would have needed hundreds of thousands of dollars in structural steel reinforcements in order to be safe. Branch Technology iterated the band shell to find a design as near as possible to optimal—one that would use the least amount of material while still meeting the strength requirements. Techmer PM's Electrafil carbon-fiber-reinforced ABS was used for its light weight, high strength and stiffness. (A 16-by-8-by-8-inch Electrafil matrix built with C-Fab can support more than 3,000 pounds.) "Through that process we were able to get to the best material use, to eliminate all the steel, and to use 3D printing to accomplish all the needs of the structure," Rees

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