Insert Molding: Guide to Custom Parts with Metal Inserts

insert molding services, overmolding services, plastic injection molding

In our daily life, such as threaded inserts and wire plugs, many products consist of metal and plastic inserts. Insert molding becomes the most popular process. Insert molding is used for manufacturing strong, durable, and lightweight parts. Whether your project involves electronic plastic insert injection molding, molded plastic inserts for the automotive industry, or something else industries, Sungplastic experts are ready to help you go from design to production quickly.
And if you are looking for help with your insert injection molding projects, check out this guide to custom items with metal inserts parts.
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What is Insert Molding

Insert molding is a manufacturing process where a pre-formed component, often made of metal or plastic, is inserted into a mold cavity and then encapsulated with molten material, typically plastic. The molten material bonds with the insert, creating a single integrated part with the desired properties and functionalities.
The insert used in the process can be a variety of objects, such as threaded inserts, electrical components, magnets, or even other molded parts. The purpose of insert molding is to combine the advantages of different materials or components into a single part, enhancing functionality, strength, or reducing assembly steps.

Insert Molding vs Overmolding

What is Overmolding:
Overmolding is a distinctive manufacturing process that brings together multiple materials to enhance a part’s aesthetics, functionality, or ergonomics. In overmolding, a second material, called an overmold, is applied onto a pre-existing substrate, typically a plastic or metal component. This can be achieved through insert molding or two-shot molding techniques, offering versatility in material combinations. Overmolding is widely used to create comfortable grips, improve product appearance, introduce sealing properties, or reduce vibrations. The process provides designers with the ability to marry different textures and materials, resulting in visually appealing and user-friendly products across industries like consumer goods, electronics, and medical devices.

Key Differences between Insert Molding & Overmolding:
While both insert molding and overmolding share the goal of integrating multiple materials, they differ significantly in their execution and intended outcomes. Insert molding involves incorporating a pre-formed insert into a plastic mold and injecting plastic around it to create a cohesive part with enhanced structural properties or added functionalities. On the other hand, overmolding applies a second material onto a substrate, offering opportunities for aesthetic enhancements, improved ergonomics, and sealing capabilities. This can involve either encapsulating an existing component or layering materials to create distinct textures and layers. Overall, the choice between these processes depends on specific design goals, such as achieving strength, functionality, or improved user experience, and both techniques play pivotal roles in modern manufacturing.

Insert Molding vs Injection Molding

Insert molding and injection molding are two distinct manufacturing processes that share similarities yet have key differences in their approach and applications. Injection molding is a widely used method for creating plastic parts where molten plastic is injected into a mold cavity, allowing it to cool and solidify into the desired shape. This process is particularly suitable for producing complex, intricate, and high-volume parts with consistent dimensions and surface finish. In contrast, insert molding takes the injection molding concept further by integrating pre-formed components, such as metal inserts or other materials, into the plastic part during the molding process. The insert is strategically positioned within the mold, and molten plastic is injected around it, resulting in a single integrated part that combines the benefits of both materials. While injection molding excels in producing standalone plastic parts, insert molding offers enhanced structural strength, functional integration, reduced assembly steps, and the ability to incorporate multiple materials into a single component. Therefore, the choice between these processes depends on the desired characteristics and functionalities of the final product, with injection molding focusing on plastic part production and insert molding offering added versatility through material integration.

Metal Insert Molding

Metal insert molding is a manufacturing process used to combine metal components with plastic or other materials to create a single integrated part. In this process, a metal insert or component is placed into a mold cavity, and then molten plastic or another material is injected into the mold, encapsulating the metal insert. Once the material solidifies, it forms a strong bond with the metal, creating a finished product that incorporates both metal and plastic elements.

The metal insert can serve various purposes, such as adding structural strength, providing threaded or other functional features, enhancing conductivity, or simply reducing the cost of manufacturing by using less metal. The plastic component can offer design flexibility, reduce weight, and enable the creation of complex shapes that would be challenging or expensive to achieve with metal alone.

