Investment casting is a foundry process for producing metal parts with intricate shapes that cannot be manufactured in other ways. Using Formlabs Clear Cast Resin, you can produce parts right away without tooling, soluble cores, or other complex wax formation techniques. Features like undercuts, channels, and thin walls that are difficult to pattern for wax injection are easy to 3D print.

Clear Cast is designed to work for larger molds, generally where the wall thicknesses are greater than ⅛ inch or 3 mm thick across the majority of the part. It requires latticing and drain holes to function properly, as a solid part is extremely likely to crack shells.

Clear Cast Resin prints at 50 and 100 microns.

When choosing a casting resin, take the casting properties of each material into consideration. For smaller parts or wire filigree, use Castable Wax Resin. For medium to heavy jewelry or small engineering components, use True Cast Resin. For larger investment casting, use Clear Cast Resin.

Sacrificial patterns for industrial investment casting must be strong enough to withstand the pressure of being dipped in ceramic slurry while also being thin enough to burn away. Thin walls prevent cracking caused by thermal expansion during burnout. Software solutions are available that hollow the part and build inner lattice scaffolding to strengthen the part. The lattice supports the exterior of the part, prevents warping, and enables printing with thin walls. The sprue can also be 3D printed as part of the pattern. Since the lattice is required to create quality castings, it is recommended not to go below ⅛ inch or 3 mm for the majority of the part.

After designing the part with your CAD software, import the CAD file into the lattice module and determine the settings for the outer shell, the lattice structure, and drain holes. Thinner walls improve casting success, but they increase the risk of print failures and may weaken parts.

Print feature recommendations

Large, thick-walled parts

For larger parts that are intended to have thicker walls, you can hollow the walls as well for printing. For example, you could print a large statue with walls that are 5 mm thick in total, provided that you hollow and lattice the walls themselves with your latticing software.

Drain holes reduce the risk of print failures caused by cupping and allow liquid resin to drain out of the part.

• Keep the planned orientation of the part in mind when designing drain holes.
• Place holes near the extremes of parts, or along the edges to allow IPA and liquid resin to drain completely.
• Place holes at the top and bottom of the planned part orientation.
• Place holes on surfaces that will be machined or cut to simplify post-processing.
• Create straight holes (r1 = r2) or only slightly chamfered holes (r1 > r2).
• Place holes in the location where the sprue will be attached to allow for good airflow during burnout.

Latticed parts can result in large file sizes, which slow down the print preparation and support generation process. Convert your exported files to 3MF to reduce the file size.

Install or update PreForm, then set up the next print job.

To prepare a model for printing in PreForm:

1. Open a model.
2. Select the resin, resin version, and the desired layer thickness.
3. Follow Formlabs best practices for orienting parts. Orient the model 30-45 degrees relative to the build platform.
4. Generate supports.
   • Add a full raft, using 0.75 support density and 0.30 mm touchpoints or smaller. Avoid placing support touchpoints on critical surfaces.
   • Formlabs recommends turning off internal supports on latticed parts, as they may interfere with the lattice structure.
   • Due to their geometry, casting patterns frequently trigger PreForm warnings about being undersupported or having cups. Support minima on the skin of the part to minimize these warnings as much as possible.
   • You may wish to generate supports for a non-latticed pattern and match the supports on the latticed version to that.
5. Send the print job to the printer.

The Form Wash and other washing systems agitate the solvent bath and remove parts from the bath after a set time. Wash parts according to the support article for your device. Pay particular attention to information that affects mechanical properties or biocompatibility requirements.

After an initial wash, dry parts and clear the lattice structure using compressed air. Wash the part again and thoroughly clear it with compressed air, taking care to clear out as much IPA and resin as possible from the interior. Allowing IPA and resin to sit in the part may cause the shell to become floppy, making it unsuitable for casting.

Clear Cast Resin requires post-curing to reach its optimal mechanical properties. Follow Formlabs best practices when deciding whether to remove supports before or after post-curing. Refer to the support article for your device for post-curing recommendations.

Follow the instructions in the support articles Removing support marks and Advanced support removal techniques to post-process printed parts.

Patching drain holes

There are three main ways to patch drain holes:

• Wax: This is typically the easiest method but is sometimes prone to pinhole failures. This can also simply be done as attaching the drain holes to vents or gating that is otherwise necessary.
• Resin: Formlabs recommends placing a small amount of resin over the hole and using a UV pen to cure it. This typically creates solid coverings that are functionally the same as the rest of the part.
• Part design: You may wish to generate the hole patches as their own parts, print them, and then attach these to the parts, though this is typically unnecessary for parts without extremely large holes.

Check the fit of the holes by forcing compressed air into the last hole and looking for leaks.

Bonding multiple pieces

You have similar options for bonding multiple pieces together before casting if your design exceeds the build volume of your printer:

• Wax
• Resin: Apply liquid Clear Cast Resin to the seam and cure with a UV pen or gun. As with drain holes, this creates a solid connection that is functionally the same as the rest of the part.
• Casting-specific adhesives

Burnout

Follow your usual process for pattern assembly, shell creation, and burnout. For burnout, Formlabs recommends flash firing at a temperature of 1300–1650 °F (700–900 °C) for two hours. Do not use an autoclave to dewax parts as this can cause parts to expand, warp, and buckle, and will often crack shells. Check for any cracking or flashing in the shell after the burnout and blow out any remaining ash from the mold.

Follow your usual process for casting and finishing.