Axial flux and radial flux are two common motor architectures used in electric vehicles, industrial equipment, aerospace systems, and other high-performance applications.

The basic difference is the direction of the magnetic flux relative to the motor shaft. This difference affects motor geometry, torque density, thermal management, manufacturing, and the type of magnetic core material that can be used.

Main Points

Flux Direction: In a radial flux motor, magnetic flux travels primarily perpendicular to the rotation axis. In an axial flux motor, it travels primarily parallel to the rotation axis.
Motor Geometry: Radial flux motors typically have a longer cylindrical structure, while axial flux motors are generally shorter in the axial direction and wider in diameter.
Performance Trade-Off: Axial flux designs can achieve high torque and power density in a compact package, while radial flux motors benefit from mature manufacturing processes and a well-established supply chain.
Core Material Selection: Radial flux motors commonly use stacked non-grain-oriented electrical steel laminations. Axial flux motors can use electrical steel, wound or segmented cores, and soft magnetic composites depending on the core design and magnetic path.

How Flux Direction Affects Motor Geometry

Radial and axial flux motor geometry showing cylindrical and disc-shaped rotor and stator configurations

Radial vs Axial Flux Motor Geometry

Radial Flux: The Typical Circular Form

Radial flux motors are widely used in automotive and industrial applications and typically have a cylindrical form. Inside, a central rotor spins within a larger, hollow stator.

Axial Flux: The Small-Size "Pancake" Shape

An axial flux motor uses one or more disc-shaped rotors arranged parallel to the stator. This gives the motor a short axial length and relatively large diameter, which can be useful where installation length is limited, such as compact EV powertrains and some in-wheel motor designs.

Feature	Radial Flux Motor	Axial Flux Motor
Shape	Long and cylindrical	Short and disc-shaped ("pancake")
Path of Flux	Perpendicular to rotation axis	Parallel to rotation axis
Stator/Rotor	Nested cylinders	Disc planes
Advantages	Mature manufacturing	High torque density, compact axial packaging

The Impact on Performance: Efficiency, Torque, and Manufacturing

Efficiency and Torque Density

Axial flux motors are attractive where high torque density is required within limited axial space. Their relatively large effective air-gap radius allows torque to be produced over a broad disc-shaped area, although actual torque density still depends on motor diameter, magnetic loading, current density, cooling, and other design parameters.

Well-optimized axial flux motors can also achieve high efficiency. Efficiency likewise depends on the complete electromagnetic, thermal, and mechanical design rather than motor topology alone.

Heat Management

In many radial flux designs, the windings are located within the stator structure, which can create a longer thermal path to the housing.

Some axial flux architectures can offer advantages in thermal management. Their flatter geometry can place windings closer to the housing or cooling structure, shortening the thermal path from the windings to the cooling system.

Manufacturing and Scale

Radial flux motors benefit from decades of manufacturing development. Lamination stamping, stacking, winding, rotor assembly, and automated production processes are already widely established.

Axial flux motors introduce a different set of manufacturing challenges. Disc alignment, air-gap control, segmented stators, winding configuration, and magnetic forces can require specialized production methods. Maintaining a uniform air gap across a large disc diameter is especially important because small deviations can affect electromagnetic performance and mechanical stability.

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Close-up of HWHG thin-gauge electrical steel showing surface quality, flatness, and precise strip geometry

Upstream material consistency is also important, particularly for thin electrical steel used in motor laminations. HWHG was the first manufacturer globally to apply an 18-high six-stand tandem mill to high-end electrical steel production. The process supports thin-gauge rolling with tighter shape control and higher production efficiency.

Core Material Selection for Axial and Radial Flux Motors

Non-Grain-Oriented Electrical Steel (NGOES)

Non-grain-oriented electrical steel (NGOES) is widely used in motor stators and rotors because its magnetic properties are relatively uniform in different directions within the sheet plane. In conventional radial flux motors, NGOES sheets are typically stamped into laminations and stacked to form the motor core. This laminated structure helps guide the magnetic flux while limiting eddy-current losses.

Electrical steel can also be used in axial flux motors, although the core geometry may require different manufacturing approaches, such as tape-wound or segmented cores. In some axial flux designs where the magnetic flux follows a more clearly defined direction, grain-oriented electrical steel (GOES) may also be considered. Its magnetic properties are strongest along the rolling direction, so aligning the material with the intended flux path can help reduce core losses in suitable motor topologies.

Soft Magnetic Composites (SMC): Supporting Complex 3D Flux Paths

SMCs are particularly useful where the motor requires complex three-dimensional magnetic paths or core geometries that are difficult to manufacture from stacked laminations. Their high electrical resistivity can also help limit eddy-current losses.

However, SMCs generally involve trade-offs in permeability, saturation flux density, mechanical properties, and loss characteristics compared with laminated electrical steel.

Amorphous Materials: A Low-Loss Option for High-Frequency Motors

Amorphous magnetic alloys are produced as very thin metallic ribbons and are known for low core losses, particularly at higher electrical frequencies. This makes them attractive for motor designs where reducing iron loss is a major engineering objective.

Manufacturing remains more demanding than with conventional electrical steel laminations. Amorphous ribbon is thin and relatively difficult to stamp, stack, join, and form into complex motor-core geometries.

These manufacturing constraints make repeatable automotive-scale production a key challenge. HWHG has commercialized automotive-grade amorphous composite materials for electric-drive applications and has begun volume deliveries, providing a practical example of amorphous materials moving from motor research into production use.

HWHG Amorphous Alloy Production Line

HWHG amorphous ribbon production line for automotive electric-drive magnetic material applications

Material	Typical Strength	Key Limitation	Common Design Consideration
NGO Electrical Steel	High permeability, established lamination process, balanced magnetic performance	Lamination geometry can limit complex 3D flux paths	Widely used in conventional radial-flux motors and applicable to selected axial-flux core designs
GO Electrical Steel	Very good magnetic properties along the rolling direction	Strong directional dependence	Useful where the magnetic path can be aligned with the rolling direction
Soft Magnetic Composites	3D magnetic isotropy and flexible molded geometry	Lower permeability and saturation characteristics than many laminated steels	Useful for complex axial-flux stator geometries
Amorphous Alloy	Very low core loss, particularly at higher frequencies	Difficult core fabrication and handling	Considered where reducing iron loss is a priority

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Motor core material comparison with electrical steel laminations, soft magnetic composites, and amorphous ribbon

Why Core Loss Matters at Higher Electrical Frequencies

Motor core losses increase as electrical frequency rises. Eddy-current loss is strongly influenced by lamination thickness and electrical resistivity, while hysteresis loss depends on the magnetic properties of the core material. This is why thinner electrical steel, SMCs, and amorphous alloys become more relevant in high-speed or high-frequency motor designs.

Conclusion: A Connected Future of Design and Materials

The appropriate choice depends on flux direction, operating frequency, core geometry, loss targets, manufacturing method, and production requirements. These factors determine whether NGOES, GOES, soft magnetic composites, amorphous alloys, or a combination of materials is the better fit for a specific motor design.

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