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MPC Polyurethane Knowledge Center

Insert Molding with Polyurethane

Insert molding is a key design technique to improve fit and function of your product or component. While there are several manufacturing processes available to include inserts in molded products, identifying the right process is key to delivering the product's required performance. In this post, we discuss the benefits of insert molding and the types of materials available for unlimited design freedom without sacrificing performance. Insert Molding with Polyurethane

What is Insert Molding?

Insert molding is a skilled manufacturing technique where a material in liquid form is layered over one or more subcomponents to produce a particular product. This technique is often specified in various applications that require improved functional and/or mechanical properties. For example, encapsulated inserts can often provide an unbreakable bond when compared to secondary assembly operations. To learn more about the advantages of bonding subcomponents to molded parts, click here. While inserts come in various materials including metals, plastics, silicone, and rubber – It is important to consider your manufacturing process and design requirements to achieve optimal results. 

How are Inserts Molded into Parts

There are three ways to encapsulate inserts during the molding process. For starters, a chemical bond can naturally develop with materials that feature a compatible chemistry and manufacturing process. This often includes a wide range of plastics such as thermosets with thermosets or thermosets with certain thermoplastics. Materials that do not feature a compatible connection, such as injection molded ABS or Elastomeric RIM, will require adhesives to ensure a proper bond. For products that prefer an alternative method, a mechanical interlock can be utilized for its unique design features, such as undercuts, thru-holes, and knurling. Because of this, a natural grip can take place during the curing process without the use of adhesives. While all three methods are effective separately, in combination they can offer superior torque and bond strength. 

When to use Inserts in Your Product Design

Insert molding is a common technique utilized in various applications from food processing, military & defense to medical devices – you name it! Because of this, there are different types of inserts available in various shapes, sizes, and forms to meet exact design needs. Some common examples of inserts can include shafts, bushings, sleeves, hubs, and filters. While molded inserts commonly act as connectors to other components, certain inserts can also reduce part weight & size and/or Insert Molding with Polyurethane increase part stiffness. For this reason, applications such as robotics often benefit from molded inserts to extend wear life. Due to the size and complexity of most robotic housing systems, durability, lightweight, and tight-fit tolerances are often specified during the beginning development stages. At MPC, insert molding can be accomplished through either a cast or Reaction Injection Molding (RIM) process to meet exact design needs without sacrificing performance. Designing with thermoset polyurethanes, in particular, offer a more controlled temperature and pressure system to mold virtually anything. To learn if cast or RIM is right for your product design over injection molding, click here


Insert molding has many benefits to improve your product's overall functional and/or mechanical properties. While there are three methods to encapsulate various forms of inserts in your product design, it is critical to select the right manufacturing process for optimal performance. If you are considering inserts for your product design, complete our design tool, here, to bring your vision to life! 

MPC Design Tool

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