The performance of the core drive unit – the Brushless DC (BLDC) motor – is crucial for fans, particularly high-efficiency fans used in heat dissipation and ventilation applications. Injection molded magnets have become an ideal choice for manufacturing the rotors of these motors due to their unique comprehensive advantages.

Core Advantages:

• High Efficiency & Lightweight: Injection molded magnets allow for the design of complex multi-pole magnetic circuits, optimizing magnetic field distribution and improving motor efficiency. Their relatively low density contributes to rotor lightweighting, reducing starting inertia.

• Excellent Dynamic Balance & Low Noise: The high consistency of injection molding ensures superior initial dynamic balance of the rotor, significantly reducing vibration and noise during high-speed operation, meeting the quietness requirements of fans.

• High Structural Strength & Safety: Engineering plastic binders provide the magnets with good toughness, effectively resisting centrifugal forces generated by high-speed rotation, preventing magnet fracture, and enhancing motor reliability.

• Integrated Molding of Complex Structures: Enables one-time overmolding of the magnet around the shaft, simplifying the assembly process and achieving good concentricity.

Core Manufacturing Process Flow:

1. Raw Material Preparation & Mixing

   • Magnetic Powder: Neodymium Iron Boron (NdFeB) magnetic powder is primarily used to achieve high magnetic energy product and coercivity, ensuring high power density and efficiency for the motor. Strontium ferrite (Sr-Ferrite) can also be used in cost-sensitive applications.

   • Binder: Commonly used binders include Nylon (PA66, PA12) or Polyphenylene sulfide (PPS). PA materials offer good toughness and cost advantages; PPS provides higher heat resistance and dimensional stability.

   • Mixing & Pelletizing: Magnetic powder, binder, and additives are uniformly mixed, then melted, extruded, and pelletized via a twin-screw extruder to produce high-performance magnetic compound pellets.

2. Precision Injection Molding

   • Insert Treatment: The motor shaft, acting as an insert, requires preheating and surface cleaning to enhance the bond between the plastic and metal.

   • Injection Molding Process: Magnetic pellets are injected into the mold cavity containing the shaft using specialized injection molding machines. Parameters like temperature, pressure, and speed are precisely controlled to ensure complete mold filling, minimal internal defects, and a strong bond with the shaft. The design of the mold's gate and cooling system critically impacts product quality.

3. Magnetization

   • The molded rotor undergoes multi-pole magnetization (e.g., 8-pole, 12-pole). The precision of the magnetization fixture and the stability of the magnetization equipment directly determine the accuracy of magnetic pole positioning and the uniformity of magnetic field strength, thereby affecting the motor's torque smoothness and noise levels.

4. Performance Testing & Correction

   • Dynamic Balance Correction: This is a core inspection step for fan rotors. Testing must be performed on a dynamic balancing machine, and unbalance is corrected to within standards (e.g., G6.3 grade) through methods like material removal or laser correction. This is essential for ensuring smooth and quiet fan operation.

   • Magnetic Performance Testing: Specialized instruments are used to check surface magnetic field strength and waveform.

Process Challenges & Requirements:

• High-Speed Reliability: Requires extremely high bond strength between the injection molded magnet and the metal insert to withstand continuous centrifugal forces.

• Balancing Cost & Performance: Controlling costs through material selection and process optimization while meeting performance requirements is crucial.

• Temperature Resistance: Continuous motor operation generates heat, requiring the magnet material to withstand operating temperatures without demagnetization.

Summary

The injection molded magnet process provides high efficiency and reliability for manufacturing high-performance fan motors. This field requires suppliers to have solid experience in material formulation, precision mold making, process control, and dynamic balance correction. Companies like Ningbo Buji Magnetic-Electronic Technology Co., Ltd., leveraging their extensive product line of injection molded magnets (e.g., PPS and PA bonded NdFeB/Ferrite magnets) and industry experience, are capable of providing fan motor customers with rotor magnet solutions that meet their requirements.