Vacuum Casting FAQ

Vacuum Casting, frequently referred to in the industry as Urethane Casting or RTV Molding (Room Temperature Vulcanization), is a rapid manufacturing process used to create high-fidelity plastic and rubber parts. Unlike 3D printing, which builds layers, vacuum casting uses a silicone mold to replicate a master pattern. The process is performed under a vacuum to remove air bubbles, resulting in parts with smooth surfaces and dense material properties that closely mimic Injection Molding.

The process involves three critical stages:

1. Master Pattern Creation: We create a perfect master model using CNC Machining (for high precision) or SLA 3D Printing (for complex geometry). This master is hand-finished to your desired surface texture.

2. Silicone Mold Making: Liquid silicone is poured around the master pattern in a casting box. Once cured, the mold is carefully cut open, and the master is removed, leaving a negative cavity.

3. Part Casting: Polyurethane (PU) resin is poured into the silicone mold inside a vacuum chamber. The vacuum pulls the resin into every detail and eliminates bubbles. The part is then cured in an oven.

They are completely different.

• Vacuum Casting (Urethane): Pours liquid resin into a mold to make solid 3D parts (like a drill housing).

• Vacuum Forming: Heats a plastic sheet and sucks it over a mold (like a blister packaging or yogurt cup). Boona specializes in the former (Urethane Casting).

Because the mold is made of silicone rubber, which is soft and flexible. This is in contrast to “Hard Tooling” (Steel) used in mass production. The flexibility of silicone allows us to mold parts with undercuts and negative drafts without complex sliders, reducing cost and lead time.

A single silicone mold is not permanent. It typically lasts for 15 to 25 shots (parts) before the chemical reaction with the resin degrades the mold surface or dimensions start to drift. If you need 100 parts, we will create approximately 4-5 silicone molds from the same master pattern to ensure every part meets the spec.

You should switch from 3D Printing to Vacuum Casting when:

• Quantity: You need 10-100 identical parts. Printing them one by one is too slow and expensive.

• Surface Finish: You need a smooth, cosmetic finish (no layer lines) straight out of the mold.

• Material Performance: You need specific properties like rubber elasticity (Shore A), high heat resistance, or transparency that 3D printing filaments cannot perfectly match.

It depends on volume.

• Low Volume (20-100 units): Vacuum Casting is cheaper. A silicone mold costs hundreds of dollars, while a steel mold costs thousands.

• Mid-High Volume (500+ units): Injection Molding is cheaper. The unit price of injection molding is much lower.

• Strategy: Use Vacuum Casting for “Bridge Production” (market testing) while waiting for your production steel molds to be manufactured.

Speed is our advantage.

• Master Pattern: 2-3 days.

• Mold Making: 1-2 days.

• Casting: We can typically cast 4-6 parts per day per mold. For a batch of 20 parts, the total turnaround is usually 7-10 days. This is weeks faster than cutting steel tools.

No. You only need to provide the 3D CAD design (STEP/IGES files). Boona will manufacture the master pattern in-house to ensure it meets the necessary shrinkage compensation and surface finish requirements.

(Hei-Cast / Axson) We use high-grade Polyurethane (PU) resins that simulate the properties of engineering thermoplastics. We source materials from premium suppliers like Hei-Cast (Japan) and Axson. Common types include:

• ABS-like: (e.g., PX-200, 8150) High impact strength, good for housings.

• PC-like: (e.g., PX-5210) Clear, high strength, UV stable.

• PP-like: (e.g., UP-5690) Flexible, high elongation, good for snap-fits.

• High-Temp: Resins resistant up to 130°C. View our full Material List.

 Yes, this is a core strength of Vacuum Casting. We can cast rubber parts with precise hardness levels ranging from Shore A 30 (soft, rubber-band like) to Shore A 90 (hard, hockey-puck like). It is the best method for prototyping gaskets, seals, buttons, and overmolds.

Yes. We use PMMA-like resins (such as Hei-Cast PX-5210).

• The Process: We polish the Master Pattern to a high-gloss mirror finish (SPI-A2). The silicone mold replicates this smoothness perfectly. The vacuum process ensures zero air bubbles.

• Result: A part that looks like clear acrylic or glass, suitable for light pipes and lenses.

Yes. We can cast parts using flame-retardant resins (e.g., Hei-Cast 8150 FR) that comply with UL94 V-0 standards. This is essential for electronic enclosures and automotive components.

