With urethane casting, parts can be created quickly and cost efficiently compared to hard tooling. It is well suited for smaller volume runs, serving as a resource for development, testing a product design, and conducting market research for consumer response. A main benefit of the process is the variety of properties, qualities, and color variations that can be created with urethane. Different types of urethane can be used in the same mold – hard or soft, clear or tinted – providing variety in use. The range of urethane properties allows for flexibility in testing throughout the development process and can help simulate materials such as glass or lenses.
To begin, a master pattern part is created from a CAD model using a variety of processes including CNC machining, CNC turning, 3D printing or hand sculpting. The master is used to create a mold, typically made of silicone. For soft parts, like foams, a harder material such as tooling board is used to create the mold.
For a silicone mold, the master is placed into a mold box, a part line is created for alignment, and the mold is filled with catalyzed liquid silicone. The process is repeated for the second side of a simple A and B side mold. After the mold is cured, it is split, the master is removed, and the result is a void the size and shape of the desired part. Gates or pathways are cut into the mold in order to allow urethane to fill the space and air to escape. To fill the mold, urethane is chosen, prepped, and degassed then injected into the mold. Once set, the part is removed from the silicone, trimmed, finished, and ready for assembly.