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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Page 27 of 43

MAY 2018 Additive Manufacturing FEATURE / AM for Tooling 26 windows for the Domino Sugar Refinery development. This Brooklyn, New York, development will feature several new build- ings and recreational space surrounding the historic Domino Sugar Refinery. One of these new constructions is a 42-story complex that includes office and retail space as well as apart- ments. Gate Precast is making 993 precast concrete panels for the residential portion at the facility in Winchester, Kentucky. (Its Oxford, North Carolina, plant is making an additional 612 panels for the commercial and retail parts of the building.) Gate Precast won the Domino Sugar Refinery job with a quote based on the cost of making the forms in wood, but knew that this would be a major undertaking. Just to build the wooden forms would have taken 9 months, says Steve Schweitzer, vice president of operations. It wasn't a given that Gate Precast would be able to build all these forms itself, and farming the work out to subcontractors would likely drive the price up. But with the success of the cornice forms in testing in Tennessee, 3D printing began to look like a viable option. 3D-printed forms may not be worthwhile for a lot of pre- cast concrete jobs. Architectural precast work, like what the Winchester plant performs, can be small batches and one- offs for which a wooden form can be built quickly and cheaply. But the Dom- ino Sugar Refinery project is a job on a completely different scale, illustrating the transformative possibilities of 3D print- ing for concrete applications. Casting the hundreds of punched windows needed would demand durability and repeatability from the tooling—two things difficult to achieve with forms made of wood. Gate Precast approached ORNL and Two Trees, the contractor and owner of the Domino Sugar development, to discuss using 3D-printed tooling for the precast windows. Doing so also meant proposing a design change: reducing the number of different window profiles used on the building to make it cost- effective and practical to 3D print the forms. Fortunately, the owner liked the idea of using an unusual technology in the project and approved the change. ORNL began manufacturing the 40 3D-printed forms in five different window profiles at its facility in Knoxville, Tennessee, and eventually Additive Engi- neering Solutions (AES), a commercial BAAM user in Akron, Ohio, was brought on to help. About half of the forms are being manufactured in each location. The process starts with developing two CAD models for each mold: an "as-printed" version and an "as-machined" version, says Austin Schmidt, AES After casting and curing, each precast window undergoes a fin- ishing process. The surfaces are acid washed to remove the top film of concrete, and then certain faces are polished by hand, shown here, to expose the aggregate and create a sparkling effect. It takes 8 to 11 hours to 3D print each concrete form in the Big Area Additive Manufacturing (BAAM) system. Forms are then finish machined using a five-axis CNC router. Image courtesy AES.

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