Cast Urethane Technology - Kehui Mold Co., Limited

Definition and Core Concept of Cast Urethane

Cast Urethane (also known as urethane casting or polyurethane casting) is a manufacturing process that involves pouring liquid polyurethane resin into a mold and allowing it to cure. It falls under the category of soft tooling and bridges the gap between traditional injection molding and 3D printing, making it ideal for low-volume prototyping and production parts.

How It Works:

Material Options: Two-component polyurethane resins (e.g., PU-85A, PU-70D) can mimic the properties of ABS, PP, rubber, and other engineering plastics.
Process Nature: Cures at room temperature or with mild heating, eliminating the need for high-pressure equipment (unlike injection molding).
Mold Requirements: Typically uses silicone molds or simple aluminum molds, significantly reducing costs compared to steel molds.

The Cast Urethane Process Workflow

Master Pattern Creation

A high-precision master model is made via CNC machining or 3D printing (e.g., SLA/DLP).

Silicone Mold Fabrication

The master is placed in a mold frame, and liquid silicone is poured around it. Once cured, the mold is split to remove the master.

Polyurethane Casting

The master is placed in a mold frame, and liquid silicone is poured around it. Once cured, the mold is split to remove the master.

Curing & Post-Processing

Room-temperature curing (2-24 hours) or heat-assisted curing is followed by demolding, trimming, and finishing (e.g., sanding, painting).

Comparison with Injection Molding

Parameter	Cast Urethane	Injection Molding
Tooling Cost	Low (200–200–2,000 for silicone)	High (5,000–5,000–50,000+ for steel)
Lead Time	1–3 days (including mold making)	4–8 weeks (for steel molds)
Per-Unit Cost	Moderate (best for <500 parts)	Very low (economical at >1,000 parts)
Material Properties	Near-engineering plastics (lower heat resistance)	Matches standard plastics (e.g., ABS/PC)
Surface Finish	Up to Ra 0.8μm (depends on master)	Excellent (polished/mirror options)

Typical Applications

Curing & Post-Processing

Produces working prototypes for testing form, fit, and function before committing to expensive steel tooling.

Low-Volume Production (50–500 units)

Ideal for crowdfunding campaigns, medical device trials, and other fast-to-market needs.

Multi-Material Simulation

Adjusting urethane formulations can replicate rubber (Shore A 40), rigid plastics (Shore D 80), and more.

Complex Geometries

Suitable for parts with undercuts, thin walls, or fine textures (silicone molds allow flexible demolding).

Limitations

Dimensional Accuracy: ±0.2mm (compared to ±0.05mm for injection molding).
Heat Resistance: Typically <80°C (special formulations may reach 120°C).
Mold Life: Silicone molds last ~50–200 cycles.
Labor-Intensive: Requires skilled operators for consistent quality in pouring and demolding.

Related Industry Terms

Rapid Tooling: Cast Urethane is a cost-effective soft tooling solution.
Vacuum Casting: An advanced Cast Urethane variant that minimizes bubbles via vacuum degassing.
Bridge Tooling: Interim production method while awaiting final steel molds.

When to Choose Cast Urethane?

Ideal For:

10–500 units of medium-quality plastic parts
Tight budgets and rapid timelines
Material properties close to engineering plastics

Not Suitable For:

High-volume production (>1,000 units)
Extreme heat (>120°C) or chemical exposure
Ultra-tight tolerances (e.g., gear mechanisms)

Future Trends

Advancements in material science are expanding Cast Urethane’s capabilities:

High-temperature urethanes (120–150°C)
UV-curable formulations (faster curing)
Hybrid 3D-printed molds (reducing silicone mold costs)

For product development teams, Cast Urethane remains indispensable in the “prototype-to-low-volume” transition, offering a low-risk pathway to validate designs before mass production.