Metal insert molding process can be complex, involving precise design considerations, material compatibility, mold design, and production techniques to ensure that the metal and plastic components bond effectively and produce a high-quality final product.
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Plastic Insert Molding

Plastic insert molding is a manufacturing process similar to metal insert molding, but it involves integrating plastic components or parts into a larger plastic component using an injection molding process. In plastic insert molding, a pre-formed plastic insert or component is placed into a mold cavity, and then molten plastic material is injected into the mold, surrounding and encapsulating the insert. Once the plastic solidifies, it forms a cohesive and integrated part where the plastic and insert are fused together.

Careful consideration of material compatibility, insert design, mold design, and molding parameters is crucial to ensure proper adhesion between the plastic and the insert, resulting in a high-quality finished product.
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What is Plastic Threaded Insert

One way insert molding is used is with threaded inserts, which reinforce the mechanical properties of plastic parts’ ability to be fastened together, especially over repeated assembly.

A plastic threaded insert, also known as a threaded insert for plastics, is a type of fastener designed to be embedded or molded into plastic components, providing a reliable threaded connection. It serves as a means to add threads to a plastic part, allowing screws, bolts, or other fasteners to be securely attached. Plastic threaded inserts are commonly used in applications where metal threads might not be suitable due to factors like corrosion, weight, or electrical conductivity.

Plastic threaded inserts are available in various shapes, sizes, and designs, but they typically share some common features:

  • Thread Profile:
    The threaded portion of the insert is designed to match a specific thread size and pitch, enabling it to engage with a corresponding threaded fastener.
  • Body Design:
    The body of the insert is designed to provide stability and secure attachment within the plastic part. It may have features like knurls, flanges, or undercuts to prevent rotation or pull-out.
  • Material:
    Plastic threaded inserts are made from a variety of thermoplastics, such as nylon, polyethylene, or acetal. The material choice is influenced by factors such as strength requirements, temperature resistance, and chemical compatibility.
  • Installation:
    Plastic threaded inserts can be installed using various methods, including heat insertion, ultrasonic insertion, press-fit, or mold-in installation during the plastic injection molding process.
  • Applications:
    Plastic threaded inserts are used in a wide range of industries and applications, including electronics, automotive, consumer goods, medical devices, industrial equipment, and more. They are often used to create secure and durable threaded connections in plastic housings, enclosures, panels, and other components.

Advantages of plastic threaded inserts include corrosion resistance, lightweight design, electrical insulation (non-conductive), and the ability to create strong threads in plastic materials that might otherwise be prone to wear or stripping if metal threads were used directly.

When selecting a plastic threaded insert for a specific application, factors such as the type of plastic, load requirements, environmental conditions, and installation method should be carefully considered to ensure a reliable and effective threaded connection.

Insert Injection Molding Materials

When performing insert injection molding, the selection of materials is crucial to achieving a successful and reliable bond between the insert and the plastic material. Both the insert material and the plastic material must be compatible in terms of thermal properties, adhesion characteristics, and overall performance. Here are some commonly used materials for both inserts and plastic components in insert injection molding:

Insert Materials

  • Metal Inserts:
    Common metals used as inserts include stainless steel, brass, aluminum, and titanium. Metal inserts offer excellent strength, durability, and thermal conductivity.
  • Plastic Inserts:
    Inserts made from thermoplastics compatible with the plastic molding material can be used. These inserts can be molded into the plastic part to enhance specific properties or features.
  • Ceramic Inserts:
    Ceramics are chosen for their high temperature resistance, electrical insulation properties, and corrosion resistance.
  • Other Materials:
    Depending on the application, other materials such as glass, rubber, or composite materials might be used as inserts.

