Additive Manufacturing

JUL 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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JULY 2018 Additive Manufacturing 16 TAKING SHAPE Printing End-Use Parts from High-Performance Ceramics By Barbara Schulz automatically assure that one batch of powder is sufficiently similar to a batch that preceded it. This evaluation is perhaps most germane where recycled powder is used, Mulherin says. Today, strategies for reusing powder from build to build typically involve switch- ing to virgin material after an arbitrary number of cycles to ensure sufficient powder consistency. The SEM analysis can eliminate the need for this arbitrary cutoff, and thus eliminate the potential waste that comes from disposing of recycled powder too soon. Instead, the manufacturer can just keep on using the powder until inspection reveals that its composition or morphology has meaningfully changed. The same analysis applied to finished parts scans for microscopic shapes that are either light or dark against the 3D-printed sample. Inclusions could be lighter or darker than the surrounding material; voids are darker. "If a dark form within the part measures no X-ray response, then we know it's a void," she says. This measurement requires a flat, smooth surface. The part itself is therefore not inspected this way, but instead a test coupon is grown with the part, which is polished for the SEM measurement. The coupon can then be saved for traceability. Analyz- ing the material quality of an AM build is one application, but once the build has been analyzed and its acceptable variation has been established, the SEM unit offers potentially an even more valuable role. That is, control limits for the part number can be established in the form of acceptable values for the sizes of material defects. With these limits defined, the operator with no metallurgical expertise can scan a test coupon to confirm it falls within required specs. Indeed, control limits could be estab- lished to define acceptable powder as well, Mulherin says. In this way, for both the raw material going into to the additive process and the part coming out of it, the compact SEM analyzer can be applied in production as a simple but effective pass/fail gage. Components made of high-performance ceramics are mainly used under ther- mally, mechanically or chemically demanding conditions. Currently, such components are rarely produced using additive manufacturing. However, AM's significance will increase in the future due to many positive factors such as time and cost savings. Added to this is the extremely positive environmental balance, says Michael Steinbach, who heads the Technical Ceramics division of Steinbach AG, located in Detmold, Germany. Under the direction of Steinbach, the division underwent a dynamic expansion at the beginning of 2016 when the company pur- chased 3D printers and state-of-the-art furnaces, enabling them to introduce their product line "Form Ceram." To additively manufacture ceramic components, Steinbach uses the lithography- based ceramic manufacturing (LCM) process. The starting material for this process is a suspension consisting of ceramic powder and a UV-light-sensitive monomer, referred to as a "slurry." UV exposure causes the polymerization of the material and thus the solidification of the liquid suspension. Before printing, the CAD data is sliced into individual layers (layer thickness 25 micron). The build platform is then submerged into the slurry. UV exposure leads to polymerization turning the liquid slurry into a solid. This process is repeated until the desired height and contour of the component has been reached. "The parts are then cleaned and placed into a debinding furnace for up to six days," Steinbach says. In production, the SEM unit can be used as a pass/fail gage enabling any operator to quickly determine whether parts or powder meet specification

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