Injection-molded magnets are a unique composite material formed by blending magnetic material with plastic/nylon or rubber using injection molding techniques. The process involves molds, earning them the name “moldable magnets.”

This technology allows for a seamless fusion of magnets, plastic, and metal through injection molding, enabling the creation of diverse magnetic products with intricate shapes and versatile functionalities. Injection molding has emerged as a vital method for producing an extensive array of magnetic items.

These magnets find extensive use across automotive, electronics, medical devices, and consumer goods industries. They play essential roles in sensors, motors, actuators, and various other applications.

Due to the plasticity of plastic itself and the application of injection molding technology, injection molded magnets have a high degree of flexibility, which is mainly reflected in the following aspects:

In addition to the above characteristics, injection molded magnets also have the characteristics of high dimensional accuracy, low mass production cost, free combination with metal accessories, and no need for assembly of magnetic components. They are the perfect solution for magnetic components used in small motors and sensors.

• Special shapes and large quantities:

Injection molding technology can produce magnets of various complex shapes through molds. Therefore, when special shapes of magnets are required and the quantities are particularly large, injection molding is an ideal choice.

• Low magnetic requirements:

When magnetic requirements are not particularly high or general magnetic properties are required, injection molded magnets can provide adequate performance.

• Harsh environment applications:

If the product will be placed in an oxidizing or corrosive environment, injection molded magnets may be more suitable, because injection molding can use specific materials and processes to make the product more corrosion-resistant.

• Better impact resistance:

Due to the use of plastic materials, injection molded magnets may have better impact resistance, and are especially suitable for applications that require stronger toughness and durability.

Magnetic powders, including various types such as SmFeN, ferrite, NdFeB and SmCo, form the basis of injection molded magnets. These powders determine the magnetic properties of the final product. The magnetic powder filled in composite magnetic materials is mostly ferrite, such as BaO·6Fe2O3, SrO·6FeO, etc.

In comparison to traditional press-bonded NdFeB magnets, injection molded magnets boast high dimensional accuracy, simplified processes, low production costs, good anti-corrosion properties, and streamlined component molding. However, their magnetic properties tend to be relatively lower.

The maximum (BH) max of anisotropical injected ferrite can reach 2.2MGOe, while the isotropic injected bonded NdFeB can reach 6MGOe, and the isotropic press-bonded NdFeB can reach 11MGOe. Both are isotropically bonded magnets, but the performance of the injected magnets is nearly 5MGOe lower than the pressed magnets. Therefore, despite there are many obvious advantages of injection magnets, their use is still limited in many situations where high-performance magnets are required.

Anisotropic NdFeB powder, a high-performance material, exhibits over double the performance compared to isotropic NdFeB powder, containing the same neodymium rare earth element. Yet, its use at high temperatures is limited due to irreversible magnetic flux loss. In contrast, injected samarium cobalt powder offers lower flux loss, compensating for anisotropic NdFeB’s shortcomings. Therefore, combining these two high-performance magnetic powders can not only reduce the amount of rare earths and the irreversible loss of magnetic flux, but also greatly improve the magnetic properties.

Polymers are important matrix materials that bind magnetic powder together and can be used to make a variety of injection molded magnets. These materials make injection molded magnets different from sintered magnets and more flexible in product design. They can produce both hard and flexible magnetic products.

Domestic injection molded magnets commonly utilize nylon (PA) as a binder, particularly PA6 and PA12. PA6, despite its affordability, possesses high water absorption and susceptibility to deformation after water absorption, suitable for crafting magnets with standard precision. Conversely, PA12 exhibits superior strength, low water absorption, and less deformation after absorbing water, making it ideal for high-precision magnet production.

Demand in high-end markets, such as automotive industries, necessitates magnets with heightened temperature resistance, stability, and strength. Yet, nylon 6 and nylon 12 series in injection molded products face limitations in high-temperature resistance, restricting their use (with long-term working temperatures of only 150℃ and 120℃, respectively).

Polyphenylene Sulfide (PPS) emerges as a viable solution due to its impressive temperature resistance (operating between 200-250℃), low water absorption, and dimensional stability. However, the monopolization of PPS production by major corporations results in heightened costs, often making it unaffordable for many customers.

Manufacturers frequently undertake modifications to plastic raw materials. This process aims to enhance the binder’s high-temperature resistance and toughness, seeking to strike a balance between product performance and cost-effectiveness.

Additional additives or fillers can be added to change the specific properties of magnetic compounds, such as coupling agents, plasticizers, lubricants, heat stabilizers, antioxidants and epoxy resins, and other additives. Among them:

The function of the coupling agent is to coat the surface of the rare earth powder so that the magnetic powder and the binder can be better combined.

Plasticizers have the effect of softening the resin and can increase the processability of the powder mixture during the mixing process and the pellets during the forming process.

The function of the lubricant is to adjust the fluidity of the powder mixture during the mixing process and the pellet during the forming process to facilitate demolding.

Thermal stabilizer is one of the important additives for plastic processing. Its main function is to effectively prevent, reduce or even basically stop the degradation of materials during thermal processing and use.

Hardware usually refers to parts or components made of metal. During the manufacturing process of injection molded magnets, hardware can be used as support and fixation of reinforced materials to ensure the structural stability and functional integrity of the magnetic product. This hardware may include steel parts, screws, nuts, washers or other metal fittings that play a critical support role throughout the injection molding process.

What needs to be noted here is that if it is an over-molded or insert-molded magnetic product, the magnetic material used will be processed permanent magnets instead of magnetic powder.