[3D Printer] Industrial Precision Casting Using SLA 3D Printed Models

What Is Investment Casting (Precision Casting)?

Investment casting (also known as lost-wax casting) is a precision casting technique for producing complex metal parts. It is widely used for lightweight automotive components, golf clubs, jet turbines, industrial impellers, and artistic sculptures, enabling geometries difficult to achieve with traditional machining and offering excellent surface quality and high part integrity.

Traditional wax patterns usually require CNC machining to create molds, followed by wax injection. This process requires specialized equipment, multiple steps, and skilled labor, leading to high tooling costs and long lead times, making it unsuitable for rapid prototyping, one-off production, or small batch runs.

How Does 3D Printed Investment Casting Reduce Lead Times and Costs?

Using SLA 3D printing to create expendable sacrificial patterns eliminates the need for mold fabrication and wax injection. Patterns can be manufactured directly from a digital file, making it ideal for rapid delivery, custom parts, design validation, and small-batch casting, while freeing up CNC equipment and skilled operators.

SLA technology offers fine feature reproduction, excellent dimensional accuracy, and a smooth surface finish, accurately transferring pattern surfaces and features to the final metal part. Compared to traditional wax patterns, 3D printing allows for easier creation of undercuts, curved channels, thin-walled structures, and complex internal geometries.

The Formlabs SLA ecosystem is easy to set up, operate, and maintain, allowing for seamless integration of printing, washing, and post-curing into existing foundry processes.

Clear Cast Resin Material Properties and Casting Tests

Clear Cast Resin is an antimony-free, low-ash material with an ash content of less than 0.02%. Formlabs partnered with the University of Northern Iowa's (UNI) Foundry 4.0 Center and various industrial, service, and art foundries to validate its dimensional accuracy, surface quality, burnout effectiveness, and part costs.

Partner foundries used this process to cast bronze, brass, A356 aluminum alloy, Ti-6Al-4V titanium alloy, 4140 steel, 8620 steel, 316 stainless steel, and 17-4 PH stainless steel. Test patterns were burned out in furnaces at 700°C–900°C without autoclaves. Many patterns were attached to standard wax sprues, and ceramic shells were created according to each foundry's existing processes.

A356 Aluminum Alloy Investment Casting Case Study

At UNI Foundry 4.0, patterns were built with a tetrahedral lattice using Materialise's lattice module, employing a 0.5 mm lattice wall thickness and a 1 mm lattice diameter. These were printed on a Form 3L with a 100 μm layer thickness, and washed and post-cured following Formlabs' standard procedures.

Patterns were attached to a standard sprue using adhesive wax. A 100% silica-based ceramic shell system was used, with Remet RP-1 for the primary (first layer) sand and RG-1 for the backup (subsequent layers) sand, typically consisting of two primary layers and three backup layers. Stuccoing was performed after the second primary layer and after each subsequent dip. An automated system ensured coating uniformity, and the production time for a single tree was approximately 9–10 hours.

1. After the ceramic shells dried, they were flash-burned out at 900°C (1650°F) for two hours.
2. After cooling, the ceramic shells were moved to the casting area.
3. The ceramic shells were preheated to 540°C before pouring.
4. Aluminum alloy was poured at 700°C–750°C.
5. After the metal solidified, the main shell was knocked off, and residual ceramic was removed by sandblasting.

"The main reason we bought our Form 3L was the cost of patterns. We used to make impellers with traditional wax injection molds, which was difficult and time-consuming. When we switched to PMMA prints, the cost of a single pattern exceeded $300."

John Farr, Diversified Metal Fabricators

"Thanks to the Formlabs system and Clear Cast Resin, we can now produce high-precision patterns for art casting more quickly and consistently. Labor costs are a fraction of traditional hand-carved wax patterns, and we can quickly expand production capacity by adding equipment."

Julian Musi, Digital Atelier

Clear Cast Resin Test Results and Cost Analysis

Feedback from partner foundries indicates that 3D printed patterns in Clear Cast Resin can produce investment cast parts with quality comparable to traditional wax patterns. Printed patterns can be more brittle than wax patterns, requiring careful handling during assembly and tree building. However, after burnout, no significant ash residue was observed in visible areas of the ceramic shell, and no abnormal defects were found in the final metal parts.

Directly printing sacrificial patterns eliminates the need for molds, soluble wax cores, and other complex wax molding techniques, enabling the production of undercuts, curved channels, and thin-walled structures that are difficult to achieve with wax injection.

Overview of the 3D Printed Investment Casting Process

The following methods summarize real-world feedback from over 10 foundries, covering sacrificial pattern design, SLA printing, post-processing, tree building, ceramic shell creation, pattern burnout, and metal pouring.

Step 1: Designing a Hollow Lattice Sacrificial Pattern

Sacrificial patterns need to be strong enough to withstand ceramic slurry and handling pressures, while minimizing material volume to ensure smooth combustion, burnout, and reduced ash residue. Instead of printing solid, thick-walled patterns, a combination of thin outer walls and an internal lattice structure is recommended.

