Permanent Magnet Fracturing and Joining for IPM Motors

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Solution Overview

Problem

Existing methods for manufacturing permanent magnets for IPM motors, such as machining, lead to increased manufacturing costs, thermal demagnetization, and a decrease in magnetic properties due to eddy currents and irreversible thermal demagnetization, especially when increasing rotation speed or pole number.

Innovation Solution

A method involving pressure forming magnetic particles into a forming die, fracturing the sintered body into separate pieces along grain boundaries to maintain magnetic flux density and coercive force, and restoring the magnet by fitting fracture surfaces together, without the need for expensive cutting tools.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If the permanent magnet is machined into separate pieces using cutting tools, then the eddy current generation is suppressed, but the manufacturing cost increases and the main phases are cut reducing residual magnetic flux density

Engineering Contradiction:

Improveeddy current generationVSAvoidmanufacturing cost

Core Design Contradiction:

Object-generated harmful factorsVSEase of manufacture

Solution Approach 1:

The permanent magnet is divided into multiple separate pieces that are inserted into the rotor slot. This segmentation suppresses eddy current generation by interrupting the continuous magnetic path, while the pieces are subsequently joined together to form the complete magnet structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of cutting the sintered magnet body (which damages the magnetic structure), the invention forms the magnet from separate green compact pieces before sintering. The pieces are joined by friction stir welding after sintering, reversing the conventional sequence of cutting after sintering.

Inventive Principle:

Principle #13The other way round (Inversion)

2Object-generated harmful factors

If the permanent magnet is machined into separate pieces, then eddy current is suppressed, but expensive cutting tools with diamond chips are required and tool replacement frequency increases

Engineering Contradiction:

Improveeddy current generationVSAvoidcutting tool complexity

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The magnet is segmented into multiple pieces that are formed separately as green compacts, avoiding the need for complex cutting tools. The segmentation is achieved during the forming stage rather than through post-sintering machining.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The mechanical cutting process using diamond-tipped tools is replaced with friction stir welding technology. The joining process uses a friction stir tool that mechanically bonds the sintered pieces together without requiring expensive diamond cutting tools.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-generated harmful factors

If the permanent magnet is cut into separate pieces, then eddy current is reduced, but the grain boundary phase covering is broken exposing main phases to magnetic reversal

Engineering Contradiction:

Improveeddy current generationVSAvoidcoercive force

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The magnet pieces are formed as separate green compacts before sintering, with the grain boundary phase already present and intact. This preliminary formation prevents the need for post-sintering cutting that would expose main phases to magnetic reversal.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The conventional sequence of sintering then cutting is inverted to forming green compacts, sintering, then joining. This reversal ensures the grain boundary phase remains intact throughout the process, protecting the main phases from exposure.

Inventive Principle:

Principle #13The other way round (Inversion)

4Power

If rotation speed or pole number is increased to improve motor output performance, then motor performance improves, but eddy current generation increases causing thermal demagnetization

Engineering Contradiction:

Improvemotor output performanceVSAvoideddy current generation

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

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

This method reduces manufacturing costs, maintains high magnetic properties, and prevents thermal demagnetization, enabling the production of permanent magnets with superior performance for IPM motors.

Implementation Method 1

pressure forming magnetic particles for a permanent magnet in a forming die

Methodology Applied

Scientific EffectPressure forming: Compression

Implementation Method 2

forming two or more separate pieces by fracturing the permanent magnet

Methodology Applied

Scientific EffectFracture along grain boundaries: Fracture Mechanics

Implementation Method 3

restoring the permanent magnet by fitting fracture surfaces of adjacent separate pieces together

Methodology Applied

Scientific EffectFriction stir welding: Friction Welding

Data Source

PatentUS8497613B2Permanent magnet, manufacturing method thereof, and rotor and IPM motor

Publication Date: 2013.07.30 TOYOTA JIDOSHA KK

AI summary

A manufacturing method for a permanent magnet includes the steps of a) producing a permanent magnet (1), b) fracturing the permanent magnet (1) to obtain two or more separate pieces (13), and c) restoring the permanent magnet (1) by fitting the fracture surfaces of adjacent separate pieces (13) together.