This contribution gives an overview of the production of permanently excited rotor assemblies
and possible faults in this process chain. In addition possibilities for error detection are
described and the compensation of these imperfections by selective magnet assembly is
illuminated. The focus of the work is on the reduction of the cogging torque using low-cost
magnets. In addition to the controllability of servo drives the cogging torque is particularly
responsible for the vibrations caused by an electrical machine. There are dependencies on the
one hand on the motor configuration and on the other hand on the angular deviation of the
magnetic moment vector of the individual magnets. Especially in permanently excited synchronous
machines with ironless Halbach rotors field distortions cannot be compensated by the rotor
iron as is the case with embedded magnets for example. This is also confirmed by the
measurements carried out within the scope of this work. The selective magnet assembly makes it
possible to raise an enormous cost saving potential by using cheaper magnets with minimised
cogging torque. This is achieved by compensating for the angular deviations of the individual
magnets from each other. For this purpose a compensated set of magnets is formed by
calculation algorithms. The implementation in a production environment is illustrated with the
help of a storage system that can fully automatically measure sort store and provide magnets
as a compensated magnet set. A concept demonstrator of such a storage system is presented the
cycle times are determined and optimisation potentials are identified. Based on an example
scenario in which a modular motor design with different variants and a medium annual total
number of units is to be manufactured with the help of selective magnet assembly the savings
potential through cheaper magnets is demonstrated. In the example the material costs for
high-quality magnets account for 25 % of the total manufacturing costs for a motor. In contrast
the material costs for the magnets are 70 % lower and the additional costs for a fully
automatic storage system are 1.5 % thus demonstrating the profitability of the strategy.
