Ceramic Shell Casting with Resin 3D-Printed Patterns

How Resin 3D-Printed Parts Work in Ceramic Shell Casting

In ceramic shell casting, a wax pattern is dipped repeatedly into a ceramic slurry and sand to build up a hard outer shell. Once the shell is cured, the wax is melted / burned- out (the “lost-wax” principle), leaving a cavity that perfectly matches the desired part. Molten metal is then poured into this cavity. When using a 3D-printed resin part, the process is nearly identical, but the material used for the pattern must meet two critical criteria:

1. Accuracy and Surface Finish: 3D-printing resins can achieve the fine details and smooth surfaces required for precision casting.

2. Clean Burnout (Low Ash): Unlike standard resins, specialized castable resins are formulated to burn cleanly during the burnout phase, leaving minimal ash residue. Any leftover ash or residual material can contaminate the mold cavity, resulting in defects and imperfections on the final metal part. Low-ash resins ensure the ceramic shell is completely empty, clean, and ready for metal pouring.

This integration delivers significant benefits, including faster turnaround times (by eliminating tooling lead time), lower costs for small to medium batches, and design freedom for complex parts that would be impossible or cost-prohibitive with traditional methods.

Investment Casting With 3D Patterns: Process Overview

It is important to follow the processing guidelines as good as possible. These parameters are tested. Variations in these parameters might lead to insufficient strength of the part or a loss of surface quality in the final metal part. A combination of ash-free burnout resin, a good workflow for lost wax casting with resin will yield non-porous metal parts.

1. Pattern Design

Design the part in CAD software. It is necessary to hollow the part and build an internal lattice structure to aid in the burn-out process. In free software like Chitubox this can be done easily. Choose a wall thickness of 0,5mm (~0.0197 inches) and an infill of 5%. Finally choose the best orientation for the part and make a drain hole of 3mm (~0,12 inch) on the lowest and highest area of the part. The thin walls will help in an ash-free burn-out, while the lattice structure will support the thin walls from not collapsing during processing. The drain holes are needed so the part won’t be collapse during 3D-printing from the build-up pressure in hollow part.

2. Pattern 3D Printing

3D print the pattern using a specialized resin, such as Liqcreate Wax Castable, on any of the open resin 3D-printers that it is compatible with. Liqcreate Wax Castable is compatible with printers from $/€100 and onwards. Place the part in the slicing software, place supports and start printing!

3. Pattern Preparation

After 3D-printing, the parts need to be washed for at least 2x 3 minutes. If parts contain only 2 drain-holes, spend some extra time washing the inside of the hollow parts. This can be done by pouring washing solvent, IPA or ethanol in the drain hole and let it fill and empty a few times. Then let the part sit on your desk for at least 30 minutes prior to 30 minutes UV-curing.  After UV post-cure, fill any vents and drain holes using standard foundry wax or 3D-print resin with an UV-light. Then, follow your usual process for pattern assembly, attaching the printed parts with wax to a central sprue to form a casting tree.

4. Shell Making

Follow the standard workflow from R&R with its SuspendaSlurry® materials. SuspendaSlurry material was developed to eliminate costs associated with continuous mixing and to simplify the initial mixing process as the pre-mixed, chemically suspended ceramic shell slurry eliminates the need to weigh and mix binder and refractory components. Used for non-ferrous metals, SuspendaSlurry FS material is recommended for both initial and backup coats. Follow your usual process in the link above to dip the tree in the ceramic slurry, then coat it. This process is repeated several times until a sufficiently strong and thick ceramic shell is built up.

5. Pattern Burnout

Follow your standard burnout process, which typically involves placing the shell in a flash-fire furnace. A common technique is flash fire, which rapidly heats the parts to between 700 °C and 900 °C (1,300 °F and 1,650 °F) for two hours to enure the resin pattern completely burns away.

6. Casting

Follow your usual process to pour the molten metal (e.g., bronze, brass, aluminum, steel, or titanium) at the right temperature into the hot ceramic mold cavity.

7. Shell Removal

Allow the metal to cool and solidify. The ceramic shell is then removed using a water or sandblaster.

8. Cutting Off

Separate the final metal parts from the sprue/tree using a bandsaw or other cutting tools. The finished metal part then undergoes standard post-processing, such as grinding or machining.

Frequently asked questions

• – Q: What is the burnout temperature for Liqcreate Wax Castable?

  • A: Liqcreate Wax Castable resin needs a temperature of at least 700°C / 1300°F for a clean burn-out. A flash fire burn-out between 700 °C and 900 °C (1,300 °F and 1,650 °F) for two hours is recommended to enure the resin pattern completely burns away.

• – Q: Can I use standard resin for ceramic shell casting?

  • A: It is not recommended as it can leave residues, react with the investment material or has too much thermal expansion, which makes the shell crack. it is advised to use specialized 3D-printing resins like Liqcreate Wax Castable.

• – Q: How thick should the walls of the casting pattern be?

  • A: a wall thickness of 0,5mm (~0.0197 inches) and an infill of 5% works best for most parts. Finally choose the best orientation for the part and make a drain hole of 3mm (~0,12 inch) on the lowest and highest area of the part. The thin walls will help in an ash-free burn-out, while the lattice structure will support the thin walls from not collapsing during processing.