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Best practice: Overmolding of plastic and metal parts

How you can harness the power of two-component injection molding to improve your products

If you’re looking for a way to improve the functionality and aesthetics of your products, consider overmolding. Overmolding is a manufacturing technique that combines two different materials using injection molding to create unique and high-quality products. In this best practice post, we will explain what overmolding is, the benefits it offers and the best practices you should follow to ensure success in your overmolding projects.


What is overmolding?


Overmolding is a manufacturing technique that combines two different materials using injection molding. A substrate material, which usually forms the basis of the product, is placed in an injection mold and covered with a second material, the overmolding material. The overmolding material adheres to the substrate material and forms a firm and homogeneous bond. The overmolding material can consist of a hard plastic, thermoplastic elastomers or liquid silicone, for example, depending on the requirements of the product.

Overmolding can be carried out in two different ways: Two-component injection molding or insert molding. In two-component injection molding, both materials are processed in a single mold in a single cycle. The substrate material is injected into the first half of the mold and the overmolding material is injected into the second half of the mold. The mold is then closed and the overmolding material is injected over the substrate material. In two-component injection molding, the substrate material must be made of plastic.

With the insert technique, both materials are processed in two separate molds and cycles. The substrate material is injected in a first mold and then placed in a second mold in which the overmoulding material is injected. The insert technology also allows the substrate material to be selected from materials other than plastic, such as metal, glass or ceramic. The behaviour of the inserted materials during overmoulding can be predicted with the help of injection moulding simulation and thus also optimized for the manufacturing process in an early project phase.



What are the advantages of overmolding?


Overmolding offers numerous benefits that can improve the performance, appearance and cost of your products. Here are some of the key benefits:

  • Increased durability and strength: overmolding can improve the mechanical properties of your products by making them more resistant to wear, corrosion, impact, scratches and breakage. The overmolding material can also act as a protective layer that protects the substrate material from environmental influences. Typical applications include protective covers for electronic devices or the overmolding of magnets as corrosion protection.
  • Improved ergonomics and grip: Overmolding can increase the user-friendliness and comfort of your products by giving them a better grip, flexibility and feel. The overmolding material can also act as insulation, regulating the temperature and vibration of the product. Typical applications include soft components on drill housings or tool handles.
Torque wrench: Soft component made of KEBAFLEX-H/SPA to improve haptics, 2K injection molding with high-strength Grivory GV)
  • Expanded design possibilities and color options: Overmolding can increase the aesthetics and differentiation of your products by allowing you to combine different shapes, textures, patterns and colors. The overmolding material can also serve as decoration or as a functional element, such as buttons, logos or symbols. Typical applications include design elements on tool handles or consumer goods.
ClipClap: Design elements can also be incorporated into products at the prototype stage using the folding process.
  • Function integration: The combination of several materials enables the integration of several functions in one component, e.g. electrical conduction through metallic inserts and electrical insulation through plastic overmolding.
Barlog-Connector: BARLOG Plastics is at your side with extensive experience and simulation methods for overmolding metal inserts)
  • Reduced cost and assembly time: Overmolding can reduce the cost and time of your production by allowing you to integrate multiple components into a single product. Overmolding can also reduce the number of parts, assembly, post-processing and quality control.



What best practices should you follow when overmolding?


To use overmolding successfully, you need to follow some best practices that will ensure the quality and efficiency of your overmolding projects. Here are some of the essential best practices:

  • Material compatibility: selecting compatible materials is critical. Ensure that the substrate and overmolding material adhere well to each other by considering chemical compatibility and bonding capabilities. You can also use special additives or coatings to improve adhesion. In addition, the 2K adhesion can be quantified by producing and testing peel test specimens.
Overview of adhesion-modified KEBAFLEX TPEs and suitable substrate materials
  • Design considerations: Pay attention to the product design. Appropriate design can significantly influence the bond strength between materials. Features such as mechanical crimps, grooves, dimples or edges can also improve bond strength. Also avoid wall thicknesses that are too large or too small, sharp corners or edges that can cause stresses or cracks.
  • Process selection: Choose between two-component injection molding and insert molding based on the needs of your project. Two-component injection molding is efficient for mass production, while insert molding is suitable for lower volumes and complex shapes. Also consider cost, cycle time, mold size and material availability when choosing the process.
  • Surface preparation: For optimal bonding, the surface of the substrate must be clean and properly treated. Contaminants such as dust, oil, grease or moisture can weaken the bond. You can also use different methods to activate the surface, such as plasma, flame, corona or laser.
  • Mold design: Precision in mold design is essential. The mold tool must accommodate both materials and support the overmolding process without defects. Pay attention to the temperature, pressure, speed and time of injection molding to optimize bonding and product quality. Also avoid gaps that are too narrow or too wide, which can lead to material loss or overfilling. When creating injection molds for overmolding, allow sufficient time in the project plan for modification loops to precisely adapt the molds.
  • Testing and prototyping: Prototype testing is essential before mass production. It helps to identify potential problems and ensure that the chosen materials and design work as expected. You can also perform various tests to evaluate the bond strength, dimensional stability, durability and performance of your products.


    Overmolding is a transformative manufacturing process that allows manufacturers to create products that stand out from the competition. By carefully combining two different materials through injection molding, this technique offers unmatched product enhancements. By following these best practices, you can use overmolding to create products that are durable, aesthetically pleasing and functionally superior.

    BARLOG Plastics is your experienced development partner for the realization of overmolding of plastics and metals with other plastics, TPEs or LSR. We are at your disposal as a sparring partner and service provider, from advice on product development and tool design to the simulation of manufacturing processes and the production of prototypes, pre-series and small series.

    In addition to development services, our material experts can also draw on a large pool of suitable hard and soft components for a wide range of applications.

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