Additive Manufacturing—Medical
Building a Stronger Frame However, it was clear that Emma would need a stronger WREX as she grew and used the frame in the ways typical of a growing child. Rahman and Sample turned to Noah Zehringer, a senior ap-
plication engineer at Stratasys, for support. “I worked with them to refine the way they were printing the components,” Zehringer said. “The way you print them can make them stronger.”
More Information White Paper:
Precision Additive Manufacturing of Medical Device
http://tinyurl.com/rapidmedical
Several materials and printing orientations were tested for strength using load tests. In all, four different sets of compo- nents were tested until failure. The first set of parts was built in a flat orientation. The second set was built with default parameters in an alternative orientation to better handle the
forces acting on the component. The third set was built us- ing parameters optimized by Stratasys’ Insight software. The fourth set was built in the same manner as the third set but with a new material, ULTEM 9085.
“One of the critical factors is the orientation and so just by changing the orientation of the part, you can get different properties,” Zehringer said. “It’s all geometry-dependent.” One way to think of strengthening a part through build orientation is to think of building a pen horizontally (X axis) or vertically (Y axis). An object built with additive methods is weakest where the layers are joined together. So a pen would be easier to, say, snap in half if it is built vertically rather than horizontally or in some other alternative axis. In the component tests, Zehringer said, “Simply changing the orientation yielded a 48% increase in strength.” Using Insight software to optimize the toolpaths yielded a strength increase of another 47%, for a total 117% increase in strength from the original part. Changing ABS to ULTEM 9085 yielded a strength increase of 124%, or a total of 387% over the original part. ULTEM 9085 has a high strength-to-weight ratio and has an FST (flame, smoke, and toxicity) rating. The material’s preexisting certifications make it an excellent choice for the commercial transportation industry—especially aerospace, marine and ground vehicles. The only Stratasys systems that build with ULTEM 9085 are the Fortus 400mc and 900mc. The ULTEM 9085, a material that is manufactured by SABIC Innovative Plastics (Pittsfield, MA), was almost as light as the ABS, too, with a specific gravity of 1.34 compared to 1.04 for the ABS. “It’s very similar in weight,” Zehringer said. “It’s slightly heavier, but much stronger for its weight.” Ultimately, Emma, now about five years old, ended up with a strong, light WREX to help her navigate the world like a normal child. Today, nearly 50 children use custom 3D-printed WREX
devices. Like Detroit,
we’ve been automating your world for over 50 years.
When Emma grows out of a part or breaks a piece of her WREX, Sample said, “I don’t have to worry about lead time to machine something.”
In fact, Nemours just purchased a Stratasys Fortus 400mc. Sample uses the Dimension for his prototypes and the Fortus for actual parts. “I’m going to be using them both out the wazoo,” Sample said. Once only able to do three–four WREX devices a year made out of aluminum and steel, he now does about one
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ManufacturingEngineeringMedia.com | April 2013
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