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Magnet motor assembling

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Permanent-magnet rotors

Over the last 10 years, motors with permanent-magnet rotors have become widespread all over the world in a large variety of applications. Starting from the simplest and easiest domestic applications, to automotive, up to traction applications.


The structure of a motor with permanent-magnet rotor is similar to the one of synchronous motor where the rotor winding is replaced by permanent magnets to generate the magnetic excitation field.

Permanent magnet rotor

In the stator you can find phase-windings while on the rotor you can find magnets, which can be:

  • Applied on the outer surface of the rotor (Surface Permanent Magnets – SPM)

  • Inserted in the lamination stacks of the rotor (Internal Permanent Magnets – IPM)

There are two big families of brushless motors depending on the stator windings arrangement:



Permanent magnets can be manufactured mainly with ferrite or by using rare earth metals:

  • Permanent magnets made of ferrite are characterized by low residual inductions and high fragility levels with consequential difficult machining. Still these magnets are pretty widespread thanks to high coercitivity values compared to their low price.

  • The most common permanent magnets made of rare earth metals are manufactured with Neodymium, Iron and Boron. These magnets are characterized by a good quality/price rate while Cobalt ones are more expensive because of international market trends.

Generally speaking, magnets made of rare earth metals are more expensive than magnets made of ferrite, but they have higher energy ratings than ferrite ones and so they are used in more advanced technological solutions, where the price is not a key factor.

Magnets can be covered in surface films aimed at improving the performance. In industrial automation this feature is often underestimated and because of this the film can be damaged during handling, compromising the quality of the product.

Strengths and weaknesses


  • High reliability

  • High power factor

  • Absence of commutator-brushes system and its necessary maintenance

  • Higher speed and acceleration

  • Lower inertia, lighter weight, smaller size

  • Cooling systems simplification

  • Less inductance


  • The cost of magnets as well as the cost of the control electronics, leading to a high price of the final product (lessening over time though)

  • Criticalities in the motor manufacturing process implying various manual assembling phases

The motor manufacturing process implies the following criticalities to be faced:

  • Identification of appropriate solutions for fixing magnets to the rotor, always guaranteeing the required mechanical grip

  • Difficult manipulation of pre-magnetized magnets with consequential health & safety risks for the operators

In order to face these criticalities, it is advisable to work with a reliable partner operating in process automation and to cooperate on the definition of the most suitable production process.


RIMAC has 40-years’ experience in the field of electric motors and industrial automation: thanks to this expertise RIMAC can assist its customers in the process definition.

RIMAC has always been operating on the national and international stage and in recent years, the company has been cooperating with both leading permanent-magnet motors manufacturers and small, dynamic Italian organizations.

The know-how acquired over the years, led RIMAC team to develop a deep understanding of those solutions which can be implemented during the whole magnet-assembling process, such as the choice of the gluing adhesive:

There are many different solutions on the global market! That’s why RIMAC expertise is key to help the Customer to choose the best bonding solution for his products.

RIMAC is able to handle different types of glue made by the leading adhesives manufacturers such as Loctite ®, Delo ®, Permabond ® and Threebond ®.

Thanks to the close cooperation developed with a leading Italian company operating in the field, Laboratorio Elettrofisico ®, RIMAC can assist the customer in finding the best solution for magnetizing.

Laboratorio Elettrofisico ® magnetizing system
The starting point can be either the use of magnetized magnets or a post-assembly magnetization of the rotor. Between these two extremes, there are multiple solutions meeting the specific requirements expressed by the customer.

Working with RIMAC on this industrial automation project allows you to:

  • Industrialize the process

  • Reduce the manufacturing costs

  • Increase the productivity

  • Increase the quality standards of the product

  • Minimize human failure

  • Guarantee the highest manufacturing repeatability

  • Optimize the working area

  • Protect operators from health and safety risks (ex. Exposition to chemical agents and mechanical risks)