Urethane casting is a manufacturing process in which a liquid urethane material is injected into a silicone mold, post cured in an oven, and then the desired plastic part is removed from the mold. Secondary processes can also be performed on the molded part if desired. Urethane casting is good for low-volume parts and prototypes, as the silicone mold will typically only cast about 20-25 parts. Its big advantage over other plastic part manufacturing processes like injection molding is that the silicone mold is made quickly and relatively inexpensively compared to hard tooling.
The first step in the casting process is to create the mold from a “master pattern.” Master patterns can be created by CNC machining, additive manufacturing (3D printing), or by using an already existing product. The pattern is then encased in quick-curing liquid silicone to form a cavity within the mold, which will be used to form the urethane part. After the mold cures, it is cut in half and the pattern is removed. The cavity formed by the master pattern is then used for casting the end product.
The silicone mold material is good for picking up surface detail, so it will duplicate the surface finish of the master pattern onto the parts. The finished dimensions of the urethane cast parts depend on the accuracy of the master model, part geometry and casting material.
Since vacuum, heat and pressure are applied in the casting process, the result is a strong, stable, void-free part. For this reason, urethane casting is a good choice for producing high-quality, precise and consistent parts, fast. With all these advantages, the one thing that must be remembered is that this is a process for producing low-volume or prototype parts, as the molds are not durable enough for very many uses.
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