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By Jeremy Losek, Aug 31st, 2023

Overmolding – Combining Two Plastic Materials Into One Part

Overmolding is a plastic injection molding process which is very useful for producing multi-material parts with some unique properties.

What is Overmolding?

OvermoldingOvermolding is the process of taking a part and then using plastic injection molding to add additional layers over the current part. With overmolding, you essentially take two different plastics and combine them into one part. Traditionally, it starts with injection molding a hard plastic resin that has a higher melting point. Then, once that part is cooled, another plastic resin is injection molded over the first part. Usually this is to create a grip or accents on the original part.

Typical Applications of Overmolding

To help clarify how overmolding is used in parts manufacturing, here are some examples of how the process is applied:

  • Over Plastic – It’s possible to overmold plastic onto plastic. First the primary, more rigid plastic component is molded and then the more durable plastic is molded over the previous plastic part.
  • Over Metal – Overmolding plastic onto metal is often used for making plastic handles on metal tools and components. It’s a similar process in which plastic is molded over the metal part.

What are the benefits of Overmolding?

Saves money and time

One of the biggest benefits of overmolding is saving money and time. Since it can be completed with two runs through our in-house injection molding process at ICOMold, it’s not necessary to outsource the overmolding as a secondary process at another facility. That means there is a cost and time savings by not having to schedule additional outside production.

Doesn’t require additional adhesive

This also can save quite a bit of money. By overmolding, the two pieces are bonded together without adhesive. Otherwise, you would have to setup an additional manufacturing run to attach the two pieces together with adhesive. You would also have to make sure the adhesive is compatible with the two materials, or else the parts will degrade and fall apart.

Different textures and design

With overmolding, you can combine two different types of plastic resins onto one part. This means you can have a rigid plastic body and then overmold soft silicone grips onto areas that an end user would grab, such as the handle of a tool. You also can overmold different plastic resins to have two very different textures and aesthetic design. For example, we overmolded a tire showroom display for a customer. The “rubber tread” material was molded over the harder, blue piece (substrate) that represents “water” in the tread. (Read this Overmolding Case Study ).

Are there special considerations for overmolding?

Overmolding is not without its limitations. One consideration is that the two materials must be compatible, chemically and thermally. Since the first piece is put back into a plastic injection mold, it is important that the first piece can withstand the temperature needed to melt the second material. Also, you will need to make sure the two resins don’t react to each other. That can cause the overmold to fall apart.  Finally, overmolding is not a straightforward injection molding process like making a part out of a single material. A high level of experience is required to successfully accomplish the process. This is a process we do well. In our many years of experience in plastic injection molding, we’ve successfully completed numerous overmolding projects for our customers.

Overmolding vs Insert Molding

On the surface, these two techniques look very similar. Overmolding takes a part and then overlays another layer of plastic injection molding material over it. One example would be taking a plastic handle and overmolding a soft silicone grip. Insert molding takes small parts and embeds them during the plastic injection molding process. For example, embedding brass wires in a plastic part to create a connector.

ICOMold provides dedicated project managers and engineers for your overmolding project. Use our instant online quote system when you’re ready to start your next project.

Overmolding — Injection Molding Highlights

  • Fast mold and part quote
  • Low cost, high quality and fast turnaround 
  • Mold frame sharing technology
  • Online project management
  • Trouble-free part modifications  
  • Any commercially available material and surface finish

Process for overmolding — Plastic Injection Molding

ICOMold’s online quoting system and mold frame sharing technology enables us to simplify and shorten both the quoting and tooling manufacturing process for plastic injection molding. 

  1. Load your 3D CAD file to get your mold and part quote.
  2. Add your requirements for overmolding in the comments, and your project manager will contact you.
  3. Upon order confirmation, ICOMold starts the mold and part order process.
  4. Tooling design review by ICOMold engineers.
  5. Upon design approval, ICOMold begins building your injection mold.
  6. Customer examines samples for approval.
  7. Part production begins.

Go to our plastic injection molding and CNC machining case studies page to see how we helped customers on their projects.

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Injection Molding for US Companies

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