Reaction injection molding (RIM) has been used to create parts for a wide range of different industries—complex medical devices to construction equipment. As most product designers know, the manufacturing process you select will substantially influence the cost, aesthetics, and outcome of your final product. Thus, it’s essential to familiarize yourself with both the advantageous and adverse aspects of each manufacturing process in consideration. In doing so, you can best determine which process will best suit the specific needs of your project and when to use rejection injection versus other methods. Below, we highlight the notable advantages and disadvantages of reaction injection molding to help optimize your decision-making process.


Lower Molding Temperatures and Pressures

In comparison to other production processes, such as injection molding, RIM molding requires much lower temperatures and pressures. The ability to efficiently complete the molding process without using higher temperatures and pressures largely stems from the low viscosity liquids utilized in the RIM process. The combination of polyol and isocyanate creates a liquid with a consistency similar to that of motor oil, which allows the mixture to easily flow into every nook and cranny of even the most complex molds. Thus, no extreme temperatures or pressures are necessary to melt and form the plastic.


One major benefit associated with reaction injection molding is its low tooling costs. As stated above, the RIM process’ relatively low temperatures and pressures enable the process to employ tools made from aluminum rather than more durable materials, such as steel. Relative to steel tooling, an aluminum tool is more affordable to create and easier to modify. Thus, the tooling costs of reaction injection molding are generally much lower than those of other molding processes.


Another advantage of reaction injection molding is its ability to mold items into parts and still retain their functionality. The low pressures and temperatures involved in the RIM process can facilitate the encapsulation of a wide range of components, such as antennas, circuit boards, magnets, batteries, metal rods, and threaded inserts.

Encapsulation can be used for a range of products because it provides numerous benefits, such as enhanced protection for more fragile parts, theft prevention, and reduced parting lines. Thus, the option to encapsulate components into a part is highly desirable in a wide range of different applications.


Reaction injection molding is also ideal for producing larger parts. Since RIM tooling only requires low-cost aluminum, manufacturers have the capacity to create larger molds without paying exorbitantly large costs. The steel tooling needed to produce large parts using traditional plastic injection molding will usually cost several hundreds of thousands of dollars or more. RIM tooling costs would represent a small fraction of that amount. RIM is far more economical when it comes to producing larger parts—especially in smaller production volumes.


In addition to creating larger parts, RIM is also well-suited for designing and constructing parts with complex geometries like in the production of medical devices. Reaction injection molding differentiates itself through the high degree of design freedom it offers. For example, RIM can produce parts with differing wall thicknesses, curves, and encapsulated components, among other sought-after features.

Due to the low viscosity of RIM materials—which allows the materials to fill even the most detailed molds—and the lower tooling costs, which allow intricate molds to be created in an economical manner, RIM enables manufacturers to efficiently conceive and construct highly complex parts in a cost-effective manner. For this reason, RIM is frequently called upon to produce parts for medical devices and laboratory equipment.


The ability to reduce the number of parting lines on a part is another advantage supplied by the reaction injection molding process. As we previously stated, RIM allows manufacturers to encapsulate items directly into a part and produce larger, complex parts in an efficient and economical manner. In doing so, parts with fewer separate components can be created, which minimizes—and possibly eliminates—any unattractive seams or parting lines, which can weaken a part, collect dust, and detract from the part’s overall appearance.


Reaction injection molding also has a few disadvantages. As with any production process, there are certain applications for which reaction injection molding may not be appropriate. Its drawbacks are limited, but it’s important to recognize when reaction injection molding may not suit your specific project.

RIM generally isn’t well-matched for parts requiring larger production volumes. The ideal production volume range for reaction injection molding is between 100 and 5,000 parts per year. If your annual production volume falls within this range, the substantially lower tooling cost of RIM will greatly offset production expenses. However, since RIM also requires additional finishing and post-molding work, it generally has a slightly higher individual part price than injection molding.

Thus, when you need to produce parts in extremely high volumes, the higher individual part prices will inevitably surpass the cost savings provided by a less expensive tool. For this reason, RIM is a more advantageous production process for lower to medium production volumes than for extremely large quantities.


We hope this guide on the main advantages and disadvantages of reaction injection molding helps you determine whether RIM is an ideal method for your manufacturing project. If you think your project could benefit from the reaction injection molding process, Rimnetics can help. Rimnetics is North America’s premier reaction injection molding company for enclosures, cosmetics housing, structural parts, encapsulation, and over-molding. With over 30 years of industry experience, we have the skills and expertise necessary to make your unique project a success story at the lowest price possible—after all, we’ve done it thousands of times before. Learn more about the high-quality RIM services that Rimnetics provides; contact us today.

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