Jewelry Burnout Photopolymers for Casting Jewelry Through 3D-Printed Models
Jewelry burnout photopolymers have entered the technological cycle of jewelry production relatively recently. However, one undeniable advantage of creating 3D-printed jewelry models is the speed of reproduction and copying, which does not affect their intricate precision and detail. The use of laser 3D printing on Formlabs 3D printers and specially developed 100% burnout resins, such as Castable Wax Resin, Castable Wax 40, and Castable Resin enhances the jewelry manufacturing process.
When casting using burnout models, a hollow mold is created from a master template, either handcrafted or 3D-printed, using jewelry burnout photopolymers.
The master template is immersed in a refractory casting material (or "investment material") that dries and hardens. The wax or 3D-printed model burns out, leaving a negative impression of the design in the plaster. Metal is then poured into this cavity, and after solidification, the final piece is obtained.
Wax patterns for intricate jewelry are difficult to craft by hand, and in a world of high demand and fast fashion, handmade items can struggle to keep up. Modern materials and accessible 3D printers, such as Form 3, are transforming the methods of jewelry manufacturers and designers, bringing industrial-quality precision to the workspace and simplifying the production and fitting of complex geometries that once required hours of meticulous labor.
1. Design for Casting
Use CAD software like RhinoGold, JewelCAD, or 3Design to transform your models from concept to 3D-printed prototype using these advanced methods.
The design of traditional wax models and 3D-printed resin models takes many principles into account, such as the importance of smooth material flow. Avoid sharp angles that can increase turbulence. As with wax, orient the design to fill large voids and smaller channels and details.
Sprues
While large feeding sprues can be made from conventional wax, small sprue channels can be 3D-printed to save labor and improve mold filling for fine details. Feed sprues should be straight or taper toward the piece.
Supports added in PreForm should not be used as sprues. If printing sprues on a 3D printer, we recommend incorporating them in your CAD design.
Filigree
The exceptional detail of Castable Wax Resin allows for creating pieces with intricate filigree. These delicate wire meshes look complex but can be cast with carefully designed sprue placement.
For printing fine meshes, wire diameters as small as 0.3 mm can be used. Printed filigree is fragile and easily damaged when removing supports. Design filigree components to be as self-supporting as possible. 3D-printed sprues can serve a dual purpose, acting as supports that are removed after casting.
To prevent metal from freezing in these thin channels, add sprues that feed metal to multiple points around the filigree mesh.
Large Parts
Formlabs Castable Wax Resin is suitable for printing and casting large jewelry and other cast parts. Convert your design into a thin-walled shell to minimize the expansion forces of the investment during burnout. For parts thicker than 4 mm, add drainage holes so that resin can be washed out of the internal cavity. Uncured resin will not burn cleanly, causing ash defects.
Formlabs recommends using 0.7 mm walls for hollow shells printed with Castable Wax Resin. A lattice structure can also be added inside to increase strength when working with large components.
2. Printing and Preparing the Part for Casting
Jewelry blanks can be printed in large batches on a desktop Form 3 3D printer. Arranging parts on the build platform ensures maximum efficiency and 3D printing productivity. After printing in the desired orientation, follow these steps to prepare blanks for sprues and investment.
Washing
This involves carefully rinsing the parts in a 90% isopropyl alcohol (IPA) solution. It is crucial for obtaining a clean casting. Excess uncured resin can hinder burnout casting and cause defects such as pinholing.
Allow parts to dry completely after removing them from the IPA bath. Use compressed air to evaporate all IPA before post-curing and investment. If Castable Wax parts remain sticky after washing and drying, IPA may need to be replaced.
Note: Do not leave parts in IPA longer than necessary. The Form Wash automatically lifts parts from the IPA to avoid accidental over-washing and deformation.
Drying
The polymer structure of the resin part must be fully cured using 405 nm wavelength light to facilitate complete burnout. Formlabs resins cure differently on the Form 3 printer, and some require post-curing if they are to be cast as burnout models.
Castable Wax Resin does not require additional post-curing and provides enhanced casting efficiency. Post-cured Castable Wax parts may shrink slightly (<1%).
