What Is Insert Molding? Process Types, Types and Applications

Insert molding technology is a technology that embeds inserts made of metal, plastic or other materials into plastic or other base materials to form a composite structure. This technology plays an important role in the field of CNC machining , especially in improving product performance and reducing costs . This article will discuss the process flow, types and practical applications of insert molding in detail.

What is Insert Molding?

Insert molding is a plastic molding process that is usually used to accurately embed inserts of metal, ceramic or other high-strength, high-conductivity materials into plastic parts to enhance the structural strength, conductivity or heat resistance of plastic parts. This process has been widely used in many fields such as automobile manufacturing, electronic equipment production, consumer goods manufacturing, etc., providing strong support for the manufacture of high-quality, high-performance products.

Insert Molding Process

The insert molding process mainly includes the following key steps:

Step 1: Preliminary Preparation

Select appropriate insert materials (such as metal, ceramic, etc.) according to product design requirements, and perform pretreatment, including cleaning, degreasing, rust removal and rust prevention, to ensure that the insert surface is clean and pollution-free.

Design and manufacture special injection molds to ensure the accurate positioning and stable fixation of the insert in the mold, and that the plastic material can evenly and fully fill the mold cavity.

Step 2: Insert Placement and Mold Assembly

The pre-treated insert is placed precisely at the predetermined position of the mold according to the design requirements to ensure that the insert will not shift or deform during the molding process.

If required, inserts are automatically or manually loaded into the mold, ensuring accuracy and consistency.

Step 3: Injection Molding

The molten plastic material is injected into the mold cavity so that it fully surrounds the insert and fills the entire mold. During the injection molding process, parameters such as injection temperature, pressure, speed and holding time are strictly controlled to ensure that the plastic material and the insert are tightly combined and solidified.

Step 4: Cooling and Demoulding

After injection molding, the mold and the plastic parts are allowed to cool naturally or forced to cool to completely solidify the plastic material. After cooling, the mold is opened and the plastic parts are carefully removed for post-processing such as deburring and trimming to improve the surface quality and aesthetics of the product.

Step 5: Post-machining and Quality Inspection

Separate the molded part from the gate and make any necessary cuts or trims. Post-machining steps such as deburring, heat treatment, surface preparation and moisture control are performed to further improve the performance and appearance of the component.

Carry out quality inspection to ensure the close integration of the insert and the plastic matrix and that the overall performance of the product meets the design requirements and quality standards.

What are the Types of Insert Molding?

Metal Insert Molding:

Metal insert molding is one of the most common types of insert molding, which uses inserts made of metal materials such as brass, stainless steel, aluminum, etc. These metal inserts are precisely placed in the mold and then injected with molten plastic for molding. Metal inserts not only enhance the structural strength of plastic parts, but also provide electrical conductivity and heat resistance, so they are widely used in the automotive, electronics, and aerospace industries.

Ceramic Insert Molding:

Ceramic insert molding utilizes the high temperature resistance, wear resistance and corrosion resistance of ceramic materials and integrates them into plastic parts. This molding method is often used for plastic parts that need to withstand high temperatures or corrosive environments, such as chemical equipment and medical devices. The introduction of ceramic inserts enables these parts to maintain stable performance under harsh working conditions.

Plastic Insert Molding:

Plastic insert molding is a process that integrates small plastic parts as inserts into larger plastic objects. This type of molding is very useful when manufacturing products with complex structures, such as the front cowl on a boat hull. Through plastic insert molding, a strong bond between different plastic materials can be achieved, improving the overall performance and durability of the product.

Glass Insert Molding:

Glass insert molding is a process that integrates glass inserts into plastic molds. Unlike injection molding, glass injection molding is usually used to produce smaller glass parts. Glass inserts provide transparency to the product and help create specific shapes and designs. This molding method has a wide range of applications in optical instruments, decorative items, and more.

Silicone Insert Molding:

Silicone insert molding uses silicone as the molding material, which is formed by combining a flowable silicone resin with a base resin and then injecting it into a mold. After a heating and cooling cycle, the silicone solidifies and tightly bonds with the plastic part. Silicone insert molding has excellent flexibility, high temperature resistance, and chemical corrosion resistance, so it is widely used in medical, electronic, and automotive fields.

Cavity Insert Injection Molding:

Cavity insert molding is a special type of insert molding in which the mold cavity is composed of two movable one-piece injection mold cavity halves. The two mold components are connected by a hinge and remain tightly fitted during the injection molding process. This molding method is suitable for manufacturing plastic parts with complex geometries and precise dimensional requirements.

Insert Compression Molding:

Insert compression molding is a type of insert molding used to make custom plastic parts. It involves injecting plastic into a mold and then removing excess resin through compression. Once the mold is opened, the part can be demoulded. This molding method is suitable for making plastic parts with high precision and complex shapes.

