Insert Molding: What is it?

Insert molding is a specialized injection molding process where pre-formed components, often made of metal or other materials, are placed into the mold before the plastic is injected. This process integrates multiple materials into a single molded part, enhancing functionality and reducing the need for secondary operations. Insert molding is widely used in industries such as automotive, medical devices, electronics, and consumer goods.

This blog explores the options and variations available in insert molding.

How Insert Molding Works

Insert molding involves placing a pre-formed component (like metal or another plastic) within a mold cavity before injecting molten plastic. This encapsulates the insert, creating a single, integrated part with enhanced functionality and strength.

Typically, if you are including inserts with your parts, your mold or tooling for production will need to be adjusted. The extent of the mold modifications will vary depending on the complexity of the insert and, of course, the specific requirements of the application. In some cases, minor modifications may be sufficient, while in others, more extensive changes may be necessary.

Your tool designer will need to:

1. Insert Locating Features: The mold must incorporate features to accurately and securely locate and hold the insert in place during the injection molding process. These features can include:
   • Locating pins: to position the insert within the cavity.
   • Detents: these prevent the insert from shifting during injection.
   • Undercuts: these lock the insert securely in the mold
2. Consider Material Flow: The mold design must ensure that the molten plastic flows smoothly around the insert, completely encapsulating it without creating voids or air pockets. Modifications to the cavity shape or the injection gate location may be needed to prevent air pockets.
3. Include Cooling Channels: The mold must include appropriate cooling channels to ensure efficient heat dissipation and rapid solidification of the plastic around the insert.

The insert molding process is then as follows:

1. Insert Placement: The insert, typically made of metal (like steel, brass, or aluminum), ceramic, or another suitable material, is precisely positioned within the mold cavity. For simpler inserts and lower production volumes, inserts may be manually placed into the mold cavity. For higher volumes and increased precision, automated systems using robots or specialized equipment are often employed.
2. Plastic Injection: As with a regular injection molding process, molten plastic is then injected into the mold cavity under high pressure. This will completely encapsulate the insert.
3. Cooling and Ejection: The mold is then cooled, allowing the plastic to solidify around the insert. Once cooled, the mold opens, and the finished part, with the insert securely embedded, is ejected.

Materials Used

• Plastic Resins: Most, if not all injection molding materials can be used for producing parts with inserts. These include a variety of thermoplastics such as ABS, polycarbonate, polyethylene, and polypropylene. Your choice depends on the end application’s requirements for durability, heat resistance, and flexibility, rather than the type of insert you wish to incorporate.
• Insert Materials: Common insert materials include metals (e.g., brass, steel, aluminum), ceramics, and even pre-molded plastic components. The inserts are typically chosen for their mechanical strength, conductivity, or other functional properties.

Why Use Inserts?

Insert molding offers a range of advantages, making it a preferred choice for many applications. Integrating metal inserts significantly enhances the strength, rigidity, and durability of plastic components, while also providing crucial functionalities such as threads, electrical contacts, or bearings—eliminating the need for separate assembly steps. By embedding components during the molding process, it reduces labor costs and improves efficiency by eliminating separate assembly operations. Additionally, insert molding creates aesthetically pleasing components with contrasting materials and finishes, combining functionality with visual appeal.

Common Types of Inserts

• • Threaded Inserts: These are often used to create durable threaded holes in plastic parts for screws or bolts.
  • Electrical Components: Items like pins, connectors, or terminals are embedded to enhance electrical performance.
  • Custom Shapes: Custom-designed inserts can include magnets, bushings, or specific geometries tailored to the product’s needs.

Design and Production Considerations

Insert size and shape must be carefully considered to minimize movement during the molding process, with proper tolerances being critical. The mold design is crucial, ensuring it securely holds the insert in place to prevent displacement during plastic injection. Material compatibility between the plastic and the insert is also essential to ensure a strong bond and avoid thermal or mechanical stresses.

Of course, your supplier has some obligations when it comes to insert molding and consistent, high-quality results. These go beyond precise control of injection pressure, temperature, and cooling rates. There should be quality procedures in place which will guarantee your part integrity, as well as ensuring insert production meets your specific criteria. As we’ve noted that insert molding can be more cost effective than manual assembly, your supplier should provide you with detailed cost analysis of not only tooling costs, but also other potential challenges that could arise during the manufacturing process.

Applications

We’ve explored why it would be beneficial to include inserts in some injection molded production parts. Here’s a quick rundown of where or why those parts might be used. The list here also indicates some of the project capabilities from Quickparts.

• Automotive: Creating lightweight yet robust components, such as gears with metal cores, or engine mounts, fuel injectors, sensors and electrical connectors.
• Medical Devices: Producing parts like needle hubs or surgical instruments where precision and reliability are essential. Insert molding is also commonly used when creating diagnostic equipment, including x-ray and MRI machines. More recently, insert molding has been crucial in the development of parts for medical robots.
• Electronics: Manufacturing parts like connectors, where electrical components need to be securely embedded in plastic housings, as well as the housings themselves.
• Consumer Goods: Insert molding is common in the production of most household appliances, from refrigerators to shower units, as well as toys and sports equipment.

In Conclusion

Insert molding is a versatile manufacturing process that combines the benefits of different materials into a single, functional component. By carefully selecting materials, inserts, and placement techniques, manufacturers can produce high-quality parts tailored to their specific needs. Whether you’re in the automotive, medical, or electronics industry, insert molding provides a reliable and cost-effective solution for complex manufacturing challenges.