Additive Manufacturing

MAY 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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AM / Precast Concrete, Meet 3D Printing 25 Enter 3D Printing Gate Precast manufactures precast con- crete in nine locations nationwide. Some of these facilities focus on structural concrete—weight-bearing items like the beams and columns that make up parking garages—which is produced with metal forms, often in very large quantities. Oth- ers, like its Winchester, Kentucky, plant, specialize in architectural pieces which are typically made in smaller batches. For most jobs, the Winchester plant builds its own forms in-house from plywood and fiberglass. These forms are not highly durable, but they don't need to be. A wood form will start to break down after 15 to 20 castings. But for a typical job where only 5 to 10 castings might be needed, this is no problem. It's larger jobs that are the challenge, when multiple forms must be built to support many concrete pours—which is where 3D printing comes in. Oak Ridge National Laboratory (ORNL) brought the idea to use 3D printing for concrete tooling to the Precast/PrestressedConcrete Institute (PCI), the industry's technical institute and trade association, as the result of a research collaboration. No printing was involved in that project, which focused on developing a lighter, thinner precast insulated panel. But ORNL is famously a co-developer and user of Big Area Additive Manufacturing (BAAM), the 3D printing system now sold commercially by Cincinnati Inc. that uses fiber-reinforced polymer to rapidly build large structures such as automotive parts and lay-up molds for composites. ORNL hypothesized that 3D-printed forms might help concrete precasters keep up with demand for concrete forms as master carpenters and form builders retreat from the labor force, while also shortening lead times, offering improved durability and potentially reducing costs. To test these ideas, the lab began 3D printing some test forms in a cornice shape. The forms were then sent to Gate Precast's Ashland City, Tennessee, plant, where between 30 and 40 cornice segments were successfully cast with no deterioriation in the tooling. The Right Job Comes Along This testing was taking place around the same time that Gate Precast had won a major new job: the production of punched The windows are poured in sets of three, with plywood serving as the outer wall of the form. Each pour happens in stages, allowing for the vibration of the platform to settle the concrete around the rebar and remove air as the pour progresses. It takes about three buckets of concrete to complete one window set. The 3D-printed forms are heavier and more costly than wood, but last for much longer— up to 200 concrete pours, versus just 15 to 20 for a wooden form. Image courtesy AES.

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