Plastic Molding Materials

The choice of plastic material depends on factors such as the intended application, required mechanical properties, chemical resistance, temperature resistance, and other functional requirements. Common plastic materials used in insert injection molding include:

  • Thermoplastics:
    These plastics can be melted and re-melted multiple times without significant degradation. Common thermoplastics used in insert molding include:
    ABS (Acrylonitrile Butadiene Styrene)
    PA (Polyamide/Nylon)
    PC (Polycarbonate)
    PBT (Polybutylene Terephthalate)
    PP (Polypropylene)
    PEEK (Polyether Ether Ketone)
    POM (Polyoxymethylene)
    HDPE (High-density Polyethylene)
  • Thermosetting Plastics:
    These plastics undergo a chemical reaction during molding and cannot be re-melted once cured. They offer excellent dimensional stability and high-temperature resistance. Examples include:
    Phenolic Resins
    Epoxy Resins
    BMC (Bulk Molding Compound)
  • Liquid Silicone Rubber (LSR):
    LSR is a flexible and heat-resistant material commonly used in medical and electrical applications due to its biocompatibility and electrical insulation properties.
  • Composite Materials:
    Composite materials combine different materials to achieve specific properties. For example, carbon fiber-reinforced plastics offer exceptional strength-to-weight ratios.

Conduct compatibility tests and trials can ensure that the chosen insert and plastic materials adhere well and maintain their integrity during the insert injection molding process. Collaboration with material suppliers and molding experts is essential to optimize the material selection for your specific project and application.

What is an insert mold?

A mold for insert molding, also known as an insert mold or insert molding tool, is a specialized tooling component used in the insert molding process. It is designed to accommodate both the plastic material and the pre-formed insert, allowing them to be combined into a single integrated part during the injection molding process. The mold is a critical element in ensuring the proper encapsulation, positioning, and adhesion of the insert within the plastic component. Here’s an overview of the key features and components of a mold for insert molding:

  • Cavity Design:
    The mold cavity is designed to precisely fit the shape of the desired final part, including the location and orientation of the insert. It defines the exterior shape and features of the molded part.
  • Insert Positioning:
    The mold includes features, such as pockets or slots, to securely hold and position the insert within the cavity. Proper insert positioning is essential for achieving accurate and consistent results.
  • Gate Placement:
    Gates are openings through which the molten plastic is injected into the mold cavity. The gate location is strategically chosen to ensure proper flow of plastic material around the insert and minimize stress concentration.
  • Cooling Channels:
    Channels or passages within the mold allow for the circulation of cooling fluids (typically water) to control the temperature of the mold and solidify the plastic material around the insert.
  • Ejection System:
    Mechanisms, such as ejector pins, are used to remove the finished part from the mold cavity once the injection molding process is complete.
  • Venting:
    Venting features are incorporated to allow air and gases to escape from the mold cavity as the plastic material is injected. Proper venting prevents defects like voids or bubbles in the finished part.
  • Surface Finish and Texture:
    The mold’s interior surfaces can be textured or polished to achieve the desired surface finish of the molded part.
  • Mold Material:
    Mold inserts are often made from high-strength and heat-resistant materials, such as tool steel or aluminum. The choice of material depends on factors like production volume, part complexity, and cost considerations.
  • Heating and Cooling Systems:
    For precise temperature control, molds may have heating elements and cooling channels to maintain consistent thermal conditions during the injection molding process.
  • Runner System:
    The runner system includes channels that direct the flow of molten plastic from the injection molding machine’s nozzle to the mold cavity.
  • Mold Base:
    The mold base provides structural support and houses various mold components. It is typically customizable to accommodate different mold cavities.

Molds for insert molding are carefully designed and engineered to ensure the successful integration of the insert and plastic materials, resulting in high-quality parts with strong bonds and functional capabilities.

Considerations During the Insert Molding Process

The insert molding process requires careful consideration of various factors to ensure successful and high-quality results. Here are some key considerations to keep in mind during the insert molding process:

