Use Formlabs Castable Resin to produce detailed fine jewelry through the investment casting process. Developed specifically with investment casting in mind, Castable burns out cleanly with no ash or residue.
Castable Resin is an acrylate photopolymer, which requires a different process from a traditional wax schedule. Instead of melting at low temperatures, Castable Resin transitions to a gas. The recommended burnout schedule is designed and tested to allow Castable Resin to transition into a gas gradually. The slow transition reduces the possibility of the investment cracking due to rapid expansion of the printed part. To fully enable the gas transition, maximize the airflow by adding venting, by active ventilation, or by blowing out molds when possible. Ideally, the thermal expansion of the investment should be well suited to the thermal expansion of your 3D printed material. To transition from primarily a wax-based casting process, adjust the process accordingly to achieve a successful cast.
Note:Some customers have reported success in casting Formlabs Clear Resin. More advanced casting houses familiar with successfully casting photopolymers may want to try this material, which offers high detail, good surface finish, and a faster cure cycle.
Read further to understand the step-by-step workflow, recommendations, and special considerations for designing, printing, preparing investments, and burning out Castable Resin. The instructions for each phase in the process include troubleshooting tips. This information is provided in a similar downloadable publication, Formlabs Application Guide: Recommended Burnout Process and Casting Guide.
Made by Formlabs
- Form 2 (SLA) 3D Printer
- Castable Resin
- PreForm Software
- Finish Kit or Form Wash
- Form Cure
Made by third parties
- R&R Plasticast with BANDUST investment* - Find a dealer
- Furnace, vacuum investment machine, and casting system, such as Indutherm MC-series
- Alternative curing solutions: NextDent LC Curing Lightbox or Gesswein UV Curing Chamber
For best results, print with Resin Tank LT (Long Term). Standard Resin Tanks may wear more quickly and may print less accurately with this material. Learn more about resin tank compatibility for Formlabs materials.
*Recommended Investment: Formlabs specifically recommends Plasticast with BANDUST. If seeking alternatives, look for investments advertised to work with photopolymers. Customers have reported success with Kerr SatinCast and Omega+ by Goldstar Powders. You can also experiment with bonded investments, like those typically used for dental applications. Some casting houses have also developed proprietary investments. When using alternative investments, refer to the manufacturer for instructions and burnout recommendations.
Design for Casting
Casting is both a skill and an art form. For successful results, the design of the piece to be cast is as important as the material properties. Learn more in our whitepaper, Jewelry 3D Printing: Basic Design Parameters, Supports, and Orientation.
Pay attention to the design of individual features, the flow of material in the investment, and the printing configuration. Consider the following factors when designing each part:
- Design for material flow when modeling. Avoid sharp corners and reduce transitions between thick and thin profiles on the same piece. Design for the negative space to easily fill with investment.
- Instead of adding wax sprues post-print, use CAD software to create and print sprues with the printed piece. For 3D printed sprues, design the sprue diameter to match the cross-sectional thickness of the adjacent wall or part.
- Design thicker models to be hollow in CAD (possible through a program like Meshmixer) and print a thin-walled shell. See Formlabs’ Design Specs for guidance. A hollow cavity allows the part to collapse inward instead of only expanding outward against the investment. For more elaborate or larger hollow pieces, consider designing internal struts.
- When preparing prints in PreForm, check for the proper orientation and support creation. For complex and highly detailed pieces, consider designing custom supports in your CAD program. Fine supports can be used on individual prongs or fanned out along the inside of a ring with detail all the way around its surface.
Print and Prepare Parts
Use PreForm software to configure each part to print with optimal orientation and support.
Agitate Castable Resin by shaking the cartridge and mixing resin in the resin tank before printing. Castable Resin contains a component, called titanium dioxide, that separates from the rest of the mixture when left unused. The separation appears as white crystalline or flake-like deposits, often on the outside of the resin tank or printed part. Mix the resin regularly to maintain or restore normal resin performance.
The Fine Detail settings are an option available in PreForm when using Castable Resin (FLCABL02) and printing on a Form 2. These settings were optimized for printing jewelry, with a focus on achieving the features and detail that matter to jewelers. For the majority of designs, printing with the 50 micron layer height provides the best results and superior print speeds. Learn more about the best design parameters for common jewelry features, such as prongs, filigree, engraving, surfaces, raised text, and milgrain, in our Designing for 3D Printed Jewelry whitepaper.
