In product development, there is a notorious “gap” known as the Valley of Death between prototyping and mass production.

If you need 1 part, you 3D print it. If you need 100,000 parts, you cut a steel mold for Injection Molding. But what if you need 30 units for a marketing launch? Or 50 units for beta testing?

3D printing is too slow and lacks the surface finish for end-use. Steel molds are too expensive and take weeks to manufacture.

The solution is Vacuum Casting (often called Urethane Casting). This process is the ultimate “bridge manufacturing” technique, offering production-grade quality at a fraction of the tooling cost. Here is why Vacuum Casting is the ideal choice for your low-volume needs.

What is Vacuum Casting? (The Process Simplified)

Vacuum casting uses a soft silicone mold to replicate a master pattern. Because the mold is flexible, it handles undercuts and complex geometries easier than rigid steel molds. The process follows a 3-step lifecycle:

1. The Master Model: We create a high-precision master pattern (usually via SLA 3D Printing or CNC machining) and hand-polish it to the exact surface finish required (e.g., Glossy, Matte, or Textured).

2. The Silicone Mold: Liquid silicone is poured around the master model in a casting box. Once cured, the mold is cut open, and the master is removed.

3. The Casting: Polyurethane resins are poured into the empty silicone mold inside a vacuum chamber. The vacuum ensures there are no air bubbles, resulting in a void-free, dense plastic part.

Technical Note: A single silicone mold typically lasts for 15 to 25 shots (copies) before the chemicals in the resin degrade the silicone surface. This makes it perfect for batches of 20–50 units.

Top 4 Advantages of Vacuum Casting

Low Upfront Cost (The Budget Winner)

The biggest barrier to entry for injection molding is the cost of the metal tool (Hard Tooling), which can range from $5,000 to $50,000.
In contrast, a silicone mold costs a fraction of that amount. While the per-unit price of a vacuum cast part is higher than an injection molded part, the total project cost for small quantities is significantly lower.

Production-Grade Aesthetics

Unlike FDM or SLS 3D printing, which leave visible layer lines, vacuum casting replicates the surface texture of the Master Model perfectly. If the master is polished to a mirror finish (SPI-A2), every single cast part will come out glossy. This makes the parts indistinguishable from mass-produced injection molded goods.

Material Versatility (The “Simulants”)

Vacuum casting resins are formulated to simulate the properties of engineering plastics. Whether you need the toughness of ABS, the clarity of PC, or the flexibility of Rubber, there is a resin for it.

Material Simulant Table:

Overmolding and Color Flexibility

Because the resin is mixed manually before pouring, we can add pigments to match Pantone or RAL colors exactly—no painting required. Furthermore, we can perform Overmolding, casting soft rubber grips over rigid plastic cores, a feature essential for handheld device prototypes.

Comparison: The Manufacturing Decision Matrix

When should you switch from 3D printing to Vacuum Casting? Use this comparison table to guide your decision.

The Verdict: Choose Vacuum Casting when 3D printing isn’t strong or pretty enough, but you aren’t ready to invest thousands in a steel mold.

Ideal Use Cases for Boona Clients

• Marketing Samples: Create 20 units for a trade show or photography. They look exactly like the final product.

• Beta Testing (EVT/DVT): Functional testing where material properties (snap-fits, heat resistance) must mimic the final production part.

• Medical Devices: Utilizing Boona’s ISO 13485 expertise, we produce small batches of medical housings that require specific fire-retardant (UL94-V0) or biocompatible-grade resins.

• Bridge Production: If your steel mold is delayed by 4 weeks, vacuum casting can provide 50 parts now to keep your assembly line running.

Technical Parameters & Design Guide

To ensure success with Vacuum Casting at Boona Prototypes, keep these design parameters in mind:

• Standard Tolerance: $\pm 0.15mm$

   per 100mm. (Note: This is slightly looser than CNC machining due to the shrinkage of the silicone and resin).

• Minimum Wall Thickness: 0.75mm to 1.0mm. (Large flat areas should be thicker to prevent warping).

• Max Part Size: Boona can cast parts up to approx. 1900mm x 900mm x 750mm (depending on mold weight).

• Draft Angles: Not strictly required! Because the silicone mold is flexible, we can often remove parts with 0° draft or even slight undercuts without sliders—a huge design advantage.

Conclusion

Vacuum Casting is the unsung hero of product development. It offers the “sweet spot” of speed, economy, and quality for low-volume production.

At Boona Prototypes, we handle the entire process under one roof—from CNC machining the master pattern to casting the final urethane parts. Whether you need a soft-touch rubber grip or a clear lens housing, our team ensures your short-run production meets strict quality standards.

Need 20 to 50 parts that look and feel like the real thing?

[Upload your CAD file to Boona Prototypes today] for a fast Vacuum Casting quote and expert material advice.

FAQs

Do you use real thermoplastics (like ABS or Polycarbonate) in vacuum casting?

No, vacuum casting uses polyurethane resins that are chemically formulated to simulate the properties of real thermoplastics. We call them “simulants.” For example, we use a resin that mimics the impact strength of ABS or the optical clarity of PC, but chemically, they are thermoset polymers, not thermoplastics.

Why can I only get about 20 parts from one silicone mold?

The chemical reaction of the polyurethane resin generates heat and attacks the surface of the silicone. After about 20 to 25 cycles (shots), the mold surface starts to degrade, become brittle, or lose its glossy finish. For quantities larger than 50, we simply make multiple silicone molds from the same master pattern.

Do I need to supply the Master Model myself?

No. Boona Prototypes offers a turnkey solution. You only need to provide the 3D CAD design. We will fabricate the Master Model in-house (usually via high-resolution CNC machining or SLA 3D printing) and finish it to your specified texture before making the mold.

Can vacuum cast parts be painted or color-matched?

One of the biggest advantages of vacuum casting is that we pigment the liquid resin before pouring. This means the part comes out of the mold already in your desired color (matched to Pantone or RAL codes). This is more durable than surface painting because the color goes all the way through the part, so scratches won’t show white underneath.

What is the difference between “Shore A” and “Shore D” in your material options?

These refer to material hardness. Shore A is for soft, rubber-like materials (e.g., Shore A 40 is like a pencil eraser; Shore A 90 is like a shoe heel). Shore D is for rigid, hard plastics (e.g., Shore D 80 is typical for hard ABS-like housings). We can cast both types.

What tolerances can I expect?

Vacuum casting is generally less precise than CNC machining due to the shrinkage of the silicone mold and the resin itself. We typically hold a tolerance of ± 0.15mm per 100mm. For features requiring extremely tight tolerances (like bearing bores), we recommend post-machining the cast part via CNC.

Is vacuum casting suitable for outdoor use?

Yes, provided the correct resin is selected. Many standard resins can yellow under UV light over time, but we offer specific UV-stable grades (like PX 5210) that are designed for outdoor applications or automotive lighting components.

How does the cost compare to 3D printing?

For 1 part, vacuum casting is expensive because you must pay for the Master and the Mold. However, the “breakeven point” is usually around 5 to 10 units. Once you need more than 10 parts, vacuum casting becomes significantly cheaper per unit than SLA/SLS 3D printing, with much better surface quality.