Axial Flux Motor Rotor Magnet Fixation Solutions: A Technical Overview From Adhesive Bonding To Mechanical Locking

Axial flux motors are becoming the “new power darling” in fields such as new energy vehicles, humanoid robots, and low-altitude aircraft—at the same power, they are 50% lighter and 50% smaller in axial dimension. But manufacturing this flat disc-type motor is far from as simple as “flattening a cylinder.” The magnets laid flat on the rotor disc withstand centrifugal force amplified many times over during high-speed rotation of tens of thousands of rpm. Once fixation fails, the magnets can fly out; at best the rotor is scrapped, at worst the stator is damaged. How to “lock” the magnets onto the rotor disc has become a key proposition for axial flux motors moving from the laboratory to mass production.

Why Magnet Fixation Is the “Achilles’ Heel” of Axial Flux Motors

The structure of axial flux motors determines that their fixation challenge is more severe than that of radial motors. In radial motors, magnets are embedded on the surface of a cylindrical rotor; centrifugal force is mainly radial outward and is naturally borne by the rotor core and sleeve. In axial flux motors, however, magnets are laid flat on the disc surface, and the force application points are near the outer diameter. At the same rotational speed, the linear speed at the edge of the rotor disc is much higher than that of a slender radial motor, so centrifugal force is multiplied. At the same time, during motor operation, the rotor’s magnetic components are also subjected to axial and radial electromagnetic forces, making displacement and detachment likely.

More troublesome is the thermal environment. Axial flux motors have a flat structure and narrow heat dissipation channels, so magnets must withstand high-temperature operating conditions above 150°C for long periods. In conventional radial motors, the commonly used adhesive bonding solution tends to fail due to epoxy resin aging above 120°C. High temperatures can also cause irreversible demagnetization of magnets, with performance degradation of more than 10%.

Centrifugal force, electromagnetic force, and high temperature—three pressures superimposed—make magnet fixation one of the most core technical challenges in Axial Flux Motor Rotor design.

Solution 1: Adhesive Bonding—Most Widely Used, but Not Omnipotent

Adhesive bonding is currently the most common magnet fixation method for axial flux motors, with epoxy structural adhesives as the mainstream. Single-component epoxy adhesives can withstand temperatures from -50°C to 210°C and have high shear strength and impact toughness. Mercedes-Benz’s YASA axial flux motor patent adopted this approach: multiple receiving portions are provided on the rotor disc; after the magnets are placed, they are fixed with adhesive; after the adhesive cures, it forms a mating structure with the rotor disc, connecting the rotor disc and magnets into an integrated structure.

However, the limitations of adhesive bonding are also obvious. First is the risk of high-temperature failure: above 120°C, the adhesive layer ages faster, creating a risk of detachment after long-term operation. Second is recycling difficulty: disassembly requires high-temperature heating, which is not conducive to material recycling. Third is low assembly efficiency: adhesive bonding requires waiting for curing, making it difficult to match the takt time of mass production.

In response to these shortcomings, the industry is improving in multiple directions. A first support plate is designed between the magnets and the rotor core, so that the magnets do not directly contact the core. This not only ensures space for the adhesive but also prevents the magnet coating from being damaged by friction during assembly. At the material level, PGH special magnets degrade by less than 3% in performance at high temperatures. Used with epoxy structural adhesives, the cost is about 32% lower than traditional solutions.

Solution 2: Mechanical Pressing and Locking—Using Structure to Counter Centrifugal Force

The core idea of mechanical fixation is: do not let the adhesive bear the load alone; instead, use physical structures to constrain the magnets from multiple directions. The axial flux motor patent publicly disclosed by Xiaomi Auto in 2026 shows a typical multiple-constraint design: the fixing component includes radial pressing pieces and an annular collar; the spoke pressing portions of the pressing pieces press against the sides of adjacent magnets, and the end clamping blocks engage with slots on the inner wall of the collar; the collar radially gathers and presses the pressing pieces and magnetic components while restricting radial play. The entire structure simultaneously constrains axial and radial displacement of the magnets and core. Even if the adhesive fails under high-temperature and high-speed conditions, it can still constrain the magnets and reduce the risk of flying out.

Nanchang Sanrui Intelligence’s patent adopts another approach: stainless steel pressure plates are placed between adjacent magnets in sequence; the two ends of the bottom of each pressure plate press against the protruding strips on both sides of the magnets, and then screws lock them tight. The key to this design is to use the downward pressure generated by the stainless steel pressure plates to directly press the magnets and prevent movement, while improving assembly efficiency.

MAGNAX’s patent solution goes further: locking features extending radially are provided on the front side of the back iron, located between adjacent magnets, to axially lock the magnets onto the back iron. The locking features can be V-shaped spring sheets, using elastic deformation to apply clamping force to the edges of the magnets. The advantage of this solution is that its characteristics do not depend on temperature like adhesives, offering higher reliability and durability.

