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Reaction Injection Molding Vs. Plastic Injection Molding: What’s the Difference?

injection molded enclosure

Injection molding processes are typically used when a business requires large quantities of plastic parts. But it’s not always easy to know what kind of injection molding process will work best for your needs. Often, the type of injection molded enclosure you want as your final result, as well as your budget, can allow you to make the correct determination. If you’re currently trying to decide between two popular types of injection molding — namely, plastic injection molding (PIM) and reaction injection molding (RIM) — this post may help you to gain a better understanding of the differences between these two methods. With that knowledge, you’ll be in a better position to decide which technique will more accurately serve your business’s needs.


Main Differences Between Reaction Injection Molding and Plastic Injection Molding

    • Materials Used: Although both techniques do involve the application of heat to a plastic component, each one utilizes slightly different substances to achieve the desired effect. Plastic reaction molding requires the use of some type of resin. Often, this resin is in pellet form. This resin is melted down and dispensed into molds using pressure. Once that heated resin cools, it sets into its final form. Reaction injection molding materials, however, are actually two different base polymers that are combined. When these thermoset materials come together, they undergo a chemical reaction that will force the combined polymers into the molds. Once those two materials come together, the mold containing the polymers are heated. In this case, it’s the heating that causes the materials to set, rather than the cooling we see in PIM applications.


    • Design Flexibility: In general, plastic injection molding requires more rigidity throughout the process. In other words, the injection molded enclosures produced from this technique must be less variable. Wall thicknesses must be relatively uniform and designs must be uncomplicated. Although recommended wall thickness for RIM molded parts for solid materials is typically 1/8 inch, wall thickness can retain its quality at 1/2 inch, as well. What’s more, the wall thickness throughout reaction injection molded enclosures can change without disrupting the quality of accuracy of the final product. RIM can also create parts that are both lightweight and durable, which can often be a challenge when using PIM techniques. Finally, decoration methods can be performed during the molding process itself with reaction injection molding; with plastic injection molding and other techniques, decoration must often be performed afterwards, adding delays, costs, and frustrations for many businesses.


  • Costs: Many businesses find that the cost differences between RIM and PIM are fairly significant, as well. Because RIM doesn’t require the application of extremely high temperatures, the materials required for reaction injection molds can be softer (and therefore of lower cost). Because tooling costs are lower, that may even mean that businesses will be able to have low-volume production runs and make prototyping a more realistic goal. In general, RIM is a less intensive process that requires less labor and lower machining costs. In PIM, equipment and machines must be made to withstand more extreme conditions, which drives costs up. Subsequently, RIM may be the most cost-effective option that can easily work into a business’s budgetary constraints during production.

In many cases, businesses will find that reaction injection molded enclosures can provide the durability, flexibility, and affordability they require — especially when compared to other popular options.

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