Reaction Injection Molding (RIM) is widely used in the low volume prototyping or manufacturing of automotive bumper and large body panel parts for its economical cost and fast lead time, however the costly raw material and long molding time of RIM part result in not all the low volume manufacturing projects are suitable for this process when the production quantity over a certain amount. So what is the proper quantity for our reaction injection molding process? It needs to be comprehensively considered from the below points.
The RIM tooling materials we applied are normally epoxy resin and silicone rubber, the tooling fabrication method is similar to silicone rubber mold for polyurethane casting, thus the RIM tooling cost is only a fraction of its related rigid ferrous mold, usually 1/10 or ever less. Furthermore, it usually takes about 10 days for RIM tooling making, while its rigid ferrous mold needs 60 days or more time. Therefore RIM tooling has the great cost and time advantages compared to the conventional rigid ferrous mold for high volume production.
The RIM part material is the costly bi-component polyurethane that has much lower viscosity than the regularly used engineering materials with price around 2.5USD per kilogram, while RIM part material costs around $14USD per kilogram, which means 5.6 times higher. In addition to the material cost, the lead time of one RIM part usually takes 3-4 hours, while its mass production part made by injection molding takes just 2-3 minutes. So RIM part takes much more money and time.
In addition, the surface quality of RIM part is not as good as the injection molded part that could directly deliver the desired surface finishing without the time-consuming post processing such as the sanding and painting that are usually done for the RIM parts. Therefore the high surface finishing quality requirement will considerably raise the RIM part cost and its production time, especially with the increasingly high labor cost.
All in all, reaction injection molding process has the great advantage of low tooling cost and the disadvantage of costly part, so when the RIM tooling cost advantage is offset by its RIM parts cost since the production quantity over the certain amount, the reaction injection molding is no longer the competitive process. Taking our years of RIM low volume manufacturing experience in practice, the proper production quantity for RIM process ranges from 10 to 100 units, and it could be reconsidered when the low volume production quantity over 100 units.