Soft Magnetic Core Compaction and Rapid Heating for Nanocrystallization

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Solution Overview

Problem

Existing methods for producing soft magnetic cores face challenges in achieving high saturation polarization and low coercive field strength, particularly due to the absence of ferromagnetic alloying elements, rough surfaces leading to low fill factors, and limitations in heating rates, which affect power density and throughput in industrial applications.

Innovation Solution

A method involving simultaneous compaction and heat treatment of amorphous or semi-crystalline strips using mechanical compressive force, electric current heating, or inductive heating, with heating rates up to 1000 K/min, to form nanocrystalline grains, and applying insulation layers to prevent eddy currents, resulting in improved fill factors and magnetic properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If conventional furnace heat treatment is used, then the process is simple and equipment is available, but the heating rate is too low to form nanocrystalline grains

Engineering Contradiction:

Improveheating rateVSAvoidheat treatment equipment

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent replaces the conventional mechanical furnace heating system with an electromagnetic induction heating system. The induction heating device generates a time-varying magnetic field that induces eddy currents in the strip, producing heat directly within the material. This substitution enables heating rates of several Kelvin per second, which are necessary for nanocrystalline grain formation, while avoiding the need for complex conventional furnace systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent utilizes the phase transition from amorphous to nanocrystalline structure during heat treatment. By controlling the heating rate and temperature profile, the amorphous strip transforms into a nanocrystalline material with enhanced magnetic properties. The rapid heating enables controlled crystallization at specific temperatures, forming nanometer-sized grains within the amorphous matrix.

Inventive Principle:

Principle #36Phase transitions

2Manufacturing precision

If the strip surface is left rough, then the manufacturing process is simple, but the fill factor of toroidal cores is reduced to about 80%

Engineering Contradiction:

Improvesurface finishVSAvoidfill factor

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent applies a coating layer to the strip surface, changing the surface parameters. This coating reduces surface roughness and enables better packing of strips during toroidal core formation. The coated surface allows for increased fill factor by improving the contact and arrangement between adjacent strips, thereby increasing the volumetric efficiency of the magnetic core.

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If ferromagnetic alloying elements are added to increase saturation polarization, then magnetic performance improves, but grain growth is inhibited requiring shorter heat treatment duration

Engineering Contradiction:

Improveferromagnetic elementsVSAvoidheat treatment duration

Core Design Contradiction:

Quantity of substanceVSDuration of action of stationary object

Solution Approach 1:

The patent adds ferromagnetic alloying elements to the strip composition before heat treatment. These elements serve a dual function: they increase the saturation polarization to enhance magnetic performance, and they control grain growth during the subsequent heat treatment process. The preliminary addition of these elements prepares the material to achieve both high magnetic saturation and controlled crystallization within the required heat treatment duration.

Inventive Principle:

Principle #9Preliminary anti-action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The method enables the production of soft magnetic cores with enhanced magnetic saturation polarization, reduced coercive field strength, and increased fill factors, leading to higher power density and efficiency in industrial settings.

Implementation Method 1

an electric current flows through the amorphous or semi-crystalline strip, which is heated by the electric current flow

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

the amorphous or semi-crystalline strip can be heated by inductive heating while the compressive force is being exerted

Methodology Applied

Scientific EffectInductive heating: Induction Heating

Data Source

PatentEP4593040A1Method for producing soft magnetic core

Publication Date: 2025.07.30 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

Figure 1~2

AI summary

In a method for producing a soft magnetic core, at least one amorphous or semi-crystalline strip (3) made of a metallic alloy is wound around a winding axis, and the amorphous or semi-crystalline strip (3) is then introduced into a holding device (1). In addition, a pressing device (4) then exerts a mechanical compressive force on the wound amorphous or semi-crystalline strip (3), during which an electric current flows through the amorphous or semi-crystalline strip (3), which is heated by the electric current flow, and/or during which the amorphous or semi-crystalline strip (3) is heated by inductive heating, and/or during which the amorphous or semi-crystalline strip (3) is heated indirectly by means of a heating coil spaced apart from the amorphous or semi-crystalline strip (3), such that nanocrystalline grains are formed in the amorphous or semi-crystalline strip (3).