When should engineers choose urethane casting instead of CNC or injection molding?

Volume, Lead Time, and Cost Considerations

Engineers should choose urethane casting primarily when bridging the gap between prototyping and mass production. For low volumes (typically 10-50 parts), Urethane Casting offers a significant cost advantage over injection molding, as it avoids the high expense of hard steel tooling. Its lead time is also considerably shorter—often days or weeks compared to months for machining and qualifying a production mold. While CNC Machining is ideal for single, high-precision prototypes, its cost per part remains high and does not decrease significantly with quantity, making it less economical than urethane casting for small batches.

Geometric Complexity and Design Flexibility

When a part features complex geometries, undercuts, or intricate textures that would be challenging or impossible to machine from a solid block, urethane casting is superior to CNC. The flexible silicone molds used in casting can easily release from these features without the need for complex, multi-axis machining paths or expensive tooling side-actions required in injection molding. This makes it an excellent choice for parts that consolidate assemblies into a single unit or require encapsulated components. It provides unparalleled design flexibility during the prototyping and low-volume manufacturing phases.

Material Properties and Final Part Requirements

Urethane casting should be selected when the functional prototype needs to closely mimic the material properties of a final injection-molded plastic part, such as flexibility, impact resistance, or transparency. While CNC is limited to the properties of the purchased plastic stock, cast urethanes can simulate a wide range of engineering-grade thermoplastics and elastomers. However, for parts requiring the specific high-temperature or chemical resistance of metals, or for very high-volume mass production, processes like Aluminum Die Casting or injection molding become the necessary and more economical choice.