Insert Molding: Understanding of the Metal or Non-metal Insert for Plastic Injection Molding

What Is Insert Molding?


In modern manufacturing, numerous products incorporate both metal and plastic components. Among the various production methods available to achieve this integration, insert molding stands out as the most widely used solution.

Insert molding is a specialized plastic injection molding process where a pre-formed component, often made of metal or another material, is inserted into the mold cavity before the plastic material is injected. The molten plastic then bonds to or around the inserted component, creating a single integrated part.

Overview Of The Insert Molding Process:


  1. Material Selection:
  • The process begins with selecting the appropriate plastic material based on the desired characteristics of the final part, such as strength, flexibility, heat resistance, or electrical properties.
  • The choice of plastic must also consider its compatibility with the insert material.
  1. Insert Preparation:
  • Inserts can be made of various materials, including metals (e.g., brass, steel, aluminum), plastics, ceramics, or even other composite materials.
  • Inserts may be pre-manufactured components, like threaded inserts, stamped metal parts, or even electronic components.
  1. Mold Design:
  • The mold used in insert molding is typically more complex than a standard injection mold.
  • It includes features to securely hold the inserts in place during the injection process, ensuring proper positioning.
  • Mold design also considers factors like gate placement and venting to prevent air pockets or defects in the final part.
  1. Insert Placement:
  • Depending on the design, inserts are manually or automatically placed into the mold cavities or onto cores before the injection phase.
  • Robotics and automation systems are often used for precise and consistent insert placement.
  1. Injection:
  • Molten plastic is injected into the mold at high pressure.
  • The plastic flows around and encapsulates the inserts, forming a strong bond during the cooling phase.
  1. Cooling:
  • The mold is cooled to solidify the plastic and ensure it securely bonds to the inserts.
  • Proper cooling is crucial to prevent warping or distortion of the final part.
  1. Ejection:
  • Once the plastic has cooled and solidified, the mold opens, and the completed part is ejected.
  • Care is taken to avoid damaging delicate inserts during ejection.
  1. Post-Processing:
  • Some insert-molded parts may require additional post-processing steps, such as trimming excess plastic or secondary operations like machining.


Advantages of Insert Molding:


  1. Cost Efficiency:
    • Reduced Assembly Costs: One of the primary advantages of insert molding is its potential to significantly reduce assembly costs. By integrating multiple components into a single part, manufacturers eliminate the need for additional assembly steps, reducing labor and time costs.
    • Lower Scrap Rates: Fewer individual parts to assemble mean fewer opportunities for defects, which can reduce scrap rates and improve overall production efficiency.
    • Material Savings: Combining parts can lead to material savings, especially when considering scrap material generated during traditional assembly processes.
  2. Enhanced Strength:
    • Strong Bonding: Insert molding creates a robust bond between the insert and the plastic material. This bonding results in increased part strength, making it ideal for applications requiring durability and structural integrity.
    • Metal Inserts: For applications requiring metallic characteristics, such as electrical conductivity or high tensile strength, metal inserts can be effectively incorporated into plastic parts.
  3. Precision:
    • Accurate Positioning: Insert molding allows for precise positioning of inserts within the mold, ensuring that components are precisely located where needed in the final part.
    • Tight Tolerances: The process enables the production of parts with tight tolerances, meeting specific design requirements.
  4. Complex Geometries:
    • Design Flexibility: The integration of inserts within plastic parts facilitates the creation of complex geometries and designs, enhancing product functionality and aesthetics.
    • Weight Reduction: Lightweighting can be achieved by combining strong inserts with lightweight plastics.

Considerations for Insert Molding:


  1. Material Compatibility:
    • Thermal Compatibility: The thermal properties of the plastic and the insert material must be compatible to prevent issues such as warping, cracking, or poor bonding.
    • Chemical Compatibility: Ensure that the plastic and insert materials are chemically compatible to avoid degradation or undesirable reactions.
  2. Insert Positioning:
    • Precision: Accurate positioning of inserts within the mold is crucial for proper functionality. Deviations can lead to defects or part failures.
    • Automation: Robotic or automated systems are often used to achieve consistent insert placement.
  3. Mold Design:
    • Secure Holding: The mold must be designed to securely hold inserts in place during the injection process to prevent shifting or misalignment.
    • Venting and Gating: Proper venting and gating design are essential to prevent air pockets or defects around the inserts.
  4. Part Complexity:
    • Complexity vs. Cost: While insert molding offers design flexibility, overly complex designs can increase tooling and production costs.
    • Part Removal: Delicate or intricate parts may require careful handling during ejection to prevent damage to the inserts.
  5. Post-Processing:
    • Trimming: Some insert-molded parts may require trimming excess plastic to meet precise tolerances or aesthetics.
    • Secondary Operations: Additional machining or assembly steps may be needed for specific applications.

Understanding these advantages and considerations is essential for successfully implementing insert molding in various manufacturing processes. Proper planning, material selection, mold design, and quality control are key factors in achieving consistent and high-quality results.

