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Insert Molding

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insert molding

Extruded PEEK and Polycarbonate

insert injection molding

2 metal components and 2 polymers

PEEK insert molding

Part insert molded with PEEK

Insert molding is the process of molding or forming plastic parts around other non-plastic parts or inserts to create a single part. The inserted component is most commonly 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.

Insert molding is often compared to injection molding but the processes are significantly different. Injection molding involves injecting one or more molten plastic resin into a mold, when insert injection molding involves the joining molten resin onto a previously fabricated component.


What is the Insert Injection Moulding Process?

Insert molding (or “insert moulding”) is just one of the many specialized plastic injection molding services Stack Plastics offers. We utilize highly-advanced vertical molding machines that are specifically designed for insert injection molding. The insert molding process requires very tight tolerances to ensure correct formation of the plastic parts—misalignment of even a fraction of a millimeter can lead to complete failure of the process. Our state-of-the-art insert molding equipment can meet even the most exacting specifications.

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


Injection Molding Threads for Screw Thread Applications

Though it’s not technically insert molding, molding threads into plastic parts is a common production option that we provide. Internal or external threads can be molded directly into the part profile. Molding threads into your part makes 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, and American Standard machine screw threads (60° sharp threads).

There are a number of important factors to consider when designing threads for injection molded plastic parts, including thread profile width, thread radius, thread cross section, location, and spacing, among others. Whatever your design needs may be, we have the molding capabilities to create threads that meet your requirements.


Insert Injection Molding Solutions

Our insert moulding services are incredibly flexible and customizable, allowing us to create the ideal solution for your project's unique needs, no matter the requirements or application. We work with a variety of insert molding materials (see below) to give your project the exact properties it requires. From low volume prototypes to full production runs, Stack Plastics has the right experience and equipment to make your project a success.

Request a quote on insert molding, or contact us to learn how we can meet the needs of your project.


Insert Molding Materials

We use a variety of polymers in our insert 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 insert molding 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 moulding process include:

  • Nylon: a strong plastic material that is resistant to chemicals and abrasion. It is suitable for high temperature applications and can replace metal in certain applications.
  • Polyethylene: includes several different grades of lightweight thermoplastic polymer providing chemical resistance, high toughness, impermeability and excellent dielectric properties. Examples of polyethylene include LDPE, HDPE and MDPE plastics.
  • Polystyrene: a clear, lightweight plastic with a low melting point and resistance to acids and bases. It is a common insert molding material that is used for applications ranging from consumer products to medical devices.  



Thermoset insert molding materials are similar to thermoplastics, with the exception that they cannot be melted and reused after they are cured.

  • Epoxy: high performance polymers that become permanently hard after curing and provide excellent adhesion and heat and chemical resistance.
  • Phenolic: provides high chemical resistance to organic halogenated solvents, and many have UL 94V 0 approval.  



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.

  • Natural rubber: flexible and durable plastic commonly used in automotive applications.
  • Polyurethane: provides excellent wear and abrasion resistance and is highly elastic and impact resistant. This durable material maintains its properties in both high and low temperatures.

Our injection moulding machines and state-of-the-art equipment enable us to quickly adapt to the near-constant advancements our industry experiences. Advances in polymer technologies open up new avenues for our business each and every year. We welcome these advances, as we strive to provide our clients with the most current, cutting edge polymer technology.


Industries & Applications for Insert Molding

No matter the function of your injection molded products, whether it be rigorous outdoor use, applications in the consumer environment, or parts on vehicles that leave the earth's atmosphere, our quality has been tested in every possible environment and we proudly stand upon the back of 70 years of exceptional service.

We provide insert moulding services for clients in nearly every industry, including:


Contact Us for Insert Injection Molding & More

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