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MPC Polyurethane Knowledge Center

Cast Molding vs Reaction Injection Molding

Cast molding and Reaction Injection Molding (RIM) are manufacturing processes that are commonly used with thermoset polyurethanes. So, what differentiates these two, you may ask? In this post, we will uncover both methods and their differences. 


What is Cast Molding?

Cast molding can introduce liquid materials into open and closed molds to set and cure.  This flexible process can be as simple as hand pouring materials into a mold or as complex as a fully automated process. Unlike other methods, cast molding can offer a significant amount of customization to meet specific design and performance requirements. Due to their unique chemical structure, thermoset polyurethanes can be engineered into a solid or foam and portray a wide range of physical properties and surface finishes. Because of this, several molding techniques can be utilized, such as open molds, close molds, and centrifugal molds to name a few. To learn more about the tooling options for thermoset polyurethanes, click here. In general, cast molding can be a great solution to develop rapid prototypes for validation to small and large volumes.

What is Reaction Injection Molding?

Reaction Injection Molding (RIM) combines the superior properties of thermoset polyurethanes with the adaptability of injection molding techniques. RIM introduces thermoset materials into a closed, metal mold under heat and pressure, allowing for a chemical reaction to occur. Despite employing similar chemistries as cast molding, RIM offers a more limited material set, such as elastomeric, structural, and rigid foams. This controlled process is often ideal for manufacturing large, intricate geometries that may be otherwise difficult to achieve from a casting process. For this reason, RIM is generally best used for structural parts, enclosures, and housings that can be found in medical, robotic, and fitness & recreation applications to name a few.

Benefits of Cast Molding & Reaction Injection Molding

Cast Molding Reaction Injection Molding
  • Customizable options are available to meet specific design & performance requirements
  • While material options are limited, RIM can produce elastomeric, rigid, & structural foam products
  • Various manufacturing techniques can be employed to meet small & large volumes 
  • This controlled process can accommodate highly detailed parts in small & large volumes 
  • Can produce both small and large products & components 
  • Ideal for large geometries that feature variable wall thicknesses
  • Products can feature encapsulated inserts, molded surface finishes, and in-mold color
  • Products can feature encapsulated inserts and meet specific aesthetic requirements 

Which process is best for you?

While both processes employ the superior properties of thermoset polyurethanes, cast and RIM have their own unique advantages. For instance, cast molding can employ a very wide range of custom formulations while RIM offers the ability to manufacture products with more complex geometries. When evaluating a manufacturing method, it is critical to consider the design requirements, volume, and tools needed to achieve efficient products.

If you believe cast or RIM may be the right manufacturing process for your product design, complete our design tool, here, or download our material data sheets below to begin your custom product or component!

Download Our Durethane Material Data Sheet

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