After printing, follow the standard post-print procedure and consider the suggestions below that are specific to washing and post-curing Castable Resin.
For extra care when washing Castable Resin prints, use two short sequential five-minute rinses in clean 90%+ isopropyl alcohol (IPA). Do not leave parts in IPA longer than necessary. Allow the parts to fully dry after removing them from the IPA bath. Make sure the IPA is fully evaporated prior to post-curing and casting as it could interfere with the investment and cause pitting.
To maximize part strength and increase the parts’ integrity in the investment, prints made with Castable Resin should be fully and evenly post-cured on all surfaces. Post-cure the parts under 405 nm light and heat until the surface is hard and rigid.
Post-curing solutions vary widely in terms of heating capability, light wavelength, and output. When using Form Cure, post-cure Castable Resin parts at 60 °C for at least four hours. Small UV sources like home UV nail dryers use UV light (0-400 nm) and may take up to eight hours to properly post-cure parts, while industrial UV curing ovens may take only two hours.
Rotate parts during post-curing to ensure even exposure to the light and heat. Form Cure will automatically rotate parts, but if using another method, it may be necessary to manually flip or rotate parts during the post-cure.
Note:UV nail salons prove an effective entry-level solution, partly because the parts are typically placed very close to the bulbs. The parts get very hot (sometimes greater than 60 °C) and the heat helps the parts fully cure. Higher cure temperatures provide a faster cure, but make sure to inspect parts for warping.
During post-curing, part color might change from bright blue to dark, matte blue. This photobleaching is a natural effect of some types of light. If a portion of the part is photobleached, this is one indicator of sufficient light exposure. When post-curing the part with supports still attached, add 30 minutes of additional post-cure time after removing supports to fully post-cure the touchpoint surfaces.
It is important for all surfaces under the supports to be cured evenly. For larger parts like bracelets, it can be beneficial to cure on supports to counteract any possible warping and help the part retain its original shape at higher temperatures.
Tips for Printing and Preparing Castable Resin
- Instead of one long soak, wash parts multiple times for short periods in very clean and highly concentrated IPA. Do not leave parts in IPA longer than necessary.
- Ensure printed parts are fully dry and all IPA has evaporated prior to post-curing.
- Post-cure parts for at least 4 hours at 60°C in Form Cure. Extend the post-cure time until parts feel adequately rigid, particularly for larger and thicker pieces. 80 °C may be used for a faster cure, but be wary of possible warping on fine or delicate parts.
- After removing supports, perform an additional cure cycle if there are still soft, bright blue, uncured spots on the surface. Curing parts longer is always preferable to having semi-cured parts. Extend your post-cure time as your process allows.
Finishing and Sprueing
Polish the surface using polishing paper or a rotary tool with a buffing attachment. Do not finish the print with mineral oil after sanding.
Add wax sprues and gates to the print, similar to lost-wax casting. Ideal positioning varies with part geometry. Place thicker parts at the bottom and thinner parts at the top of the tree. Space 3D printed pieces further apart on the tree than typical for a tree of wax pieces. More investment in the gaps between parts helps resist any thermal expansion.
Tips for Creating a Casting Tree:
- If using wax sprues, create the thickest sprues possible and place them on the thickest part of the model (if it doesn’t interfere with the design).
- For printed sprues, match the sprue diameter to the cross-section of the adjacent part for even expansion.
- Whether wax or printed, place sprues for the shortest exit path of material. Make the path of airflow inside the cast as short as possible. Smaller trees with less resin burn out more easily.
- If possible, thicker parts should be hollowed out (see Design for Casting). Add ventilation holes within the design to ensure sufficient airflow during burnout. Close these holes with wax before adding sprues to avoid the investment getting inside the model.
Prepare the Mold
Plasticast with BANDUST has proven to work best with Formlabs’ Castable Resin. Plasticast is also compatible with mixed trees that include wax and resin parts and can be used within the same burnout cycle.
The workflow for mixing the investment and preparing the mold varies depending on flask size. Follow the investment manufacturer’s instructions and adjust the burnout schedule as needed.
