By Christina Krueger
Keeping on trend, Root3 Labs created a long list of quarantine hobbies, which included finally testing out Formlabs’ Elastic Resin (50A) with our in-house Form 2 Stereolithography (SLA) 3D printer. In January 2019, Formlabs released the Elastic Resin and compared it to a Shore 50A durometer silicone. The family of Flexible and Elastic Resins began back in 2014 with the original Flexible Resin (80A). This resin has since been discontinued and replaced with newer versions that compare to a rubber or TPU. The newest Flexible Resin (80A) was released in June 2020, in the midst of a global pandemic, piquing our interest in the Flexible and Elastic Resin family.1
In the world of rapid prototyping, complex silicone prototypes can be time consuming and expensive to produce. At Root3 Labs, we typically complete a multi-step process involving designing the mold, 3D printing the mold parts via high-resolution stereolithography (SLA), and then casting the prototypes in the 3D printed mold using a two-part liquid silicone rubber (LSR). This is a timely process to iterate for only a few molds in most cases. Leveraging 3D printing allows us to iterate through design revisions without the large upfront costs of an injection mold. However, a part cast using a two-part LSR will not achieve the same material properties as a part injection molded using LSR. This can make testing difficult if the design relies on stressing silicone’s more favorable material properties such as its drastic elongation before break. The ability to 3D print the silicone part directly using Formlabs’ Elastic Resin (50A) would drastically reduce the time and cost of rapid design iterations. The functionality of these prototypes depends on the performance of the cured Elastic material under the application’s stresses. According to the datasheet provided by Formlabs, the Elastic resin has 160% elongation at failure if it is post-cured2. A comparable two-part platinum cure silicone from Smooth-On has a 320% elongation at break3, and a comparable injection molded LSR from Wacker has a 490% elongation at break4. In our experience, the 3D printed, post-cured Elastic material has drastically reduced performance compared to other production methods. However, it still proves useful for “feels-like, looks-like” parts or designs that can account for the lower percent elongation and ultimate tensile strength.
Based on our testing using the Form 2 SLA 3D printer, the Elastic Resin is finicky. It is sensitive to cupping during the build process, needs more supports than the rigid resins, and requires post-processing to achieve adequate material properties for most applications. We achieved several successful prints with relatively complicated geometries. Supports are a huge consideration for the Elastic Resin. Since the supports are also flexible, supports over 20mm long can lead to print failures2. The models need supports with a higher density and larger touchpoint than when printing in the rigid resins. Our successful prints used a density of 1.00 and touchpoint size of 0.5 mm. A smaller touchpoint size makes the supports easier to remove and leaves a smaller residual mark. The higher support density is necessary for the Elastic Resin, but it makes the surface finish less desirable. The Elastic Resin is not easily smoothed with sanding or bead blasting like the rigid resins. The Elastic Resin also has a hard time joining two separate features together during a print. Formlabs recommends printing any branching features, such as a “Y” shape, with the single branch closer to the build plate1. In this orientation, the printer will branch from a single point as opposed to printing two separate branches that have to join later in the print. Sometimes joining two branches is unavoidable in a design. In our experience, the two branches will merge with flaws since the flexibility of the resin challenges tolerances. Any imperfections quickly propagate into total destruction as the part tears itself into pieces. A “green” part fresh off the printer will quickly tear if bent or stretched. However, a part that is post-cured will hold up to a good amount of manipulation.
Overall, although the Elastic resin fails to compare to cast or injection molded silicone’s, the Elastic resin is an exciting dive into a new world of possibilities with 3D printing.
- (n.d.-a). Resin version history. https://support.formlabs.com/s/article/Resin-version-history?language=en_US#elastic
- (n.d.). Using Elastic 50A Resin. https://support.formlabs.com/s/article/Using-Elastic-Resin?language=en_US#:%7E:text=The%20surface%20of%20Elastic%2050A,removing%20supports%20to%20avoid%20breakage.
- Smooth-On, Inc. (n.d.). Smooth-SilTM950 Product Information. https://www.smooth-on.com/products/smooth-sil-950/
- (2020, January 7). Elastosil LR 3003/50 A/B. https://www.wacker.com/h/en-us/silicone-rubber/liquid-silicone-rubber-lsr/elastosil-lr-300350-ab/p/000005258