Expose Castable Resin parts until the surface becomes hard and rigid. Rotating parts in a curing unit ensures even curing. The Form Cure rotates parts automatically, but manual rotation may be required if using other post-curing methods. Castable Resin changes color from bright blue to dark matte blue during post-curing.
3. Building the “Sprue Tree”
Attach post-processed prints to the main wax sprue using sticky wax. Melt the wax to create smooth joins between each printed pattern and its feed sprue.
Place thicker parts at the bottom and thinner parts at the top of the tree. 3D-printed parts may require slightly more space between components than traditional wax trees. When casting large thin-walled parts, ensure all drainage holes are filled with wax to prevent investment intrusion.
Surface-Active Coating
A common casting defect is caused by bubbles trapped around the model during mold pouring. Low-cost surfactants or "debubblizers," such as Wax Wash, help prevent bubbles from sticking to the prints. Surface-active coatings are especially useful for filigree models prone to bubble entrapment.
Formlabs recommends immersing the tree with models in a debubblizer solution and allowing it to dry completely before pouring investment.
4. Preparing the Mold
The following steps are standard for preparing any investment flask.
A vacuum investment machine helps mix, degas, and pour the investment cleanly and evenly. Alternatively, a separate mixer and vacuum chamber can be used.
1. Attach the flask to the base of the sprue. If the flask has perforations, wrap with clear packing tape to prevent investment leakage.
2. Mix the investment powder and cold distilled water according to the manufacturer's instructions. Slightly less water generally increases the strength of the investment, though viscosity will also increase (making degassing harder). Mix at low speed until fully wetted.
3. Slowly pour the investment along the flask wall, avoiding the model tree. Smooth pouring prevents trapped bubbles. Use a vacuum chamber to remove bubbles from the flask. Allow the investment to set and dry.
4. Carefully remove the rubber base of the sprue from the flask and allow it to harden in a vibration-free environment for 2–6 hours. Follow the manufacturer's safety recommendations. Use a respirator.
5. Burnout and Casting
Place the flask in a burnout furnace and heat according to the recommended burnout schedule. Adjust according to the size of the flask, amount of printed material, and investment instructions.
If starting burnout in a hot furnace, ensure flasks rest at least 5 hours to prevent cracking from water expansion and steam.
Formlabs recommends using a well-ventilated furnace to ensure adequate airflow and safely remove all vaporized polymer material.
Short Burnout
Castable Wax Resin is 20% wax-filled, allowing printed models to partially break down earlier in the burnout cycle, resulting in faster burnout times.
Short burnout is limited by geometry and higher-cost investments like Ultravest Maxx from R & R. See the Castable Wax User Guide for details.
Notes:
• Ventilation is necessary but may lower furnace temperature. Monitor temperature and adjust your burnout schedule accordingly.
• Maximize airflow when using active ventilation to improve circulation.
• Fully loaded furnaces burn less effectively. Consider using an oxygen generator to increase airflow.
Casting
Remove the mold from the furnace and pour the metal. Centrifugal or vacuum casting machines, such as Neutec J2R (USA) and Indutherm MC series (EU), are easy to use and well-controlled. After casting, cool the mold thoroughly in water and remove investment.
Compatibility with Precious Metals
Formlabs has tested gold, silver, and bronze castings from Castable Wax models. Metal compatibility primarily depends on the investment. Different metals require varying heat resistance from the investment. Complete burnout of Castable Wax requires a minimum temperature of 732 °C. Consult the manufacturer if unsure about resin pattern compatibility with a specific investment.
Burnout Schedule for Photopolymers
Formlabs offers Castable Wax and Castable Resin for jewelry burnout casting. Castable Wax Resin provides flexible burnout schedules. With Castable Wax, follow the manufacturer’s instructions for investment. Castable Resin, a previous-generation product, requires a more precise, gentle burnout schedule.
Below are recommended schedules for each material with R&R Plasticast using BANDUST investment.
Jewelry Burnout Photopolymers: Castable Wax Resin, Technical Properties:
Jewelry Burnout Photopolymers: Castable Resin, Technical Properties:
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