Applications of Insert Molding:


  1. Automotive Industry:
    • Electrical Connectors: Insert molding is widely used in the automotive sector for producing electrical connectors. Metal pins and terminals can be securely encapsulated within plastic housings, ensuring reliable electrical connections.
    • Sensors: Automotive sensors, such as those used for airbags, engine management, and safety systems, often employ insert molding to protect delicate sensor components and enhance their durability.
    • Interior Components: Overmolding metal or plastic components with softer materials can improve the look and feel of interior parts like steering wheel grips, gear shift knobs, and dashboard controls.
  2. Electronics:
    • Connectors and Cables: Many electronic connectors, cable assemblies, and wire harnesses benefit from the strength and durability offered by insert molding. This process ensures secure connections and protects delicate wires.
    • Housings: Electronic devices often require custom housing solutions. Insert molding allows for the incorporation of features like snap-fit connectors, mounting points, and strain reliefs.
  3. Medical Devices:
    • Medical Connectors: In medical applications, precision and reliability are paramount. Insert molding is used for producing connectors and cable assemblies for medical devices, ensuring secure and sterile connections.
    • Syringe Components: Syringe barrels and plunger components are often created using insert molding. This process ensures precise alignment and airtight seals.
  4. Consumer Goods:
    • Tool Handles: Overmolded tool handles provide ergonomic grips and improve user comfort and safety. The combination of metal or plastic cores with softer overmolding materials results in durable and comfortable handles.
    • Toothbrushes: Toothbrushes often incorporate plastic bristle holders or metal parts for structural support, which are seamlessly integrated through insert molding.
    • Appliance Components: Various components in appliances, such as washing machine lids, dishwasher spray arms, and refrigerator door handles, benefit from the strength and design flexibility offered by insert molding.
  5. Industrial Equipment:
    • Valves and Fittings: Industrial valves, fittings, and couplings can be manufactured using insert molding techniques to ensure leak-proof and durable connections.
    • Pneumatic and Hydraulic Components: The combination of metal and plastic parts in pneumatic and hydraulic systems is achieved through insert molding for enhanced functionality and reliability.
  6. Aerospace and Defense:
    • Connectors and Enclosures: Critical aerospace and defense applications often require custom connectors and enclosures that can withstand extreme conditions. Insert molding allows for the integration of specialized features and materials.
    • Instrumentation: Sensitive instruments and sensors used in aerospace and defense applications can be protected and secured within plastic or composite housings using insert molding.
  7. Telecommunications:
    • Connectivity Components: In the telecommunications industry, connectors, cable assemblies, and enclosures are commonly produced using insert molding to ensure robust and reliable connections in various environments.

Insert molding’s versatility and ability to combine materials make it suitable for a wide range of industries and applications. Its advantages in terms of strength, precision, and design flexibility continue to drive its adoption in various manufacturing processes.

Your Custom Insert Molding Solution Provider


After addressing the critical aspects for insert molding, it is obvious that this manufacturing process can be quite complex. Therefore, it is wise to partner with a professional and dependable injection molding specialist like GEMS-MFG. Our company offers a comprehensive suite of insert molding services designed to guarantee that your components not only meet all specifications but also adhere to strict production timelines.


GEMS-MFG can evaluate your design thoroughly and provide you with a comprehensive design for manufacturability analysis and accompanying report. Simply forward your design files to us, and you can expect prompt and trustworthy feedback. With our dedicated engineering team, strong insert molding capabilities, and unwavering commitment to stringent quality inspection standards, we are primed to deliver exceptional results for your projects. Do not hesitate to reach out to us now to start your upcoming project; we are prepared to support your new product development with our full efforts.


Integrated Factory Resources

We are your one-stop manufacturing solution provider for customized products with the joint effort & support from our 120 partnership subcontractors mainly for the production of metals & plastics. We can expand much faster but the top management decide to keep GEMS a compact, dedicated and professional company, which allows our team to really focus and deliver on your projects without any excuse or compromise. We strive to be a long-term, reliable and trustworthy partner of our customers rather than just being a contractor, and look forward to growing the company with customers’ success.

Manufacturing Veteran Team

With the passing years, we are proud to build up a manufacturing veteran team with rich experience and full expertise to fulfill your specific demand. From mold making, injection molding, die casting, stamping and sheet metal, to 2nd processes like CNC machining, oil spraying, powder coating and chrome plating, and then assembling and packaging and related, we always have someone in house to be an expert to resolve the issues in different stages of product development. We also specialize in providing charger, cable and hub, plus other electronic accessories that support a complete set of product.

Strong Project Management

“Think global, execute local” is the principle of our work. Time, quality and cost are the three key elements to be considered throughout the product development from concept design to mass production. A detailed plan with weekly conference call update is a critical gateway to ensure these three key elements are successfully implemented, also assuring that all parties are on the same page. Communication is the Secret to Success . Everyone works independently to take care his own job, but together we are a team to get things done and are your daily eyes and ears onsite in China.

Flexible Operation & Customization

We offer a wide variety of products, such as mold, component and assembly product, and certain value-added services. For logo or branding product, we have in house resources to complete a color mix that can perfectly match a brand’s unique colors in fast and cost-effective way. Understood the client needs production parts but having a hard time to find a vendor since the order quantity is as low as 1000 or lower. GEMS is well set up for low volume injection molding or die casting projects. Surely our team is also capable of building SPI Class 101 mold that is designed & made for 1 million cycles or more of producing the same high quality parts consistently.