Benefits of Overmolding and Insert Molding

Injection molding is the most widely used plastic manufacturing process in the world, but it has some limitations. The biggest limitation to injection molding is that it is best for simple plastic parts that need to be made in huge quantities. So what do you do if you need complex, multi-material molded parts?

That’s where overmolding and insert molding come in. The two processes are similar, and both allow you to create a single part using a combination of two or more plastic or elastomer materials.

What Is Overmolding?

Overmolding involves molding a base layer first, then molding additional layers over or around the original part. One of the most common examples of overmolding is a toothbrush with a stiff frame and rubberized grips on the handle. You can also use overmolding to create flexible areas on rigid components or add color contrast for aesthetics.

Overmolding Vs Insert Molding

While overmolding is a two-step process where separately molded plastic parts are combined, insert molding can start with any substrate, including metal, and involves encapsulating a product in molded plastic.

What Materials Can You Use for Overmolding?

Material properties can change when two or more resins are combined, so it’s important to choose compatible materials to get the results you want. Some common materials used for injection overmolding include:

PEEK, a high-performance plastic that is FDA-approved and suitable for use in medical device applications. It has high temperature and chemical resistance and resists fatigue and stress cracks.
ABS has good dielectric properties, high toughness and impact strength, excellent ductility, and the ability to be alloyed with other polymers. It provides good resistance to oils, acids, heat, and alkalis.
Acrylic Thermoplastics are scratch-resistant, have high tensile strength, are resistant to UV fading, and provide excellent weatherability. They are available in FDA-approved grades for use in medical and food applications.

Overmolding Examples

Here are some common examples of overmolding and insert molding:

Rigid plastic over rigid plastic
Rubber over rigid plastic
Rigid plastic over metal
Rubber over metal