We have “Bio-compatible capable” resins that simulate USP Class VI materials. However, for strict FDA clinical trials or long-term food contact, vacuum casting resins are generally not recommended. For these applications, we suggest CNC Machining in Medical PEEK or Food-grade PP.

Our vacuum chambers can accommodate molds roughly 1000mm x 600mm x 500mm. For parts larger than this (e.g., a full car bumper), we recommend splitting the part into sections, casting them separately, and bonding them together (glue welding), or using large-format CNC.

Vacuum casting is precise, but depends on thermal shrinkage. We generally follow ISO 2768-m (Medium).

• Rigid Parts: ±0.15% of the dimension or ±0.15 mm.

• Rubber Parts: ±0.3 mm (due to material flexibility). See our Quality Control standards for more details.

Ideally, Yes (0.5° – 1°). However, one of the biggest benefits of silicone molds is their flexibility. We can often demold parts with Zero Draft or even minor undercuts without needing complex tooling mechanisms. This gives designers more freedom than injection molding.

 Yes. The silicone mold can be manually stretched or flexed to release undercuts. For deep or complex undercuts, we create specific “Mold Inserts” (also made of silicone) that are removed with the part and then put back into the mold for the next shot.

• Minimum: 0.75mm (to ensure proper flow).

• Recommended: 1.5mm to 3.0mm.

• Warning: Avoid extremely thick sections (>10mm) as they can cause shrinkage (sink marks) or curing issues. If thick sections are needed, we recommend coring them out.

Yes, and it is much cheaper than injection molding. We can cast a rigid substrate (e.g., ABS-like) first, place it into a second mold, and then cast a rubber material (Shore A) over it. This creates a chemical and mechanical bond, perfect for Soft-Touch Grips on handheld devices.

Yes. We can manually place threaded brass inserts (Knurled nuts), steel bushings, or even electronic components into the mold before pouring the resin. The resin cures around the insert, holding it securely.

 Yes. We mix pigment into the liquid resin before pouring. We can match Pantone C and RAL codes. Since the color is integral (all the way through the part), scratches won’t show a different color underneath.

 Yes. The texture comes from the Master Pattern. We can apply Mold-Tech textures, VDI 3400 EDM finishes, or simple sandblasting to the master. The silicone mold replicates every microscopic detail of that texture onto the cast parts.

Since plastic resins are non-conductive, we can apply Conductive Paint (Copper or Nickel) to the interior of the cast enclosure. This provides electromagnetic shielding for your prototypes to pass compliance testing.

Like injection molding, liquid PU resin shrinks slightly when it cures (turns solid). Our engineers calculate this rate (usually 0.15% – 0.25%) and enlarge the Master Pattern to compensate.

Standard resins are sensitive to UV light. However, Boona uses UV-stabilized resins (like PX-5210) and we can apply a UV-protective Clear Coat (painting) to prevent yellowing, ensuring your prototype looks fresh for years.

Yes. We use specific “PP-like” resins (e.g., UP-5690) that have high elongation properties. These can withstand repeated bending without snapping, making them suitable for functional prototype containers.

It varies by size, but generally ranges from $300 to $800. Compared to a $5,000+ steel mold, this low entry cost is why Vacuum Casting is the king of low-volume production.

Silicone molds have a short shelf life. They become brittle and shrink over time (even if not used). We usually keep them for 30-60 days. If you re-order 6 months later, we will likely need to cast a new silicone mold from the original Master Pattern.

Yes. This is common. You can order 20 units of the Top Case (ABS-like) and 20 units of the Keypad (Rubber Shore A 60). We manage the assembly as part of our One-Stop Service Solution.

It’s simple. Upload your 3D files (STEP/STP/IGES) to our Get a Quote page.

• Important: Please specify the Quantity and the desired Material Property (e.g., “I need it to feel like ABS” or “I need Shore A 70 Rubber”).

Absolutely. We work with global clients on sensitive product developments. We are happy to sign an NDA (Non-Disclosure Agreement) before receiving your files. Your data is stored securely and never shared.

Yes. We ship daily to the USA, Europe, and Australia via DHL, FedEx, or UPS. Vacuum cast parts are lightweight, so air shipping is usually fast and affordable.

We perform 100% visual and dimensional inspection before packing. If a part has bubbles, warping, or is out of tolerance, we will remake it for free. Boona stands behind our quality.

• Shore A 30-40: Very soft (Mouse pad gel, rubber band).

• Shore A 60-70: Medium (Car tire, shoe sole) – Most common for gaskets.

• Shore A 90: Hard (Shopping cart wheel, hard hat).

• Shore D: Hard plastics (ABS, PC).