Film Insert Molding:

Film Insert Molding is a process similar to insert molding, but a thin layer of plastic film is placed around the product during the molding process. This film effectively isolates the metal insert from the product, preventing them from direct contact. Film Insert Molding is significant in protecting the metal insert from corrosion and wear, while also contributing to the overall aesthetics and durability of the product.

Insert Molding Materials

Insert molding technology involves a variety of material selections, which depend on mold characteristics, product requirements, and other factors such as chemical adhesion, manufacturing process, mechanical adhesion, and product wall thickness. The following is a description of the various types of insert molding materials:

Thermoplastics:

Thermoplastics are considered environmentally friendly materials due to their reusability. They excel in the plastic molding process, are chemically resistant, and ensure uniformity and gloss in the product.

The most commonly used thermoplastic materials on the market include polyethylene (HDPE, MDPE, LDPE), which are lightweight, chemically resistant, hard, and impermeable; polystyrene, which is transparent, flexible, and has a low melting point, suitable for consumer products and medical devices; and nylon, a long-lasting material that is chemically and abrasion resistant and replaces metal in heavy-duty applications due to its high melting point.

Elastomer:

Elastomers include rubber and various synthetic and natural polymers and are favored for their flexibility and recyclability. They are a very environmentally friendly material, ideal for home appliances and automotive manufacturing. Liquid rubber silicone is highly resistant to wear and heat and is a flexible, lightweight rubber-like substance that can be used to create products with complex geometries. Natural rubber is durable and flexible and is often used to make tires and other household items.

Glass:

Glass is another important material in insert molding. It has a high coefficient of thermal expansion and high viscosity, is heat-resistant and not prone to corrosion. Glass acts as a barrier between metal and plastic, preventing them from affecting each other. In addition, glass can also be used to make metal objects, and its unique properties make it widely used in insert molding.

Metal Materials:

Metal materials play an important role in insert molding. They are widely favored for their high strength, high hardness, excellent electrical and thermal conductivity.

Common metal materials cover a variety of types, such as carbon steel, which is affordable and durable. Although it is prone to corrosion, it is widely used in industries such as construction and roads.

Stainless steel, with its corrosion resistance, oxidation resistance, high strength and beautiful appearance, has become the first choice for marine engineering, underground pipelines and other occasions that require high corrosion resistance.

Aluminum alloys are widely used in the connection system of light steel keels due to their light weight and good corrosion resistance.

Although copper alloys have different thermal expansion coefficients from plastics, resulting in relatively weak bonding, their high mechanical strength, rust-proof and easy processing characteristics still make them irreplaceable in specific fields.

Ceramic Materials:

Ceramic materials have excellent resistance to high temperatures, wear and corrosion, and are often used in plastic parts that need to withstand high temperatures or corrosive environments, such as chemical equipment and medical devices.

Advantages of Insert Molding

Production Cost Savings:

The insert molding process significantly reduces production costs by combining the molding and secondary manufacturing stages into one step. Traditional injection molding requires additional manufacturing processes to connect inserts of different materials after molding, while insert molding eliminates this step. This not only reduces the demand for manpower, factory space and management capabilities, but also reduces overall manufacturing costs, making production more efficient and economical.

Optimum Material Utilization:

Insert molding allows manufacturers to integrate two or more materials into a single end product, optimizing the impact of material properties. This process enables manufacturers to use the most expensive materials, such as metal inserts, in the most critical areas, while using more economical and lighter materials, such as plastics, in other areas. This saves costs while reducing the weight of the product and improving overall performance.

Enhanced Structural Integrity:

Insert molding produces material bonds that are far superior to standard molding, machining and assembly methods. Through the creative use of design elements such as undercuts and shoulders, metal inserts such as threaded brass inserts are better able to withstand torque and tension. In contrast, traditional methods such as heat staking and ultrasonic insertion cannot fully integrate the insert into the parent material, thus affecting structural integrity.

Aesthetic Enhancement:

Insert molding not only focuses on the performance and function of the product, but also its aesthetic value. Insert molding can produce aesthetic effects by injection molding molten plastic around any substrate or insert. Compared with products made of structural steel, insert molded products have a smoother and more refined appearance and texture. This aesthetic improvement makes insert molding more competitive in consumer products and high-end markets.

Complementary Performance

Insert molding allows the easy formability and elasticity of plastics to be combined with the rigidity, strength and heat resistance of metals to complement each other, thereby producing complex and sophisticated metal-plastic integrated products. This combination not only reduces the size and weight of the product, but also meets the basic functional requirements of electrical products, such as electrical conductivity and magnetic conductivity. In addition, insert molding can also meet certain special requirements, such as wear resistance and fastening, providing greater flexibility and diversity for product design.

