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MPC Polyurethane Knowledge Center

Reaction Injection Molding vs Compression Molding

Reaction Injection Molding (RIM) and compression molding are two distinct manufacturing processes that offer different advantages for producing parts made from thermoset materials. In this post, we will explore the differences between these two methods and highlight their unique advantages.


What is Reaction Injection Molding (RIM)?

RIM partRIM is a process that combines the superior properties of thermoset polyurethanes with the adaptability of injection molding techniques. During the RIM process, thermoset polyurethanes are introduced into a closed, metal mold under high heat and high pressure, allowing for a chemical reaction to occur. RIM is typically ideal for manufacturing large, intricate geometries that may be otherwise difficult to achieve from a cast molding process. Moreover, RIM is well-suited for producing structural parts, enclosures, and housings that can be found in various applications such as medical devices, robotics, and fitness & recreation. To learn more about the types of products achievable through a RIM process, click here

What is Compression Molding?

Compression Molded PartCompression molding is one of many techniques related to cast molding However, high compressive forces are used to achieve the desired net shape. Unlike RIM, a specific amount of liquid is placed into the center of an open mold cavity. Before the mixture begins to solidify, a second mold is placed on top to compress the same shape and surface of the mold cavity. While various materials can be used, such as thermoplastics, compression molding with thermosets like polyurethanes provides a good solution to obtain a wide range of shapes, sizes, and forms. 


Benefits of Reaction Injection Molding vs Compression Molding 

RIM and compression molding offers a unique set of benefits for various applications. Here is a list of some of those key benefits to consider in your material selection: 

Reaction Injection Molding Compression Molding
  • Can offer a broad range of materials and customization to achieve specific performance requirements 
  • This controlled process can accommodate highly detailed parts in small & large volumes 
  • Several techniques can be utilized to achieve complex geometries & fine features without secondary operations
  • Can produce both small and large products & components 
  • Products can feature encapsulated inserts and specific aesthetic requirements
  • Products can feature encapsulated inserts, molded surface finishes, & in-mold color
  • Commonly used to produce structural parts, enclosures, and housings
  • Commonly used for seals & gaskets, electronic components, and automotive parts

Which Manufacturing Process is Best for You?

As mentioned above, Both RIM and compression molding have their unique set of advantages. Selecting a manufacturing process will depend on the design and performance requirements of your final product. For example, if the product requires large, complex geometries with varying wall thickness, RIM might be a better choice. On the other hand, if the product requires specific physical properties and intricate details, compression molding might be a better option. 

Ultimately, the best manufacturing method will be the one that meets the specific needs of the product and provides the required quality and performance. If you believe RIM or compression molding may be the right manufacturing process for your product design, complete our design tool, here, or download our material data sheets below to get started!

Download Our Durethane Material Data Sheet

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