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What Is the Overmolding Process?

When it comes to producing finished goods using injection molding processes, one option is called overmolding. This process results in a single finished workpiece being produced using a combination of molding steps where at least two types of plastic materials—or more—are molded together over each layer of material.

Overmolding can be used to produce a wide range of workpieces for numerous industries, including automotive, aerospace, medical, household goods, and so on. For instance, a plastic scrub brush with a soft plastic grip could be manufactured using overmolding processes.

Overmolding Injection Molding Process Steps

There are typically at least two overmolding injection molding process steps. Depending on the complexity of the finished workpiece being produced, there could be additional steps. However, the third, fourth, and subsequent steps would be similar to the second step.

Step 1: Mold the base layer of the workpiece.

The first step is to produce the base layer of the plastic workpiece. This is normally carried out through plastic injection molding, where a liquid plastic material is injected into a mold. Once cooled, the first-step material is placed into an overmolding machine.

Step 2: Apply the second layer to the workpiece.

This step is when the second layer of plastic material is applied over the initial base layer material. It can be a soft plastic or rubber and does not have to be the identical type of plastic material used for the base layer.

The multiple materials enhance the appearance or functionality of the finished workpiece. For example, a multi-colored toothbrush with a rubberized handle is one such product produced using overmolding processes.

How Is Overmolding Different from Multi-Shot Plastic Injection Molding?

While the processes can seem similar, there are some major differences between the two injection molding processes. With overmolding, the initial base layer is a single piece that is removed from the injection molding machine and placed into an overmolding injection machine.

With a multi-stage injection molding machine, a single workpiece is also produced, yet the materials are encapsulated over one another. There are multiple injectors and molds used in the process. The first plastic material is moved into a second mold where the second plastic material is injected and encapsulated over the first material.

Another key difference is that multi-stage injection molding is faster since a single machine is used to produce the desired workpieces. However, this method is not viable for every type of workpiece. Overmolding may be the better choice, depending on what finished goods you manufacture.

One of the primary benefits of overmolding is that it allows you to create work with a wide range of materials, applying a textured grip over a metal material. For instance, the plastic grips on pliers and other tools are normally produced using overmolding processes.


Another great example is a clamshell case made of hard plastic with a soft rubber casing on its exterior to absorb impact if it is accidentally dropped.

For further information about overmolding and injection molding processes and our customized overmolding and injection molding services, please feel free to contact Laszeray Technology, LLC at 440-582-8430 today! We also offer investment casting tooling, CNC production machining, secondary manufacturing, rapid prototyping, product design, engineering, finishing operations, value analysis, and value engineering services.

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