You can hollow CAD models and build internal lattices using precision casting tools in Materialise Magics or other software. Lattice settings allow control over shell thickness, internal support size, and drain hole placement.

Setting the Model's Outer Shell Wall Thickness

A thin outer wall minimizes thermal expansion and material residue during burnout, but can reduce print success rates and handling strength. Formlabs recommends starting with a 0.5 mm wall thickness and only increasing it if print failures or insufficient dimensional accuracy occur. Maintain a detail size of 0.5 mm initially.

Setting the Internal Lattice Structure

Lattices reinforce the pattern's outer walls, prevent warping, and support thin-walled prints. While thicker lattice struts increase strength, they also increase the risk of ceramic shell cracking due to material expansion. It is recommended to start testing with a strut diameter of 0.75 mm and a strut length of 3 mm.

Adding Drain Holes and Vent Holes

Drain and vent holes reduce suction effects during printing, allow uncured resin inside the model to drain, and improve airflow during combustion. Before designing holes, first determine the print orientation.

1. Place holes at the highest and lowest points relative to the print orientation.
2. Prioritize placing holes on sacrificial surfaces such as gates, where they can be cut or post-processed.
3. Start with a minimum hole radius of 1 mm and enlarge as appropriate if it does not affect critical surfaces.
4. Use straight holes (r1 = r2) or slightly chamfered holes (r1 > r2).
5. Place vent holes near gates to improve oxygen flow during burnout.
6. If the lattice model file size is large, export it in 3MF format to reduce file size and speed up support generation.

Step 2: 3D Printing with Clear Cast Resin

Step 3: Sealing, Tree Building (Assembly), and Pattern Preparation

1. Seal drain and vent holes using standard casting wax or a UV resin pen.
2. If using a UV resin pen, cure it completely according to the instructions.
3. Blow low-pressure compressed air into one of the holes as an inlet to check that all other holes are completely sealed.
4. Position gates, branches, and patterns according to your existing process for tree building.
5. Secure patterns to the wax tree using adhesive wax and place a T-bar suitable for dipping.
6. Standard wax sprues can be used, or sprues can be integrated into the 3D printed pattern.

For one-off production, ultra-small batches, or parts with extremely tight deadlines, adding extra ventilation channels to the pattern can improve airflow during burnout and increase the success rate of the first prototype. After burnout, cool the ceramic shell and repair vent holes using investment material or similar.

Step 4: Creating the Investment Casting Ceramic Shell

Once tree building is complete, create the ceramic shell according to the foundry's existing slurry and stucco (sanding) process. Some foundries use slurries with larger thermal expansion tolerance or increase the number of dips to reduce the risk of cracking, but Formlabs recommends first testing with existing standard processes.

UNI uses an automated robotic cell for six dips:

1. Dip once in a primary slurry without sand to maintain surface quality.
2. Dip once in backup slurry and apply primary sand.
3. Repeat three more dips with backup slurry and backup sand to increase shell thickness and strength.
4. Finally, dip once in a primary slurry without sand to form a sealing layer.

Step 5: High-Temperature Burnout of 3D Printed Sacrificial Patterns

Burn out the patterns in a high-temperature furnace according to the foundry's usual procedure. Typical flash burnout conditions are 705°C–900°C (1300°F–1650°F) with a hold time of approximately two hours. The furnace must maintain high temperatures and supply sufficient oxygen to completely burn off the patterns.

After burnout, check the ceramic shell for cracks or burrs and remove any internal ash residue. Clear Cast Resin is antimony-free and has an ash content of less than 0.020%. Combined with a hollow lattice design, this minimizes residual ash.

Step 6: Metal Pouring and Casting Finishing

Once the pattern burnout and ceramic shell inspection are complete, you can proceed to the existing metal casting and finishing processes. In UNI's case, the following steps were taken:

1. Preheat the ceramic shell in a holding furnace at 345°C (650°F) for 30 minutes.
2. Pour the metal and allow it to cool and solidify completely.
3. Remove the ceramic shell using high-pressure washing (water jet) or sandblasting equipment.
4. Carefully remove partial shell if necessary, using tools like chisels to avoid damaging the casting.
5. Cut the parts from the tree using a band saw or appropriate cutting tools.
6. Perform machining, grinding, blasting, or other finishing operations as required by the part.

Summary of Clear Cast Resin and 3D Printed Investment Casting

With Clear Cast resin, foundries can produce lost patterns directly from digital data, eliminating the need for traditional mold making and complex wax molding processes. This makes it ideal for rapid prototyping, quick turnaround times, custom parts, and small-batch investment casting.

This workflow also enhances design freedom for undercuts, tortuous channels, thin walls, and complex geometries. Manufacturers can produce patterns on demand, deferring investment in hard tooling while validating designs with actual metal parts before committing to mass production tooling.

Case study results show that by adopting Formlabs SLA equipment and Clear Cast resin, some existing processes can be adjusted to significantly reduce pattern and tooling costs for specific projects and shorten lead times from weeks to months. The actual cost-effectiveness must be evaluated individually based on the part, production volume, materials used, and casting conditions.