Laminated Magnets

What Are Laminated Magnets?

Laminated magnets are permanent magnets made from multiple thin magnetic layers bonded together with insulating layers in between.

This type of design is mainly used for rare earth magnets in applications where the magnets are exposed to time-varying magnetic fields during operation.

Unlike a conventional solid magnet, a laminated magnet uses an internal layered arrangement to divide the conductive magnet body into thinner sections. These sections are electrically separated from one another by thin insulating materials, while still forming a complete magnet part after bonding.

In practical projects, laminated magnets are often made in arc or other segmented forms to fit motor rotor structures and related assembly designs.

Why Are Laminated Magnets Used in High-Speed Motor Projects?

In high-speed motor projects, rare earth magnets may be exposed to time-varying magnetic fields during operation. Because these magnets are electrically conductive, eddy currents can be induced inside the magnet body. As the rotational speed and field variation increase, the resulting eddy current loss can become more significant, leading to additional heat generation in the rotor and increasing the risk of temperature rise, efficiency loss, and magnetic performance degradation.

This issue is especially important for rare earth magnets because they offer high magnetic output, but their electrical resistivity is not high enough to naturally suppress internal eddy currents under demanding operating conditions.

In comparison, bonded magnets have much higher resistivity and are therefore less affected by this problem, but they are often limited in magnetic performance and temperature capability. For this reason, laminated magnets are used as a practical solution in some high-speed motor designs where both strong magnetic output and better control of rotor loss are required.

Eddy Current Loss Density Distribution in the Laminated Magnets

Source: JSOL Corporation

By dividing one magnet into multiple thinner pieces and placing insulating layers between them, the current path inside the magnet can be interrupted effectively. This helps reduce the circulating current within the conductive magnet body, thereby lowering eddy current loss and improving the thermal behavior of the rotor. That is why laminated magnets are often considered in motor projects where speed, temperature rise, and operating reliability need to be evaluated together.

Common Forms of Laminated Magnets

In practical motor projects, laminated magnets are often made as arc segments for rotor assembly. This form is especially common in high-speed motor designs, where rotor layout, pole number, and assembly method all need to be considered together.

In some cases, laminated magnets may also be made in block form or other segmented shapes, depending on rotor configuration and overall design requirements. Compared with one-piece magnets, laminated magnets in these forms offer greater flexibility in balancing magnetic performance, eddy current control, machining feasibility, and assembly needs.

For this reason, the forms of laminated magnets are usually defined together with rotor design rather than treated as standard magnet shapes alone. Factors such as magnetization direction, segment geometry, working surface, bonding method, and final assembly accuracy can all affect which forms of laminated magnets are more suitable for the project.

Key Design Considerations for Laminated Magnet Projects

For laminated magnet projects, the design work usually involves more than simply dividing one magnet into several thinner layers. In most cases, factors such as magnet grade, layer thickness, insulation thickness, magnetization direction, segment geometry, and rotor operating conditions all need to be considered together. These factors can directly affect not only the eddy current reduction effect, but also the final magnetic output, dimensional control, and manufacturing feasibility of the laminated magnet.

Among these points, the thickness of each magnetic layer and the consistency of the insulating layer are especially important. If the magnetic pieces are too thick, the reduction of eddy current loss may be limited. If the insulating layer is not controlled well, it can influence bonding quality, dimensional accuracy, and the consistency of the final assembled part. In practical production, the interlayer usually needs to remain thin and uniform, so the laminated magnet can still meet the required size while maintaining stable bonding performance.

It is also important to note that increasing the number of layers is not always the best solution. Although more layers can help reduce internal current paths further, the project must still be evaluated in terms of magnet size, processing difficulty, material utilization, bonding reliability, and the final assembly requirements of the rotor. For this reason, the lamination plan is usually determined as part of the overall motor project, rather than as an isolated magnet design decision.

Manufacturing Challenges of Laminated Magnets

Compared with conventional solid magnets, laminated magnets usually involve a more demanding manufacturing process. Each magnetic layer must be prepared with suitable dimensional consistency, while the insulating layer between the pieces needs to remain thin and uniform throughout the bonding process. This affects not only the electrical separation between layers, but also the dimensional stability and overall quality of the final laminated part.

In practical production, the main challenge is to balance eddy current reduction with manufacturing feasibility. As the number of layers increases, the process becomes more sensitive in terms of layer handling, bonding consistency, effective magnet size, material utilization, and final geometry control. For this reason, laminated magnets are usually more suitable for projects with clearer technical targets, where the lamination plan can be evaluated together with the actual motor design and assembly requirements.

Work with SDM on Laminated Magnet Projects

SDM can support selected laminated magnet projects based on customer drawings and actual motor design requirements. Depending on the project, this may include magnet material selection, lamination evaluation, prototype support, and related machining or assembly coordination.

Since laminated magnets are usually developed for more specific operating conditions, earlier communication is often helpful in clarifying factors such as magnet form, layer arrangement, rotor structure, and project feasibility. If you have drawings or defined technical targets, you are welcome to share them with us for review.