Improved Production Efficiency:

Insert molding can combine the insert with the plastic in one molding process, avoiding secondary processes such as hot melting, welding and riveting. The combination of vertical injection molding machine, robot, insert product arrangement device, etc. makes the insert molding project mostly automated, further improving production efficiency and accuracy.

Insert Molding Applications

1. Automobile Industry

Insert molding is widely used in the automotive industry, especially in the field of new energy vehicles. With the trend of integration and high voltage of new energy vehicles, the insert molding process achieves mutual insulation of key metal parts by injecting metal conductors into plastics, thereby reducing safety hazards. This process is ideal for sealing wires and electronic connectors to plastic housings. In addition, the traditional automotive industry also uses insert molding to manufacture key components such as engine components and chassis components to improve product reliability and durability.

2. Consumer Electronics Industry

Insert molding also plays an important role in the consumer electronics industry. Threaded inserts and wire plug encapsulation are typical applications of insert molding in this industry, which provide strong and reliable connections for consumer electronic devices. In addition, insert molding is also used to produce digital control panels and components, providing the equipment with an aesthetic and functional appearance. At the same time, the insert molding process is also widely used in the manufacture of electrical knobs and military equipment, etc., meeting the consumer electronics industry’s demand for high-precision and high-quality components.

3. Aerospace Industry

In the aerospace field, the insert molding process is mainly used to manufacture key components such as aircraft seats, luggage compartment latches, lavatories, handles and user interface switches. These parts require not only high strength and durability, but also precise size and shape. Through the insert molding process, the accuracy and reliability of these parts can be ensured, thus meeting the high performance and high precision requirements of the aerospace field.

4. Medical Industry

The medical industry also has extremely high requirements for the precision and safety of parts, and the insert molding process is one of the ideal choices to meet these requirements. From simple medical devices to complex medical implants, the insert molding process plays an important role in the medical industry. For example, tubes, dental instruments, medical knobs, blades, surgical instruments and medical housings can all be manufactured using the insert molding process. These parts require not only high precision and high quality, but also good biocompatibility and corrosion resistance.

5. Defense Industry

In the defense industry, insert molding helps produce cost-effective, efficient, and lightweight precision military equipment. For example, handheld communication devices, weapons, battery packs, ammunition, and binoculars and monocular housings can all be manufactured using insert molding. These parts require not only high precision and quality, but also stable performance in harsh environments. Through the insert molding process, the accuracy and reliability of these parts can be ensured, thus meeting the defense industry’s demand for high-quality parts.

How to Design Insert Molding?

Designing for insert molding is a complex and delicate process, here is a brief description:

1. It is necessary to determine the type, shape, size, position and function of the insert in the plastic product. Common insert types include metal inserts, plastic inserts, etc. The shape and size are determined according to the specific product requirements.

2. Design the mold. The mold design needs to consider the positioning and fixation of the insert and the flow path of the plastic melt. The insert must be accurately placed in the mold to ensure that the plastic melt can completely wrap the insert and form a tight bond during injection molding. At the same time, the mold gate position, number and size must also be reasonably designed to ensure uniform flow and sufficient filling of the plastic melt.

3. It is necessary to select appropriate injection molding materials and injection molding process parameters. The selection of injection molding materials needs to consider factors such as fluidity, shrinkage, and heat resistance to ensure the quality and performance of plastic products. Injection molding process parameters include injection molding temperature, injection molding pressure, injection molding speed, etc. These parameters need to be reasonably adjusted according to the injection molding material and mold structure.

4. Conduct trial production and testing. During the trial production process, it is necessary to pay close attention to the bonding between the insert and the plastic melt, the shrinkage of the plastic product, and the wear of the mold. During the testing phase, various performance tests are required on the plastic product, such as tensile strength, bending strength, impact strength, etc., to ensure that it meets the design requirements.

Insert Molding vs Overmolding

Core material: The core material of insert molding is more diverse, including metal, cloth, paper and other materials; while the core of over-molding is mostly plastic parts or semi-finished parts.

Application purpose: Insert molding focuses more on the combination of metal and plastic to meet the requirements of electrical, strength, heat resistance, etc., while over-molding focuses more on improving the aesthetics, processing characteristics and other physical properties of plastic parts.

Process characteristics: Insert molding usually requires pre-placing the insert in the mold and then injecting resin for curing; while over-molding may involve multiple molding processes to improve external properties.

In Conclusion

Insert molding is an efficient and versatile manufacturing process with advantages including reduced costs, improved design flexibility and enhanced part reliability. Understanding the process flow, design points and applications of insert molding can help manufacturers better apply this technology in different industries. Whether it is used for prototyping or mass production, insert molding is an important method for manufacturing high-performance multi-material parts.

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