Urethane casting, also known as polyurethane casting, is a resin casting production process used for casting components made from urethane materials. The process uses temporary polymer molds that are produced from a master pattern or part. This type of casting is a popular process used for the rapid prototyping of components, especially in cases where the production material is not suitable for rapid prototyping. Urethane is chosen for this process mainly because it is a cost effective option and offers material choice for matching the production materials’ mechanical properties. In addition, by using urethane castings, manufacturers are also able to duplicate their production parts with detailed precision. Drift angles and under cuts are easily reproduced due to the flexible nature of the mold. The molds that are used for the production of the castings are usually made from RTV (room-temperature vulcanization) silicone.
This prototyping process creates urethane parts with size, form, as well as properties similar to the production parts. Using this method, manufacturers can economically produce multiple urethane prototypes of their components, which can be used for various purposes, including sales and marketing, focus groups, and as early part samples for customers. Apart from these applications, urethane castings can also be used for testing prototypes. It should be noted that urethane cast parts are not ideal substitutes for tests where the production materials play a significant role, such as failure mode testing and life testing of components. However, in many cases urethane materials that have properties similar to the production material, can be used for these tests.
The urethane casting process begins with the production of a master pattern or part, from which the molds and eventually the castings are produced. A number of methods, including conventional machining, can be used to produce this master pattern. However, the most common method of producing the master pattern is by stereolithography (SLA) – an additive production process that involves using a UV-curable photopolymer resin in combination with a UV laser, to produce 3D components. Other similar additive production processes, such as selective laser sintering (SLS) and Polyjet 3D resin printing, are also commonly used to produce the master pattern.
Once the master pattern is created to exact specifications, it is suspended in a box or frame with a gate assembly, and RTV silicone is poured around it so that the pattern is completely encased by silicone. The silicone is allowed to cure, and once completely cured, a few cuts are made to remove the master pattern from the mold. This leaves behind a silicone mold with a precise negative image of the master pattern. Urethane material is then poured into the silicone mold and allowed to harden. The hardened urethane casting is removed from the silicone mold and the RTV silicone molds can be reused again for casting additional urethane parts. Depending on the shore hardness of the silicone rubber used to produce the mold, 8 to 75 urethane castings can be produced from a single silicone mold tooling.
Colors as well as textures can be precisely replicated on the urethane part. While the former is facilitated by either adding the dye to the urethane material prior to pouring into the mold or painting the final part the latter is achieved by including the texturing in the master pattern. An advantage of using dye rather than painting the final urethane casting is that the colors do not get chipped off easily, as in painted components.
Post time: 02-27-2017