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AIM Processing Small Plastic Parts Blog

Plastic Overmolding vs. Conventional Injection Molding: Manufacturing Processes Compared

[fa icon="calendar"] Mar 22, 2024 1:33:00 AM / by Jon Gelston


Conventional injection molding and overmolding are both crucial processes in the realm of modern plastics manufacturing. The production processes are similar, but overmolding isn’t as simple as injecting one plastic material over top of another. It requires a specialized mold setup along with the unique procedure of placing the substrate (the initial injection molded part) precisely into an overmold cavity before injecting the second material.

Basically, overmolding allows you to place one type of plastic over top of another type so that you get the benefits of both materials. Commonly, that means using a rigid plastic base and generally a softer or more forgiving plastic on top to enhance the end product’s ergonomics, comfort, vibration dampening properties, etc. Better sealing, waterproofing, and sound deadening properties are other typical advantages customers are looking for in
overmolding services.

Below, we take a closer look at what sets the conventional injection molding process apart from overmolding.

Injection Molding vs. Overmolding: Comparing the Manufacturing Processes

Material Complexity – With conventional injection molding we’re only molding a single plastic material which simplifies the process. Overmolding involves molding multiple materials sequentially, which tends to complicate product design, the production process, as well as quality control. This may be accomplished in two separate molding operations in two separate manufacturing runs for lower volume applications. In very high volume production and at a larger upfront expense, there are injection mold and 2-shot machines that perform both manufacturing steps in one machine cycle.

Mold Design and Maintenance – Overmolding requires molds that are more complex which feature multiple cavities for the overmolded structures. The molds can feature multiple injection points to accommodate material flow into the different cavities. That means more complex tooling and setup with potentially more complicated maintenance requirements compared to standard injection molds. In essence, overmolding often requires a doubling in upfront tool cost to support the two future production processes to make your product.

Part and Material Complexity – Overmolding allows for the creation of more complex parts with multiple materials and uniquely engineered physical/mechanical properties. However, materials must be chosen carefully to ensure compatibility. With conventional injection molding material choice is crucial as well, but you’re only dealing with a single type of plastic. That simplifies the engineering and production processes but limits your end product options.

Cost and Time – Due to the above details, overmolding will typically be more expensive and time-consuming than conventional injection molded parts due to the complexity of mold design and the need for additional processing steps.

When should you choose plastic overmolding services?

If you’re manufacturing plastic devices for end users that demand enhanced user comfort and ergonomics, our overmolding services are often the best option. We apply our expertise in materials science to your unique product designs to achieve the exact physical and mechanical properties you’re looking for.

Alternatively, many products come with special requirements such as the need for waterproof mating surfaces, other sealing requirements, vibration dampening, sound deadening, etc. Overmolding allows us to take advantage of multiple materials to achieve these unique requirements and ultimately build a more premium product.

When should you choose injection molding services?

If you’re manufacturing simpler plastic parts, or your products have no special ergonomic/comfort requirements, conventional injection molding is the faster, simpler, and more cost-effective solution. With injection molding we can still produce extremely complex parts with uniquely customized features – we simply can’t combine multiple materials like we can with overmolding.

Complete Injection Molding Services and Overmolding Solutions

As one of the Colorado area’s premier injection molding companies since 1993, AIM Processing specializes in custom overmolding services for a wide range of unique plastic products. Our company is an ISO 9001:2015 registered American manufacturer dedicated to superior quality end products.


Topics: Plastic Injection Molding Defects, Plastic Types, Quality, Texture, Choosing the right plastic injection molder

Jon Gelston

Written by Jon Gelston