  • Material Compatibility:
    Ensure that the materials used for the insert and the plastic molding material are compatible in terms of thermal expansion, adhesion, and chemical interactions.
  • Insert Design and Placement:
    Design the insert with features that facilitate proper placement and adhesion within the mold cavity.
    Position the inserts accurately to achieve the desired functionality and appearance of the final part.
  • Mold Design:
    Design the mold with features that allow for secure placement and uniform encapsulation of the insert.
    Incorporate features to prevent rotation or movement of the insert during the molding process.
  • Insert Surface Preparation:
    Properly clean and prepare the surfaces of the insert to promote adhesion with the plastic material. This may involve surface treatments or coatings.
  • Molding Parameters:
    Optimize molding parameters such as temperature, pressure, injection speed, and cooling time to ensure proper encapsulation of the insert and minimize defects.
  • Mold Temperature Control:
    Maintain consistent mold temperatures to prevent warping, improve material flow, and ensure proper adhesion between the insert and plastic.
  • Insert Orientation and Orientation Pins:
    Consider incorporating orientation features, such as pins or keyways, to ensure the correct orientation of the insert during molding.
  • Gate Location:
    Choose appropriate gate locations to facilitate the flow of molten plastic around the insert while minimizing stress concentration or damage to the insert.
  • Cooling Time:
    Determine the optimal cooling time to ensure that the plastic material solidifies fully around the insert without causing deformations or defects.
  • Cycle Time and Production Volume:
    Balance the cycle time of the molding process with the desired production volume, taking into account factors such as mold cooling, insert placement, and material curing.
  • Quality Control and Inspection:
    Implement quality control measures to monitor the integrity of the insert-to-plastic bond, ensuring that the insert is properly encapsulated.
    Perform visual inspections and, if necessary, non-destructive testing to verify the quality of the finished parts.
  • Post-Processing:
    Plan for any necessary post-processing steps, such as trimming excess material or performing additional finishing operations.
  • Design for Manufacturability:
    Consider design modifications that optimize the insert molding process, such as simplifying part geometry or adjusting material selections.

By carefully addressing these considerations, it can achieve successful insert molding outcomes, producing high-quality parts with reliable insert-to-plastic bonding and functional integration.

Insert Molding Process

The insert molding process involves integrating pre-formed components, such as metal inserts or other materials, into a plastic part during the injection molding process. This creates a single integrated part with the benefits of both materials. Here’s an overview of the insert molding process:

  • Part Design and Selection:
    Determine the type and design of the insert components that will be incorporated into the plastic part. These inserts could be metal, plastic, ceramics, or other materials, depending on the application requirements.
    Design the plastic part and mold to accommodate the insert and provide proper clearance and adhesion features.
  • Mold Design:
    Create a mold that includes cavities for both the plastic material and the insert.
    Design the mold with features that help secure and position the insert properly during the molding process.
  • Insert Placement:
    Position the pre-formed inserts within the mold cavities according to the design specifications. These inserts are typically placed manually or using automated equipment.
  • Mold Closing and Injection:
    Close the mold to create a sealed cavity.
    Molten plastic material is injected into the mold under high pressure through the injection molding machine’s nozzle. The plastic material flows around and encapsulates the insert.
  • Molding and Cooling:
    The plastic material cools and solidifies around the insert, forming a strong bond.
    Cooling time is crucial to ensure the plastic solidifies properly and maintains its shape.
  • Mold Opening and Ejection:
    The mold is opened, and the newly molded part, which now includes the integrated insert, is ejected from the mold cavity.
    The part may undergo additional cooling or post-processing steps to further enhance its quality.
  • Trimming and Finishing:
    Excess material, known as flash, is removed from the molded part.
    Any additional finishing steps, such as surface texturing or painting, may be performed as needed.

Advantages of Insert Molding

Insert molding offers several advantages in various industries and applications. Some of the key benefits include:

