Magnetics Business & Technology - Summer 2012 - (Page 20)

FEATURE ARTICLE Article continued from pAge 8 ther define the time of the electrical current maximum or take the time of a spatially averaged field maximum. A more refined approach is to use the local times of the field maxima independently, (to calculate the resulting material parameters at different times for each single finite element). Generally these approaches do not take into account rotations of magnetization, especially when the pulse decays again. Such effects may lead to errors in predicted field components of the final magnet of around 10 percent, sometimes even higher. Consequently, taking into account that rotations of magnetization would require the use of vector hysteresis models such as the Vector Preisach model that approximates both the respective J(H) relations as well as rotations [4]. Similar models are still not able to supply unique and reality mirroring results for all sorts of hard magnetic materials. Additionally, they are not viable under normal industrial conditions. Background is the huge demand of computer resources and their big time consumption. More practical approaches are needed to take into account rotations of magnetization. One of such approaches is to approximate those rotations at one or two times of the decaying part of the pulse only. The vector sum of polarization remains constant on the level determined by the pulse maximum and rotations are estimated by mathematical models such as the Stoner-Wohlfahrt model [5]. Both basic methods of calculating parameter distributions in injection molded magnets sometimes need to be combined, e.g. when pole oriented anisotropic rare earth magnets are manufactured. In this case, the analysis of the mold, calculates the distribution of the direction of anisotropy. The treatment of the pulse magnetization is then performed within another step. Here the magnetizing field strength is projected onto the direction of anisotropy, which may also vary from finite element to finite element. References [1] T. Schliesch, B. Hagemann, H. Hartnuss, F. Poehlau, Plastic bonded anisotropic rotor with three different field areas for brushless DC motors, Sixth International Symposium on Electric and Magnetic Fields EMF 2003, Aachen, Germany, 2003 [2] T. Schliesch, Computations of parameter distributions in anisotropic bonded magnets with ANSYS®-EMAG, 16. CADFEM Users‘ Meeting, Bad Neuenahr, Germany, 1998, in German [3] N.Nakata, N. Takahashi, Numerical Analysis of Transient Magnetic Field in a Capacitor-Discharge Impulse Magnetizer, IEEE Transactions on Magnetics, Vol.22, No.5, p.526, 1986 [4] E. Della Torre, Magnetic Hysteresis, IEEE Press, New York, 1999 [5] E.C. Stoner and E.P. Wohlfahrt. “A mechanism of magnetic hysteresis in heterogeneous alloys“, Phil. Trans. Roy. Soc., vol. A240, pp. 599-642, 1948 Thomas Schliesch is Head of Research & Development at Max Baermann GmbH, which is a well known manufacturer of bonded magnets in Germany. Thomas graduated in Physics from university of Hamburg and joined the Max Baermann GmbH in 1989. A major part of his work he devoted to electromagnetic design and the development of specific methods for bonded permanent magnets. He can be reached at t.schliesch@max-baermann.de. 20 Magnetics Business & Technology • Summer 2012 www.MagneticsMagazine.com http://www.infowebcom.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Summer 2012

Magnetics Business & Technology - Summer 2012
Editor's Choice
Injection Molded Magnets for Electrical Machines
The Process of Developing and Testing a New Transformer
Rare Earths & Corporate Social Responsibility
Research & Development
RE-use, RE-duce, RE-cycle, RE-place
Magnets • Materials • Measurement
Application • Component Developments
Industry News
Rare Earth Crisis Dissected: Securing the Future
Marketplace
Advertising Index
Spontaneous Thoughts: The End of Axial Pressing?

Magnetics Business & Technology - Summer 2012