The main cost of mechanical solutions is an increased number of parts, increased rotor weight, and cost pressure from high-precision machining. However, considering the reality that magnets account for 35%-40% of the total cost of axial flux motors, appropriately increasing investment in mechanical structures in the fixation step brings a significant improvement in full-lifecycle reliability.

Solution 3: Carbon Fiber Winding and Sleeves—the “Ultimate Defense Line” for High-Speed Scenarios

When rotational speed climbs to 18,000 rpm or even higher, adhesive bonding and mechanical pressing alone are no longer sufficient to ensure safety. High-end axial flux motors generally use carbon fiber winding as the last line of defense.

Carbon fiber prepreg is wound around the rotor periphery under a certain tension, wrapping the magnets as a whole to form a high-strength circumferential constraint layer. In its carbon fiber rotor patent, Tesla discloses that the carbon fiber sleeve thickness can be controlled within the range of 0.1-1.2 mm, minimizing sleeve thickness by causing the fibers to bear high pretension during winding. The winding process needs to be carried out at low temperature to compensate for the thermal expansion difference between carbon fiber and the metal rotor, or a large preload must be applied to ensure it does not loosen at low temperatures.

The process difficulty of carbon fiber winding lies in tension consistency. If the winding is loose or tight unevenly, dynamic balance cannot be stabilized; a slight vibration at high speed is a hidden danger. Therefore, high-end production lines generally are equipped with winding equipment that monitors pre-pressure in real time, adjusting carbon fiber tension and guide angle through linked control components to ensure pre-pressure remains within a reasonable range.

Outside the carbon fiber layer, some solutions also add a high-strength non-magnetic metal sleeve, forming a composite protection system of “carbon fiber winding + metal sleeve.” Another approach is to use an embedded disc-type rotor, in which the magnets are embedded inside the disc structure rather than on the surface, fundamentally changing the force pattern.

Solution 4: Potting and Injection Molding—the Mass-Production Path for Integrated Encapsulation

The potting solution injects liquid polymer material into the magnet receiving cavities of the rotor disc. After curing, it completely encapsulates and fixes the magnets within the disc body. This method can simultaneously achieve magnet fixation, insulation protection, and heat dissipation.

For axial flux motors, potting has an additional special significance—in dual-rotor solutions, the middle stator is flattened and has a small contact area with the outside, so heat dissipation almost entirely depends on potting adhesive. High-thermal-conductivity potting adhesives can achieve a thermal conductivity of 2-3, helping conduct stator heat out while fixing the magnets.

In the injection molding direction, by integrally encapsulating the rotor disc and magnets with injection molding material, the manufacturing process can be simplified and production efficiency improved. In Mercedes-Benz’s patent solution, after the adhesive material solidifies, it forms a mating structure with the rotor disc in the receiving portion, fixedly connecting the rotor disc and magnets into an integrated structure. BMW’s patent solution embeds the magnets in specially designed metal encapsulation bags and integrates an axial stop structure to prevent radial movement of the magnets. The air gap design on the metal encapsulation bags can reduce stray magnetic fields and optimize the flux path.

There Is No “Best” Solution, Only the “Most Suitable” Combination

In actual engineering, almost no product relies on a single solution. The practice truly adopted on mass-production lines is composite fixation: adhesive provides basic positioning and shear load bearing, mechanical pressing parts bear the main centrifugal force, and carbon fiber winding or sleeves serve as the final safety barrier. Some high-end solutions use a composite fixation method combining snap-fit mechanical locking and adhesive bonding, reducing dependence on a single adhesive layer.

Taking a motor operating at 18,000 rpm as an example, the mass-production line uses fully automated magnet assembly equipment, with segmented pole staggering, online polarity detection, and anti-collision mechanical structures, achieving a yield stable above 95%. After magnet installation, carbon fiber winding and dynamic balance weighting are performed before the entire rotor can enter final assembly.

Evolution Direction of Fixation Solutions

The choice of magnet fixation solution is essentially a multi-objective trade-off among centrifugal force, temperature, cost, and mass-production efficiency. As axial flux motors move from “handcrafted customization” to “assembly-line mass production,” the standardization of fixation solutions is rapidly increasing. Through self-developed special magnets and automated production lines, domestic solutions have reduced the additional cost proportion brought by exclusive processes such as high-precision dual-rotor assembly from more than 40% in the early stage to 22%.

In the coming years, as axial flux motors accelerate their deployment in scenarios such as new energy vehicles and humanoid robots, fixation solutions will diverge in two directions: “adhesive bonding + simple mechanical locking” for cost-sensitive applications, and composite solutions of “carbon fiber winding + multiple mechanical constraints + high-thermal-conductivity potting” for high-performance scenarios. Whichever route is taken, the core logic is the same—digest the invisible opponent of centrifugal force into the structural design in advance.