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What Is Overmolding in Injection Molding?

Over molding in Injection Molding

Injection molding is the process of injecting melted plastic into a mold to produce high-quality, precision parts. It’s widely used in a variety of applications, including automotive components (e.g., seats, structural reinforcements), consumer goods (grips and handles, pot covers, electronics components), and medical devices.

In injection overmolding, a rigid substrate part is formed in a separate step before a second shot of a more pliable material is injected over it to form the final product. The bond that holds the two layers together can be chemical or mechanical, depending on the materials and the part’s design.

The first step in any overmolding project is evaluating the substrate and overmolded material to make sure they are compatible with one another. This includes examining the materials’ tensile properties, as well as their heat resistance and flow. The temperature of the overmolded layer can have a significant impact on how it adheres to the substrate, and how easily it can be separated from it.

Overmolding also requires careful consideration of the part’s overall geometry and features, such as draft angles, ribs, embossed text, and hole locations. Any complex geometries can be a challenge for the what is injection molding process, and it’s important that they’re designed with manufacturability in mind. This ensures that the finished part meets its functional requirements and can be produced in a way that minimizes production costs.

What Is Over molding in Injection Molding?

The substrate and overmolded materials may need some pre-processing prior to injection, such as surface treatment or heating. This can help improve the adhesion between the different materials. If the overmolded material is very soft, it can also be conditioned with lubricant to reduce friction between it and the substrate.

Whether the bond between the overmolded material and the substrate is chemical or mechanical, it’s essential that it be strong enough to hold up to the stresses of daily use. This means selecting a tough, durable material that can resist damage from UV light and harsh chemicals.

For mechanical bonds, it’s also helpful to consider how the two materials will interact. If the overmolded material will be in contact with a hard, sharp edge of the substrate, for example, it’s important that the material be able to withstand indentation without peeling.

Injection overmolding is often done for aesthetic reasons, to create more comfortable or secure grips on a part, to dampen vibration, or to provide a water-resistant seal. But it can also be used for more practical purposes, such as creating a more comfortable grip for a handle or providing better protection for delicate electronic components. Choosing the right combination of materials can have other benefits as well, such as increasing the durability of a part or improving its performance in specific environments or applications.

With over a decade of experience in metal processing and plastic processing, Firstmold has honed its expertise to perfection. Our team of more than 200 professionals brings a wealth of knowledge to every project, ensuring exceptional quality and precision in every aspect of our work. From design and R&D to production and assembly, Firstmold’s integrated approach guarantees seamless coordination and superior results.


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