Direct investment casting, or lost wax casting, is a popular moldmaking technique that can be used to fabricate small and large parts in a wide variety of metals. Originating over 5,000 years ago, casting enables creators to work with a wide variety of materials and is one of the easiest ways to make metal parts.

In investment casting, a hollow mold is created from a hand-sculpted or 3D printed master pattern. The master is immersed in a refractory casting material (or “investment”), which dries and hardens. The wax or 3D printed pattern is burned out, leaving a negative mold of the design. Metal is poured into this hollow cavity to create the final part.

Wax patterns for intricate jewelry are complicated to produce by hand, and in a world driven by high demand and fast fashion, it can be difficult for hand-crafted pieces to keep pace. Advanced materials and affordable in-house 3D printers such as those from Formlabs are changing the way jewelry manufacturers and designers work, bringing industrial quality to the desktop and making it easier to produce and fit complicated geometries that once required hours of meticulous labor.

For more information on using True Cast Resin, read our support article here. 

Use CAD software such as RhinoGold, JewelCAD, or 3Design to take your parts from concept to 3D printed pattern using these best practices.

Products referenced:

True Cast Resin: A wax-filled material designed for precision casting of intricate jewelry to complex engineering components up to 5 mm thick. It delivers highly accurate parts with exceptional detail and smooth surfaces.

Castable Wax 40 Resin: A high wax-content direct casting resin with superior castability, accommodates a wide range of design features such as stone holes and engraves.

Castable Wax Resin: A lower wax-content, high green strength resin appropriate for ultra-fine structures such as wire filigree.

Delicate sprue channels can be 3D printed to save labor and improve mold fill to areas of fine detail. Design feed sprues that are either straight, or taper down towards the piece.

Supports added in PreForm should not be used as sprues. If you intend to 3D print sprues, we recommend incorporating them into your CAD design.

The exceptional detail of Castable Wax Resin allows you to create pieces with intricate filigree. These fine meshes of wires are challenging but possible to cast with careful sprue design.

Fine meshes can be printed with a wire diameter as thin as 0.3 mm. Printed filigree is fragile and easily damaged by support removal. Design filigree parts to be as self- supporting as possible.

In filigree designs, 3D printed sprues may serve a dual purpose as “supports” that are removed after casting. To avoid metal freezing in these thin channels, add sprues that feed metal to many points on the rim of a filigree mesh.

Thoroughly washing parts in 90%+ isopropyl alcohol (IPA) is critical to a clean casting. Excess uncured resin can interfere with investment curing and will cause casting defects.

Allow the parts to fully dry after removing them from the IPA bath. Use compressed air to ensure all IPA is fully evaporated prior to post-curing and casting. If parts are still sticky after washing and drying, you may need to replace your IPA.

For wash times, check out our support page. 

Post-cure will not improve casting results, unless parts are insufficiently washed. Parts may be optionally post-cured for extra handling strength if you experience parts breaking while spruing. If your parts are fragile, we recommend post-curing after support removal. Green parts are more flexible and less likely to shatter as you snip supports. Remaining touch tips can be sanded with 1,000 grit sandpaper after post-curing. 

For post-cure times and settings, check here for Form Cure V2, and here for Form Cure V1. 

Attach the post-processed prints to a main wax sprue with sticky sprue wax. Melt the wax to create smooth junctions between each printed pattern and its feed sprue.

Arrange thicker parts at the bottom and thinner parts at the top of the tree. 3D printed parts may require slightly more space between parts than a traditional wax tree. If you are casting large “thin-shelled” parts, make sure to fill any drain holes with wax to prevent any investment material from entering the print.

Formlabs does not recommend dipping 3D printed patterns into a “casting barrier” film. Casting barrier films may interfere with the ability of the resin to lose liquid wax during heating.

The following steps are a standard procedure for preparing any investment flask mold. A vacuum investing machine helps to evenly mix, degas, and pour the investment easily and cleanly. However, it is also possible to use a separate mixer and vacuum chamber.

Formlabs recommends Certus Prestige Optima jewelry investment for True Cast Resin, Castable Wax 40 Resin, and Castable Wax Resin. Castable Wax 40 Resin will give you more freedom in investment materials. If you are casting especially difficult designs, consider upgrading to a stronger phosphate bonded investment material, such as Nobilium Microfire. When using alternative investments, incorporate the manufacturer’s burnout recommendations.

Place the casting flask in the burnout oven and heat using the recommended Burnout Schedule. Make adjustments depending on the investment instructions, flask size, and amount of printed material.

Formlabs recommends using a well-ventilated furnace (with an inlet and an outlet), to provide sufficient air flow throughout the chamber and to safely exhaust all vaporized resin material.

Significantly shorter burnouts (four to eight hours) are limited to lightweight geometries and strong phosphate-bonded investment materials. Phosphate bonded investment will allow for a faster burnout with all Formlabs casting resins.

Tips:

• Venting is essential, but it can cause the temperature in the oven to drop. Monitor the oven and flask temperature and adjust your process as you develop a burnout schedule suited to your own equipment.
• If using active ventilation, increase suction as much as possible to improve airflow throughout the oven.
• If the oven is full, burnout will be less effective per flask. Attach an oxygen generator or low flow air line to the oven to increase the airflow.

Remove the mold from the furnace and cast metal. Centrifugal or vacuum casting machines such as the Neutec J2R (USA) and the Indutherm MC-series (EU) are simple to use and highly controllable. After casting, carefully quench the mold in water and wash away the investment.

Formlabs has tested gold, silver, and bronze castings from True Cast Resin, Castable Wax 40 Resin, and Castable Wax Resin patterns. Metal compatibility is foremost a property of the investment. Different metals require varying degrees of temperature resistance from the investment.

Formlabs direct-casting resins require temperatures of at least 732 °C to complete burnout. Ask the manufacturer if you are unsure about resin compatibility with a specific investment.

Formlabs offers True Cast Resin, Castable Wax 40 Resin, and Castable Wax Resin for jewelry investment casting. Castable Wax 40 Resin is designed to offer improved flexibility in its burnout schedule, and is more forgiving if you are new to casting resin. Castable Wax Resin requires stricter adherence to burnout guidelines and geometry limitations to achieve high quality casting results.

Recommended schedules for each material are shown below, for use with Certus Prestige Optima or equivalent investment.

View a full breakdown of times and temperatures based on investment and metal in our guide to using True Cast Resin here. 

Formlabs SLA 3D printers' seamless print process, high accuracy, and smooth surface finish allow you to move directly from design to production. Whether you are 3D printing try-on pieces for customers, ready to cast custom jewelry, or masters for reusable jewelry molds, Formlabs offers a material up to the task. Explore Formlabs SLA 3D printers to learn more, or contact sales to find the right solution for your application. 

Special thanks to Lars Sögaard Nielsen and the KEA (Copenhagen School of Design and Technology) for letting Formlabs document their casting process.