Two important considerations when evaluating overmolding are volumes and speed. The upfront tooling investment for overmolding is higher than insert molding primarily because you are, in essence, making two parts; a substrate and the overmold. Forum’s tool financing can help address this upfront investment.

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When designing a product, it can be challenging to determine the best solution to fit the application. This holds true when considering overmolding and insert molding. While the general concept of these terms are similar, there are differences between the two processes. Their application – and what you are looking to achieve – needs to be considered when deciding the right fit for your application.

Form Plastics has extensive experience with insert molding, and we have worked with various materials including stainless steel pins and tubes. Forum has the ability and expertise to also overmold brass and bronze bushings. Our engineering team can work with you to determine feasibility and make recommendations on the best process and tool design.

Forum provides design for manufacturing support and will proactively make cost avoidance recommendations for any necessary changes to the insert to aid in overmolding or insert molding. Contact Doug Hungerford, Director of Engineering, to learn more about our capabilities and how we can support your product development.

This process is faster because it is happening in parallel or at the same time – in comparison, overmolding can require two or even three shots. Some examples of this can be a gear onto a metal shaft, metal guide pins into a plastic part, or metal hooks that may need a plastic retainer.

When working with product designers, the considerations that need to be accounted for when choosing a substrate and TPE are:

Overmolding is typically plastic-over-plastic or a rubber-type resin over a plastic substrate providing a grip surface. Overmolding a plastic gear or cams onto a shaft are the most common application. Some examples of applications include small cams used in infusion pumps, plastic gears on bushings for ATM machines, mail processing, or in vending machines.

Insert molding differs from overmolding because rather than joining two different materials, it involves encapsulating a product in molded plastic. Insert molding usually involves placing a metal insert, part or pin into the mold and overmolding plastic onto it. The process involves injecting melted plastic resin into a mold and then a plastic or metal component is inserted into the mold to create the encapsulated finished part.

Overmolding is typically used when a product designer is trying to create a single part using a combination of two or more different thermoplastics. It involves multiple “shots” to create the one part. The “first shot,” also known as the substrate, is typically the more rigid of the two materials being combined. This mechanical bond creates a part that has both strength and durability.

A wide variety of thermoplastics can be used for the “second shot,” or overmolding, of the substrate. These materials are typically more flexible or softer, and various additives can be used including foaming agents, colorants or other materials to achieve a desired texture, aesthetic or feel. These are used to address ergonomics, sound absorption, dampening of vibration, improved grip surface, the need for a water-type seal, or even electrical insulation.

Insert molding typically requires a unique mold design to load, capture and verify that the insert is properly in-place. Forum has made the necessary equipment investments and typically uses our vertical shuttle press for insert molding, but a conventional molding machine can also be used.