5. Carefully remove rubber sprue base from the flask and allow it to set in a vibration-free environment for 2-6 hours.
WARNING:Follow the investment manufacturer's safety recommendations.
Place the casting flask in a cold furnace and heat. Use the Formlabs burnout schedule (download a PDF or continue reading) for guidance. Adjust the burnout schedule depending on the investment instructions, flask size, and final casting material. When starting the burnout with a preheated oven, rest the flasks for at least 5 hours. Otherwise, the plaster might crack when the water expands and turns into steam.
To provide sufficient airflow throughout the chamber for the resin vapor to be carried out the exhaust, use a well-ventilated furnace with ventilation at the top and at the bottom of the oven. Venting is essential, but airflow may reduce the temperature in the oven. As much as possible, monitor the oven and flask temperature. Adjust the process as you develop a burnout schedule suited to your own equipment.
- If there is suction on top of the oven, set for the maximum suction to create higher airflow throughout the oven.
- If the oven is full of flasks, the airflow is less effective per flask. Attach an oxygen generator to the oven to increase the airflow.
- Maximize the airflow and ventilation during burnout. Adjust the burnout schedule for temperature fluctuations as a result of increasing airflow.
The burnout schedule consists of four phases. Various factors, such as part thickness, total resin volume, flask size, investment type, and final casting temperature affect the ideal burnout schedule. Use this burnout schedule as a starting point and make adjustments as needed.
Click the thumbnails to view the full-size images.
|Insert flasks into a cold oven||Insert Flasks||0 min||20 °C (room temp)||68 °F (room temp)|
|Castable Resin starts to burn out, transitioning directly from a solid to a gas.||Ramp||150 min||for 150 min (~1 °C per min)||for 150 min (~1.9 °F per min)|
|The slow ramp rate and added hold allow the transition to happen slowly, reducing the chance of cracking in the investment.||Hold||30 mins||177 °C||350 °F|
|Castable Resin continues to burn out. The duration of this ramp should be adjusted depending on the size and number of flasks, and the thickness and total volume of Castable material being burned out.||Ramp||270 min||for 270 min (~2.1 °C per min)||for 270 min (~3.7 °F per min)|
|Castable Resin should completely burn out during this hold. The duration of this hold depends on the size and number of flasks, and the thickness and total volume of Castable material being burned out. Thicker parts require a longer hold. Increased airflow inside the oven may allow for a shorter hold.||Hold||180 min||732 °C||1350 °F|
|The last ramp takes the flask down to your desired casting temperature.||Ramp||150 min||for 150 min (~-1.7 °C per min)||for 150 min (~-1.8 °F per min)|
|The hold allows the center of the flask to reach this lower temperature. Adjust this hold relative to the size and number of flasks.||Hold||60 min||482 °C (or desired casting temperature) for 60 mins||900 °F (or desired casting temperature) for 60 mins|
|Remove flasks at your desired casting temperature||Remove Flasks||482 °C||900 °F|
Finishing After Casting
Remove the mold from the furnace and cast metal. Centrifugal or vacuum casting processes can be helpful in quickly filling the mold.
Tips for Mastering the Burnout Process
- Use Formlabs recommended burnout schedule as the starting point. Adjust the burnout schedule according to investment manufacturer instructions. Adjust the ramp rate and hold times dependent on part geometry, total volume, and flask size. Adjust final hold temperature dependent on metal casting temperature.
- Calibrate your oven regularly to allow for the most accurate display of cycle times and temperatures.
- Compare the casted part to a printed model after casting. If pieces appear to be missing from the casted part, there is likely ash remaining in the investment cavity before casting. In this case, review the post-curing or burnout steps.
Success with Castable Resin depends on more variables than other Formlabs materials due to the additional steps in the casting workflow. Consider the tips and recommendations at each step of the process when evaluating or troubleshooting issues. The troubleshooting tips included here are also compiled and available for download: Castable Resin Troubleshooting Checklist.
To learn more about casting and 3D printing, Formlabs compiles additional knowledge about 3D printing, jewelry design, and casting in our Jewelry Resources webpages.
Formlabs specifically recommends Plasticast with BANDUST. When using alternative investments, refer to the manufacturer for instructions and burnout recommendations.
Special thanks to Lars Sögaard Nielsen and the KEA (Copenhagen School of Design and Technology) for letting Formlabs document their casting process.