Sintered Compact Manufacturing via Dual-Stage Heating
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Solution Overview
Problem
The existing manufacturing methods for rare earth magnets face challenges in maintaining magnetic characteristics at high temperatures due to coarsening of crystal particles during hot press forming, particularly when using nanosized magnetic powders, leading to deterioration of magnetic properties.
Innovation Solution
A manufacturing method involving a forming mold with both preliminary and main heating parts, where the magnetic powder is initially heated to a lower temperature than the coarse crystal particle generation temperature, followed by main heating at a temperature below the generation temperature but above the preliminary heating temperature, ensuring uniform temperature distribution and preventing coarsening during press forming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If magnetic powder is rapidly heated from outside to densify the powder in a short period of time, then densification speed is improved, but temperature difference between inner region and outer region increases causing coarse crystal particle generation
Solution Approach 1:
The outer peripheral region of the magnetic powder is preliminarily heated before the main heating phase. This preliminary action reduces the temperature difference between inner and outer regions during subsequent densification, preventing coarse crystal particle generation while maintaining fast densification speed. The forming mold includes a heating coil that specifically targets the outer peripheral region for this preliminary heating action.
Solution Approach 2:
Different regions of the magnetic powder receive different heating treatments: the outer peripheral region receives preliminary heating at a lower temperature, while the inner region receives main heating at a higher temperature. This local differentiation of heating quality ensures uniform temperature distribution and prevents coarse crystal particle generation throughout the entire powder mass.
2Manufacturing precision
If magnetic powder is preliminarily heated in a muffle furnace then moved to a heating press, then particle coarsening is prevented, but temperature of the magnetic powder decreases between steps
Solution Approach 1:
The preliminary heating function and main heating function are merged into a single forming mold structure. The heating coil integrated into the forming mold performs preliminary heating of the outer peripheral region, eliminating the need to transfer the magnetic powder between separate heating devices. This integration prevents temperature loss and reduces processing time while maintaining crystal particle size control.
3Manufacturing precision
If nanosized magnetic powder is used to achieve miniaturization, then magnetic characteristics are improved, but coarsening of crystal particles during hot press forming deteriorates magnetic properties
Solution Approach 1:
The outer peripheral region is preliminarily heated before main heating to prevent thermal shock and rapid temperature rise that would cause coarse crystal particle generation. This preliminary action protects the nanosized crystal particles from coarsening during the densification process, maintaining the magnetic characteristics achieved through miniaturization.
Solution Approach 2:
The heating process applies different temperature regimes to different regions: lower temperature preliminary heating at the periphery and higher temperature main heating in the center. This local quality differentiation ensures that nanosized crystal particles throughout the powder mass are protected from coarsening while still achieving complete densification.
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 effectively prevents coarsening of crystal particles, maintaining the magnetic properties of the sintered compact and achieving a dense structure with reduced exposure to high temperatures, thereby enhancing the heat resistance and performance of the rare earth magnet.
Implementation Method 1
a heating coil is arranged around the capsule, the heating coil heats the outer peripheral region of the magnetic powder housed in the capsule
Implementation Method 2
press forming is performed while placing the preliminarily heated mass of the magnetic powder in a main heating part at second temperature T1
Implementation Method 3
press forming is performed while keeping temperature of the magnetic powder at densification temperature or higher
Data Source
AI summary
A manufacturing method for a sintered compact includes a first step in which magnetic powder is fabricated by rapid solidification, a second step in which a mass of the magnetic powder is housed in a forming mold, and preliminary heating is performed by placing the mass of the magnetic powder in a preliminary heating part of the forming mold at first temperature that is lower than coarse crystal particle generation temperature, and a third step in which main heating is performed by placing the preliminarily heated mass of the magnetic powder at second temperature that is lower than the coarse crystal particle generation temperature and higher than the first temperature, and press forming is performed while keeping temperature of the magnetic powder at densification temperature or higher.