Urethane castings is suitable for many uses but is primary application is the creation of high-detail short-run production pieces made from RTV molds. While urethane casting is a low cost alternative to producing detailed plastic injection molded parts.
It is similar to injection molding. During the process of injection molding, a hard tool is created. The hard tool, made of an A side and a B side, forms a void within and that void is injected with plastics ranging in material property, durability, and consistency.
Casting urethanes is similar in that polyurethanes are injected into a tool. But this tool is a soft tool, typically made with a type of silicone mold. The mold is created via a master pattern. While the master patterns can be created with CNC machining, or 3D printing.
FRY pictures below: