Feature article: PIM International, Vol.3 No. 3 September 2009, pages 41-50, 5754 words

Author: DI (FH) Dr. Branislav Zlatkov, Fotec GmbH, Austria

Fotec GmbH, Viktor Kaplan-Straße 2, 2700 Wiener Neustadt, Austria

The demand for high performance soft and hard magnets has seen massive growth over the last 20 years and the current push towards electric vehicles is set to further increase demand on both performance and shape complexity. PIM technology has an opportunity to further diversify into this potentially lucrative sector. In the following report for PIM International, Dr. Branislav Zlatkov presents an introduction to the use of magnetic materials and considers that challenges that exist for production via the PIM route.

Powder injection moulding (PIM) is an extremely flexible manufacturing technology that enables the production of generally small components to highly complex geometrical shapes from a wide variety of materials (metals, ceramics etc.). This is something that is often impossible, or at least uneconomical, when other shaping technologies are used [1-3]. Today, both soft and hard magnetic materials are used in the production of numerous components for various applications. Some complex magnetic parts are already made using PIM technology.

Introduction

In this review, modern magnetic materials and their properties are described in brief. Fundamentals and other details of PIM technology as related to magnetic materials are outlined, including equipment selection and tooling, magnetic powders and feedstock characterisation, alignment in the magnetic field, the magnetisation and demagnetisation of PIM sintered magnetic products, and the main properties of these products [4]. Special attention has been paid to analysing the application of PIM technology in the production of hard magnetic materials.

Magnetism is one of the oldest known physical phenomena. The first magnetic material found in rocks in ancient Greece was magnetite, i.e. iron oxide Fe3O4. The story is that a shepherd named Magnes noticed during a walk on a hill called Ida, situated on a rocky plane, the fact that pieces of mountain rock (magnetite) were attracted to his iron buckle. He then also noticed that two pieces of this rock attracted each other, and the history of magnetism started......

Further sections of this article include:

- Introduction
- ‘Easy to understand’ magnetism
    Remanence Br 
    Saturation (Hs and Bs)
    Coercivity Hcb 
    Permeability 
    Curie temperature Tc
- Magnetic anisotropy
- Magnetic materials
- The significance of PIM technology in magnet production 
    Powder preparation 
    Preparation of feedstock 
    Injection machine, injection tool concept, and power source 
    Injection moulding 
    Demagnetisation of green parts 
    Debinding 
    Sintering and optimisation 
    Thermal and thermomagnetic treatment 
    Additional treatments
- Conclusion
- Acknowledgments

Figures and Tables:

Fig. 1 A number of soft magnetic components have been produced by PIM for many years. This printer yoke is produced by Epson Atmix Corp., Japan

Fig. 2 Magnetic field and magnetic moment of hydrogen

Fig. 3 Hysteresis loops for anisotropic strontium hexaferrite (a) and MnZn ferrite (M-33 Siemens) (b) and demagnetisation curves (2nd quadrant) for anisotropic strontium hexaferrite (c) and MnZn ferrite (M33) (d)

Fig. 4 Summary: soft, semi hard and hard magnetic materials

Fig. 5 Pressed and sintered NdFeB permanent magnet cores (Courtesy TDK Corp., Japan)

Fig. 6 Examples of complex shapes of plastic bonded NdFeB

Fig. 7 Flow Diagram of PIM shaped hard magnetic materials

Fig. 8 Remanent induction Br (a), coercive force Hcb (b) and density ρ (c) vs. sintering temperature for isotropic (red) and anisotropic (blue) barium hexaferrite samples obtained by PIM technology; measured in direction parallel to the magnetic field applied during injection

Fig. 9 Microstructure (optical microscopy) of anisotropic barium hexaferrite PIM samples sintered at three differents temperature for the same sintering time of 1 h in air; magnification 200 x. The easy magnetisation axis is normal to the hexagonal planes e.g. normal to the picture surface

Fig. 10 X-ray diffraction patterns taken with CuKα radiation of sintered barium hexaferrite PIM samples: a) SIN-top surface, no magnetic alignment (isotropic), b) SAN-top surface, magnetic alignment (anisotropic)

Table 1 Most commonly used soft magnetic materials

Table 2 Basic properties of hard magnetic materials and their appearance