RIM, Injection Molding, and Encapsulation?
RIM stands for Reaction Injection Molding. Though it is a somewhat similar process to injection molding, there are some key differences in both technique and the finished product.
Low-viscosity liquid polymers are used in RIM Molding. This ensures that lightweight and cost effective polymers are always used. Liquid isocyanate and polyol are the two liquids or reaction injection molding materials, that begin the process and are stored in large tanks. As large high-pressure pumps stir the liquids in a continuous loop, a piston retracts inside the mix-head to break the loop and combine the liquids.
A high velocity of 1200 psi is used to combine the liquids before transferring the liquid combination into a mold to cure. Lightweight aluminum molds are used for RIM because of the lower temperatures needed to complete the process.
The polymer mixture then cures inside the mold at a relatively low pressure of 100 psi and heating to 82 degrees Celsius. The cure time may vary by several minutes depending on the project being molded. Factors such as thickness, size, and complexity will all affect the cure time. For molds, containers and the packeging category has the most tonnage of plastic at over 14 million tons.
In comparison, encapsulation (also known as insert molding or multi-material molding) allows smaller encapsulations to be placed into a mold the traditional way. However, there are some varieties of encapsulation such as multi-component injection molding, multi-shot injection molding, and overmolding. Overmolding can be performed using standard RIM equipment, while the other two require special tools. Be sure to understand what type of encapsulation your project requires so that you have the right tools on hand to perform the mold. If you are overmolding for your encapsulation, RIM tools can be used, as RIM has many advantages as a type of molding.
Advantages of RIM
Cost Effectiveness: RIM is traditionally more cost effective when compared to encapsulation or injection molding. This is especially true with lower volume molds.
Tooling Cost: Traditional injection molding is usually much more expensive to tool than RIM. RIM can save you not just in cost effectiveness of lower volume molds, but also in cost of tooling.
Labor Requirements: The labor requirements for RIM are much lower than encapsulation or injection molding, again, saving you time and money.
Energy Efficient: RIM is much more energy efficient that injection molding or encapsulation, which is good for your wallet and the environment.
Space Saving: RIM requires much less floor space than injection molding.
There are many other advantages to the final product from RIM, such as variable wall thickness, strong and flexible parts, lightweight molds which can easily be painted, etc. There are also very fast cycle times, which allow for more molds to be cast. Additionally, a RIM mold will process foam that has a high density skin and a low density core. One of the only disadvantages to RIM is that it has more expensive raw materials, however this is usually offset by the savings in every other part of the process as well as the higher quality molds produced.