Both Reaction Injection Molding and Urethane Casting offer a good deal of design freedom, including the ability to mold-in features and encapsulate materials. They differ in the fact that only RIM allows for part design with significant wall thickness variations—typically from .125″ to 1.125″ in the same part.
RIM as well as urethane casting can be used to encapsulate a variety of materials, from metals to electronics. Each also produce a high quality finish, and take paint, silk screening and texturing well for improved branding.
Urethane casting in silicone rubber molds is often the more cost-effective choice for small production volumes, but rubber molds have a limited cycle life and long-term production can become cost prohibitive compared to RIM. Both processes are appropriate for producing molds for quick turnaround.
The initial tooling costs of urethane casting are lower than that of RIM. Tooling modification is also very cost-effective, but when aiming for production parts, RIM becomes the better choice cost-wise.
OTHER DESIGN CONSIDERATIONS: Many companies utilize rubber molds for years prior to converting to more permanent tooling, which can end up being extremely expensive. Because RIM can bridge the gap between prototype and production with parts that are precision molded instead of fabricated or cast, it can actually be most cost effective to utilize RIM in lieu of rubber molding.