Cast Urethane Molding: What It Is, How It Works, and Why It Matters
Cast urethane is a highly capable plastic molding process that fills the gap between 3D printing and high-volume injection molding. Cast urethane molding uses liquid polyurethane and flexible silicone molds to produce high-quality plastic parts in small quantities, delivering production-grade results without the high upfront cost and lead time of traditional tooling.
Whether you are validating a design, running a limited production batch, or bridging to injection molding, cast urethane can help bridge the gap.
Built for Low Quantity. Engineered for High Quality.
When timelines are tight or designs are still evolving, cast urethane delivers without forcing you to choose between speed, quality, and cost.
✔ Cost-Efficient Tooling: Silicone molds cost significantly less than steel or aluminum tooling, making it practical to iterate without the financial risk of committing to hard tooling early.
✔ Scalable Production: Ideal for quantities ranging from 10 to 500 pieces, making it the right fit for pilot programs, limited runs, and design validation.
✔ Material Flexibility: Polyurethane materials can be formulated across a wide durometer range, from rigid ABS-like parts to soft elastomeric components, with strong abrasion and impact resistance.
✔ Fast Iteration Cycles: Low-cost tooling means design changes can be incorporated quickly, making cast urethane ideal for market testing and bridging production before transitioning to injection molding.
How Cast Urethane Molding Works: A Step-by-Step Process
Here is a breakdown of each stage in the process, from master part preparation through final quality inspection.
Step 1: Master Prep
- The process begins with a master part, typically 3D printed, that serves as the template for the mold.
- Dimensions are checked and surfaces are smoothed to ensure accuracy.
- The master is primed with gray paint, and standoffs, screws, and cutting lines are added in preparation for the mold build.
Step 2: Mold Build
- A box is built around the master part to create the mold cavity.
- Silicone is mixed and poured around the master, then degassed in a vacuum chamber to remove trapped air bubbles.
- The mold is left to cure, producing a flexible, detailed negative of the master.
Step 3: Mold Prep
- Once cured, the mold is removed from the box and assembled with inserts, screws, and input/outlet tubes.
- The flexibility of silicone molds allows for complex geometries and undercuts that would be costly with hard tooling.
Step 4: Mold Fill
- The assembled mold is placed inside a VacuCast chamber.
- A two-part polyurethane mixture is injected under vacuum to eliminate air entrapment.
- The part is heat cured and allowed to cool to room temperature before demolding.
Step 5: Finishing
- The mold is opened and the part is carefully removed.
- Parts are sanded, trimmed, and shaped to meet dimensional requirements.
- Three coats of primer and paint are applied with drying time between each coat for a production-quality surface.
Step 6: Quality Check
- Every part is inspected using coordinate measuring machines (CMM) and hand tools to validate dimensional conformance.
- Approved parts are packaged and shipped.
Is Cast Urethane Right for Your Project?
If you are working on a design that is still evolving, planning a limited production run, or looking for a cost-effective bridge before committing to injection mold tooling, cast urethane may be exactly what your program needs.
At Innova Engineered Plastics, our team works with you from early concept through production-ready parts. With prototype lead times under four weeks and quantities from 10 to 500 pieces, we help product teams move faster without compromising on quality.
