Research Overview:
Achieving discoloration due to the overcuring process in stereolithographic (SLA) 3D printing requires a resin that is susceptible to color change during material degradation, so research was conducted to find the correct resins to test the overcuring process. As the Formlabs Form 2 and 3 were the only SLA printers immediately available for use for this project, the resins that could be tested were limited to Formlabs resins. From background research into overcuring, non-transparent resins weren’t found to have any color change during degradation, so the material property sheets of Formlabs transparent resins were examined. The material property sheet for Clear Resin, which was used in this print experiment, is shown in Figure 1.
Figure 1: Formlabs material property sheet for Formlabs Clear resin (1).
When examining the material properties of each transparent material, there was not a measure of a material’s degradation when subject to UV light. It was assumed that the heat deflection temperature would be the most similar property, but the formlabs blogs were investigated to obtain additional information before this assumption was acted upon. While browsing the formlabs blogs, a discussion on overcuring formlabs resin to change the color of the resin was found. In this discussion, formlabs employees did not think it would be possible to change the color of the resin with their printers, and it would simply make the overcured areas more brittle and easy to break. Further in the discussion, it was found that polycarbonate-like resins such as Accura and Somos Watershed had been successful in creating different colors when overcured. With this in mind, Formlabs Clear resin was chosen for our first print as it is similar to the Accura and Somos resins.
Printing Technique/Manipulating Printing Software
For the initial proof of concept, the intention was to overlay several parts into one. In doing so, the team hoped to reproduce the discoloration within the region that is overcured. Figure 2 shows the setup within Formlabs’ software, PreForm 3D. Unfortunately, the software automatically signaled an error when parts were overlaid on top of each other. In addition, the generation of supports was difficult since the software wanted to generate individual support structures for each part, resulting in a significant amount of support resin that is difficult to remove. A single support structure for the resulting overlain part would have been more desirable since it would waste less material and make post-processing easier.
Figure 2: Layout of print in FormLab’s software, PreForm.
As a result of the difficulties encountered with PreForm 3D, progress was slower than expected. However, Figure 3 shows the result of a successful print. It can be observed how each of the cubes is overlaid on top of another within the fishing lure. It was expected the cubes would undergo discoloration as a result of the SLA printer’s UV rays curing them more frequently than normal. Additionally, it was expected the region where there is overlap between the cubes and fishing lure would experience greater discoloration. In Figure 2, the region of interest is slightly less transparent and more discolored than the rest of the fishing lure, but not to the extent that was theorized. It is expected that as the number of curing passes increases, prints will become darker in the regions of interest. This will be further tested in the future.
Figure 3: Comparison of failed print (top) and successful overlain print (bottom).
Future plans
This coming week we will be working with the Fab Lab at the Morgridge Institute for Research to print another test prototype using a slightly different setup. Their lab has a Viper SLA printer that uses Accura 60 resin that is more prone to UV light degradation and therefore overcuring. Using this setup will ideally yield more noticeable results with less UV exposure and will give us a better idea of how much UV exposure is needed to print a workable prototype. Our initial plan is to print a small rectangle with multiple smaller cubes or rectangles inside that are “printed” varying amounts of time to increase levels of UV exposure and determine how much UV exposure is needed to print a workable prototype. A model of this print is shown in Figure 4. We would like to pinpoint how much UV exposure is needed on the small rectangular piece before we try to print our prototype in their lab due to the expensive nature of resins.
Figure 4: Proposed print layout for varying degree of degradation.
Once we complete this test print at Morgridge, we want to try a similar test print at the Makerspace to compare the resins at use. If all testing goes well, we would like to try a print of a fishing lure that has the spine and structure overcured on the inside to give the illusion of a translucent fish.