Understanding the overmolding and insert molding processes

by Walter Smith

When it comes to the world of high-precision engineering involving CNC machining processes, overmolding currently stands out as one of the most popular techniques. It can be applied for crafting complex components that match individual project needs. Also, overmolding and insert molding can be leveraged to insert plastic over other materials like metal, crafted circuit boards, and plastic. Applied correctly, both overmolding and insert molding has the innate potential to save costs and introduce novel design perspectives in the process of new component manufacturing. These techniques are heavily employed in crafting pens, hand tools, mobile phones, cars, commodities, and home appliances. Let’s focus on understanding the overmolding and insert molding procedures.

Understanding the overmolding and insert molding processes

As far as component design and manufacturing goes, overmolding involves complex techniques applied in plastic injection and contains different materials, including the substrate. In these chemical processes, a substrate is later completely covered using overmolding materials during the production process. In industry, substrates include plastic parts, screws, threaded inserts, and electrical connectors. Complete substrates are made of a range of materials joined by mechanical interlocking or chemical bonding.

The materials most commonly used in the overmolding processes include foaming agents, fillers, plastic (in pellet form), and colorants. However, a significant drawback of overmolding procedures is the limited materials available for overmolding, mainly plastic on plastic choices.

Since overmolding can combine two different plastic components into a single part, there is always a two-shot molding process to craft a finished plastic part. Finally, extra detailing work is done to design new styles and properties on the finished component.

The steps associated with overmolding and insert molding include mold clumping, connecting the nozzle, injection of melted plastic in a heating cylinder, cooling, mold opening to unclamp the mold unit, and ejection, where the molded parts are removed from the mold unit by the pin.

Types of overmolding

At its core, overmolding is creating a single component by leveraging technology to combine two or more different materials. Material number one is always the substrate, and the second material is the overmold.

  • 2K (also known as two-color) injection molding involves crafting different materials into finished products using a 2K injection molding machine. The 2K machine is also leveraged to conduct mold flipping and jumping to an additional note inside the mold cavities.
  • Two-shot molding involves taking the material part inside an injection molding machine and then inserting it into another mold, where a second material is injected into the mixture. In the manufacturing industry, insert molding is also known as wrapping or secondary injection molding.

Materials commonly used in overmolding

The most common materials used in the injection molding and overmolding processes include ABS (Acrylonitrile Butadiene Styrene), HDPE (High-density Polyethylene), PEEK (Polyether Ether Ketone), and PBTR (Polybutylene Terephthalate).

Others such as Silicone, Polypropylene, Thermoplastic Elastomers, Thermoplastic Rubber, Acrylic, and Polybutylene Terephthalate are regularly employed overmolding and insert molding.


It is normal to confuse overmolding with insert molding processes. Both can be rightly considered to be injection molding procedures that can be leveraged to craft similar parts. However, both are unique styles that offer different product outcomes.

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