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Before you start manufacturing products, you should know exactly what will come out of the workshop machines and how to finish and assemble them to get the expected result. This is where prototypes enter the picture.

By producing a prototype, you actually produce a copy of your intended product. There are prototype manufacturers who specialize in materials such as metal, and then there are companies that can work with exciting new technology such as 3D printers to produce cheaper prototypes for any industry.

One of the ways to create prototypes is by using the overmolding manufacturing process. With overmolding prototypes, you can test the ability and durability of the material and the ease of use.

Below, we’ll discuss overmolding prototypes so that you can gain a better understanding of the overall process.

What Is Overmolding?

Overmolding can be described as a process where a single part is formed with two or more different materials in combination. Usually, the first material sometimes referred to as the substrate, is completely or partially covered by subsequent material (overmold material) in the course of the overmold manufacturing process.

This process enables us to, for example, use more than one layer of rubber or plastic to make industrial parts much stronger, more aesthetic, or more functional.

The Role of the Substrate


The substrate can be anything from a machined metal part, a molded plastic part, or even an existing product such as screws, threaded inserts, or electrical connectors. It’s the first piece that will ultimately turn into a single continuous part composed of chemically bonded and mechanically interlocked materials of separate types.

Overmolding Materials

Overmold materials, which typically come in plastic, start in pellet form . These pellets tend to be mixed with additives such as foaming agents, colorants, and other types of fillers. They’re heated to their melting point and then as a liquid, they’re then injected into the mold. There are certain limitations as to what materials are suitable for overmolding.

If you’re planning to overmold a metal part with plastic, you can use any plastic, but if you are to overmold a plastic part with another plastic, rubber, or TPE , then there might be compatibility issues. In such cases, the material manufacturer usually publishes a compatibility chart for overmolding.

What Is Overmolding Used For?

Depending on the specifics of a particular project, the overmolding process is used for different reasons. Common materials include tool handgrips like screwdrivers, toothbrushes, and personal care products like shampoo bottles.

Some examples of typical overmolding applications include:

  • Plastic over plastic. At first, a rigid plastic substrate is molded followed by another rigid plastic which is molded onto or around the substrate. The plastic can be different in color or resin.
  • Rubber over plastic. A rigid plastic substrate is first molded then a soft rubber or TPE is molded onto or around the substrate to give a soft grip area to a rigid part.
  • Plastic over metal. A metal substrate is machined, cast, or formed first and then the substrate is inserted into an injection molding tool and the plastic is molded onto or around the metal aiming to capture metal components in a plastic part.
  • Rubber over metal. A metal substrate is machined, cast, or formed and then the substrate is inserted into the injection molding tool and the rubber or TPE is molded onto or around the metal to provide a soft grip surface.

When using different materials, there are certain limitations and compatibility issues you need to consider. You’re not limited to two materials only as there are also products that contain three different materials on one part aiming to achieve grip surfaces and color breaks.

How Is the Process of Overmolding Achieved?

The substrate materials or part is typically placed into an injection molding tool at which point the overmold material is shot into, onto, or around the substrate. The two materials join as a single part once the overmold material cures or solidifies. It’s recommended to have the substrate and overmold material interlock in some mechanical capacity as this way, not only will they be bonded chemically but also help together physically.

Final Thoughts

The most common reason for using overmolding is to manufacture parts , sub-section of parts, and develop prototypes. Overmolding provides a soft grip surface around a part of a separate material, breaks up colors, and adds flexible areas to a rigid part. If you’re considering developing prototypes, make sure to know how overmolding works and what to look for in materials.

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