Lead time: It takes an average of two weeks for silicone tooling to be created. Once it’s done, however, parts can be produced quickly.
Short tool life: Silicone tooling can only produce an average of 20-25 parts. After that, new tooling must be built to produce additional castings. This also means that urethane casting isn’t practical for large-scale part production.
Limitations for prototyping: Additive manufacturing is ideal for rapid prototyping because it enables designers to quickly iterate a series of designs. In contrast, the silicone tooling used for urethane castings tends to lock engineers into a single design. New tools can be built to accommodate design changes, but each one takes an average of two weeks to build.
Impractical for 1-2 prototype parts: Compared to CNC machining or additive manufacturing, the cost to produce silicone tooling to produce one or two prototype urethane parts can be cost-prohibitive on a per-part basis. The sweet spot for producing urethane castings is in the 50-100 range.