Powder Magnetic Core Flatness via Two-Step Heat Treatment
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Solution Overview
Problem
The challenge is to manufacture a powder magnetic core with improved flatness, as existing methods can cause surface bulging due to air expansion during heat treatment, leading to compromised flatness and potential rupture due to internal pressure.
Innovation Solution
A two-step heat treatment process is employed, where the first heat treatment occurs within the lubricant's melting point range to remove air and form channels, followed by a second treatment at a higher temperature to remove distortion, ensuring minimal air expansion and maintaining compact integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the temperature of the compact containing soft magnetic powder and lubricant is linearly increased to a relatively high temperature, then the air contained in the compact suddenly expands, but this causes a surface of the compact to bulge and deteriorate the flatness of the heat-treated body
Solution Approach 1:
The heat treatment process is divided into three distinct stages: first heat treatment (temperature rising stage) to remove air, second heat treatment (distortion removing stage) to eliminate internal stress, and optional third heat treatment (decomposition stage) to remove lubricant residues. This segmentation prevents sudden air expansion by progressively removing air before high-temperature heating, thereby maintaining compact flatness throughout the process.
Solution Approach 2:
Air removal is performed as a preliminary action before the main high-temperature heat treatment. The first heat treatment at controlled temperature removes air from the compact through melting and evaporation of lubricant, creating channels for air escape. This preliminary air removal prevents subsequent bulging and flatness deterioration during the distortion-removing heat treatment stage.
2Manufacturing precision
If heat treatment is performed to remove distortion, then the temperature must be increased to 400-900°C, but this high temperature causes air in the compact to expand and rupture the compact
Solution Approach 1:
Air removal is performed as a preliminary action before the main high-temperature heat treatment. The first heat treatment at controlled temperature removes air from the compact through melting and evaporation of lubricant, creating channels for air escape. This preliminary air removal prevents subsequent bulging and flatness deterioration during the distortion-removing heat treatment stage.
Solution Approach 2:
The process utilizes phase transitions of the lubricant (melting and evaporation) to facilitate air removal. During the first heat treatment, the lubricant melts and evaporates, creating channels that allow trapped air to escape from the compact. This phase transition mechanism enables safe removal of air before high-temperature distortion-removing heat treatment, preventing compact rupture.
3Manufacturing precision
If the compact is heated at high temperature to remove distortion, then manufacturing precision is improved, but the air expansion creates internal pressure that may rupture the compact
Solution Approach 1:
The heat treatment process is divided into three distinct stages: first heat treatment (temperature rising stage) to remove air, second heat treatment (distortion removing stage) to eliminate internal stress, and optional third heat treatment (decomposition stage) to remove lubricant residues. This segmentation prevents sudden air expansion by progressively removing air before high-temperature heating, thereby maintaining compact flatness throughout the process.
Solution Approach 2:
The lubricant, which could potentially cause harm through carbonization and adhesion, is utilized beneficially during the first heat treatment stage. By heating to the melting point of the lubricant, the process transforms the lubricant into a medium that facilitates air removal through melting and evaporation, creating escape channels that prevent harmful pressure buildup during subsequent high-temperature treatment.
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 results in a powder magnetic core with excellent flatness and reduced risk of rupture, achieving a surface flatness of 0.03 mm or less, while maintaining the strength of the compact.
Implementation Method 1
a first heat treatment step of performing heat treatment in a temperature range in which the lubricant melts
Implementation Method 2
a second heat treatment step of performing heat treatment in a temperature range in which distortion can be removed
Data Source
AI summary
A method for manufacturing a powder magnetic core, including a step of compacting a raw material powder to form a compact, a step of performing a first heat treatment on the compact to obtain a first heat-treated body, and a step of performing a second heat treatment on the first heat-treated body to obtain a second heat-treated body, wherein the raw material powder contains a soft magnetic powder and a lubricant that has a melting point Tm, the first heat treatment is performed in a temperature range from Tm to Tm+50° C. inclusive for a time longer than 10 minutes, and the second heat treatment is performed in a temperature range from 400° C. to 900° C. inclusive for a time of 3 minutes to 90 minutes inclusive, the temperature range of the second heat treatment being higher than the temperature range of the first heat treatment.