Optimizing Strength on Emma’s “Magic Arms”
Stratasys posted on October 30, 2012 | | 3349 views

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Fused Deposition Modeling (FDM) produces some of the strongest parts in the industry, but even FDM parts can be improved with a little know-how. Stratasys application engineer Noah Zehringer got the chance to help medical researchers improve Emma's "magic arms," which is what a four-year-old child calls her 3D-printed assistive exoskeleton.

Here’s Noah’s report:

We did some work with one of the designers at Nemours/Alfred I. duPont Hospital for Children to improve the strength of one particular component of Emma's orthotic device. The results were both interesting and fairly consistent with what we expected.

We set up a test fixture to mimic the loads that would be applied to the component in real-life scenarios. We attached a 7-inch arm to the FDM component we were testing, then added weight until the component failed. We tested four different sets of components, and the results were consistent for each set.

The first set of parts was built with default parameters in a flat orientation. The second set of parts was built with default parameters in an alternative orientation to better handle the forces acting on the component. The third set of parts was built in the improved orientation with the build parameters optimized using Insight software. And the fourth set of parts was built in the same manner as the third but in an alternative, stronger material — ULTEM 9085.

The results: Simply changing the orientation yielded a 48 percent increase in strength. Using Insight software to optimize the toolpaths yielded a strength increase of another 47 percent (a 117 percent increase in strength from the original part). And changing from ABS to ULTEM 9085 material yielded an additional strength increase of 124 percent (a 387 percent strength increase over the original part!).

In addition to the already robust thermoplastic materials, optimizing the part orientation and using Insight software to adjust the toolpaths can provide even stronger results. This becomes increasingly important as more people embrace rapid manufacturing and start using FDM as an alternative to plastic injection molding and other traditional processes.

If you haven't seen the video of Magic Arms in action, check it out.

You can also read the full case study here.