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Plastic Injection Molding: Overmolding
Apr 10, 2020

Plastic Injection Molding: Overmolding


The overmolding process is to make a new part using a combination of two or three or even more kinds of plastic or elastomer materials. During the plastic overmolding process, usually hard material is first-shot, and then soft material will be the second shot over the first layer molded part.

What is Overmolding?


Overmolding is used for a range of applications including medical, automotive, daily products, sanitary products and more. The purpose of overmolding is to increase the user comfortability, so usually the second shot material will be SEBS or so. Benefits of plastic overmolding include:

  • Improve grip and ergonomics
  • Provide electrical insulation
  • Create a waterproof seal
  • Dampen vibrations or absorb sound

Plastic overmolding can help reduce production time because the second piece is molded directly onto the original part rather than having to completely manufacture the two pieces separately and then assemble them.  Over molding is also a very difficult process, requiring adherence to the very tightest of tolerances.

The Difference Between Overmolding vs. Insert Molding


The general concept of overmolding vs. insert molding is quite similar but there are distinct differences between the two processes. Overmolding is a two-step process where two separated molds are required to produce the final molded parts. They are permanently joined together but the process does not involve full encapsulation.

The process for insert molding is different because it just needs a single plastic injection mold.  Insert molding is a slightly faster process because the second part (usually it is metal part, nut or pin) will be put directly into the mold to form final injection molded part. During this process, the melted plastic resin is injected into a mold and a plastic piece is inserted into the mold to produce an encapsulated finished product.


Qiqiangsheng Moulds' plastic overmolding processes create parts specifications as tight as 0.001”. We utilize the most advanced injection molding equipment for overmolding to ensure the highest possible quality and superb repeatability. Different types of overmolding injection molding we provide include:

  • Plastic over metal
  • Rubber over metal
  • Plastic over plastic
  • Rubber over plastic

What Material Combinations Can You Use for Overmolding?


Overmolding is often used to create a textured or comfort grip surface on metal components so an initial part of the material selection process is reviewing different material properties to see which will produce the desired results. This become a bit trickier when using more than one material because material properties can change when two or more resins are combined.


Compatibility is key for the overmolding process, so there may be some limitations as to which overmolding material combinations you can use. There are also important considerations regarding thickness effects, hardness, and coefficient or friction to ensure compatibility between your overmolding materials.


Specialized Plastic Overmolding to Meet Your Design Requirements


Qiqiangsheng Moulds has the expertise to make sure your overmolding project is a success. We provide guidance throughout every step of the process from design to final fabrication and assist with troubleshooting if issues arise.

Since the materials we use shrink as they cool following the overmolding process, special considerations are made during the mold design process to accommodate for changes in dimensional tolerance. Our mold designers will perfectly match their mold specs to the unique needs of your overmolding project. And because we use several different materials in overmolding with different cooling/shrinking properties, we create our molds to match the specific properties of the material(s) being used.


The variety of materials we use, the precise capabilities of our equipment, and our mold design services make our overmolding process extremely customizable. Qiqiangsheng Moulds will work with you to create the ideal solution for your exact needs. No matter what the specifications of your project, no matter how low- or high-volume your production run will be, Qiqiangsheng Moulds will meet or exceed the expectations of your next overmolding project.

Contact Qiqiangsheng Moulds for Injection Overmolding


Contact Qiqiangsheng Moulds to discuss material selection and tooling requirements for your overmolding project.

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