  • Enhanced Strength and Durability
    By incorporating metal, plastic, or other materials into the molding process, insert molding can significantly improve the strength and durability of the final product. This is particularly useful in applications where the part is subjected to mechanical stresses or heavy use.
  • Reduced Assembly Steps
    Insert molding allows multiple components to be combined into a single integrated part. This can eliminate the need for additional assembly steps, reducing labor costs, assembly time, and the potential for errors.
  • Complex Geometries
    The process enables the creation of complex shapes and designs that might be difficult or costly to achieve using other manufacturing methods. This is especially advantageous when intricate features or contours are required.
  • Functional Integration
    Insert molding allows for the integration of functional features such as threaded inserts, electrical contacts, or mounting points directly into the molded part. This can streamline assembly and improve the overall functionality of the product.
  • Material Savings
    By using inserts strategically placed within the mold, less material is required to achieve the desired strength and functionality, which can lead to cost savings.
  • Improved Aesthetics
    Insert molding can create a seamless appearance by hiding fasteners or structural elements that would otherwise be visible in an assembly. This results in a more polished and aesthetically pleasing final product.
  • Reduced Weight
    By incorporating lightweight materials or utilizing a combination of materials, insert molding can help reduce the overall weight of the finished part, making it more suitable for applications where weight is a concern.
  • Enhanced Heat and Electrical Properties
    Insert molding can be used to combine materials with different thermal or electrical properties, creating parts that can handle a wide range of operating conditions.
  • Cost Efficiency
    While there may be initial setup costs associated with mold design and production, insert molding can lead to long-term cost savings through reduced assembly time, fewer components, and improved production efficiency.
  • Streamlined Production
    Insert molding can lead to faster and more efficient production processes since multiple components can be molded together in a single step.
  • Versatility
    Insert molding can be applied to a wide range of materials, including metals, plastics, ceramics, and more, making it a versatile process suitable for various industries and applications.

Applications of Insert Molding

Insert molding is used in a wide range of industries and applications where the combination of different materials or components is beneficial. Some common applications of insert molding include:

  • Automotive Industry:
    Electrical connectors and components with embedded metal pins or terminals.
    Interior and exterior trim components with integrated fasteners or mounting points.
    Seals and gaskets with embedded metal reinforcement.
  • Electronics and Electrical Appliances:
    Enclosures and housings with embedded electronics, connectors, or components.
    Keyboards and remote controls with integrated buttons or switches.
    Sensors and connectors with metal contacts.
  • Medical Devices:
    Surgical instruments with embedded metal components for strength and precision.
    Catheters and medical tubing with embedded sensors or markers.
    Disposable medical devices with integrated features.
  • Consumer Goods:
    Power tool handles with embedded grip materials or vibration dampening.
    Household appliances with integrated electronic controls and displays.
    Wearable devices with sensors and connectors.
  • Aerospace and Defense:
    Avionics components with embedded connectors and sensors.
    Military equipment with integrated electronic and mechanical elements.
    Aerospace parts with embedded reinforcements for strength.
  • Industrial Equipment:
    Machinery components with integrated bearings, bushings, or inserts.
    Equipment handles and grips with embedded materials for comfort and durability.
    Fluid handling systems with embedded seals and connectors.
  • Telecommunications:
    Networking equipment with integrated connectors and ports.
    Fiber-optic connectors with precision-molded components.
    Handheld devices with embedded antennas and connectors.
  • Packaging:
    Packaging components with embedded RFID tags or sensors.
    Packaging closures with integrated tamper-evident features.
  • Toys and Recreational Products:
    Toy components with integrated electronic or mechanical elements.
    Sporting equipment with embedded grips, handles, or connectors.
  • Energy and Power Generation:
    Electrical components with integrated connectors, terminals, or insulators.
    Alternative energy equipment with embedded sensors or connectors.

Custom Insert Molding Services: Make Custom Insert Molded Parts

At Sungplastic, various material are provided and we have built good relationships with local and abroad material suppliers and can custom the raw material that you need. We provide custom, design, prototyping and plastic molding services. Sungplastic’s experienced staff are experts at the custom insert molding process. We have the capability to take insert injection materials and create plastic injection inserts from those materials. Our expert knowledge and advanced techniques and responsible professionals paired with our members’ commitment to customer service mean you will get the best products on the market for the absolute best price.

Get in touch with us today and let us help you with all your insert molding needs today.

About Sungplastic

About Sungplastic

Sungplastic is a plastic product manufacturer with rich experience in injection molding. According to the different product development requirements, we flexibly adjust the manufacturing process to achieve high quality, high efficiency and more economical.

We offer a variety of manufacturing services: Rapid Prototyping, Tool Making, Injection Molding, Product Design and Development, CNC Machining and Metal Stamping. You can choose from a variety of plastics, silicone rubber, or metal for your product. Regardless of mass production or small batch customization, Sungplastic has always been committed to providing assured, efficient and more economical one-stop processing services for your projects.

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