Insert Molding

Insert Molding

Insert injection molding involves encapsulating a previously fabricated component in molten resin to produce a finished part. The inserted component is usually a simple object, such as a knife blade or surgical tube, but in some cases, inserts can be as complex as a battery or motor. 

Plastic insert molding is ideal for improving the strength and reliability of a component and can help save on cost and production time by eliminating the need for secondary operations such as soldering, connectors, and adhesives.

Insert Molding vs. Overmolding vs. Injection molding

Overmolding is a two-step process where a plastic layer is molded over and around a previously molded part to produce a single component. Similar to this, insert molding involves joining separate parts to form a single component, but the difference is that the insert molding process is only a single step. The preformed insert and molten resin are placed in a mold together to combine two parts.

Insert injection molding is similar to other molding methods, but there are some differences between each of the processes. Injection molding involves injecting one or more molten plastic resins into a mold to create a single finished part.

Insert Injection Molding Inserts 

This type of molding is typically made from brass, steel or stainless steel and have a threaded surface to provide better adhesion to the plastic. Injection molding inserts are placed in the mold either by hand or by machine with the mold in a vertical position.

This positioning allows gravity to keep the insert in place as the mold is closed. As the molten plastic resin is slowly poured into mold, it helps hold the insert in a fixed position. 

Plastic Insert Molding Process 

Insert molding (or “insert molding”) is just one of the many specialized plastic injection molding services Springboard offers. Using highly-advanced vertical molding machines, our process achieves tight tolerances to ensure correct formation of the plastic parts. 

To guarantee that the metal insert parts match your specifications, we’ve forged sound working relationships with numerous vendors who supply us with high-quality metal insert components. We will also work with customer-supplied inserts, as your project requires. 

Other benefits of the process include:

  • Flexible and customizable to meet your needs
  • Available in a variety of materials
  • Ideal for low volume prototypes or full production runs

Injection Molding Threads for Screw Thread Applications 

Though it’s not technically insert molding, we also provide molding threads into plastic parts. Internal or external threads can be molded directly into the part profile, making it easy to attach other components via screw threads. 

Threads in all sizes and types (fine, coarse, etc.) can be injection molded. Some of the most commonly specified threads for molded plastic components include: 

  • Tapered pipe threads
  • Buttress threads
  • American Standard machine screw threads (60° sharp threads).
  • Medical luer  (including the new standard, ISO 80369) 

There are several important factors to consider when designing threads for injection molded plastic parts, including: 

  • thread profile width
  • thread radius
  • thread cross section
  • location
  • spacing

Whatever your design needs may be, we have the molding capabilities to create threads that meet your requirements.

Plastic Molding Materials

We use a variety of polymers with our molding processes to meet your application requirements. Each material contains unique properties and should be selected based on the operating conditions and performance requirements of your finished component.


Thermoplastics are an environmentally- friendly  material that can be reheated and reused. They are often chemical resistant and provide various options for sheen, variance, and other properties. A few of the thermoplastic materials we offer for the insert molding process include nylon, polyethylene, and polystyrene. 


Thermoset molding materials are similar to thermoplastics, with the exception that they cannot be melted and reused after they are cured. Common thermoset materials for molding include epoxy and phenolic.  (note that Thermoset materials cannot be processed in our Injection molding shop)


Elastomers include natural and synthetic polymers such as rubber that are known for their elastic properties. Elastomers are recyclable and commonly used for home and automotive applications. Common elastomers used in this molding process include natural rubber and polyurethane.

Insert Molding Uses

No matter the function of your injection molded products, our quality has been tested in every possible environment and we proudly stand upon the back of 70 years of exceptional service. We provide plastic molding services for clients in nearly every industry, including:

Contact Us for Custom Plastic Insert Molding Services

We have the insert molding experience and expertise to deliver the complex parts your project requires. Request a quote today or contact Springboard for full-service injection molding for your unique application.

Phone: 916-853-0717
Fax: 916-853-0711

2691 Mercantile Drive, Rancho Cordova, CA 95742
404 West 8th Street, Kearney, NE 68845
3525 Haven Ave, Menlo Park, CA 94025



Plastic Injection Molding

In-Process QC and Product Testing

Multi-Component Product Assembly

Special Packaging




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