Sintered NdFeB Magnet Green Compact Machining
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Solution Overview
Problem
Large size NdFeB magnets experience component segregation and magnetic property attenuation due to rare earth volatilization and machining-induced surface stress during sintering and annealing, while traditional machining methods are inefficient and damage-prone, especially for products with complex shapes.
Innovation Solution
A method involving pressing magnetic powders into green compacts under a magnetic field, followed by isostatic pressing, precise machining of the green compact into a finished shape, and subsequent sintering and annealing, using a special device with a reciprocating cutting mechanism and cutting tooling to minimize damage and enhance precision, and finally conventional machining of the sintered blank.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional machining methods are used on annealed blanks, then machining efficiency and precision are high, but surface stress damages the crystal structure causing magnetic property attenuation
Solution Approach 1:
The patent applies preliminary machining to the green compact before sintering to create the finished product shape. By performing machining operations on the green compact rather than the sintered blank, the method avoids generating surface stress that would damage the crystal structure and attenuate magnetic properties, while still achieving the required dimensional precision through subsequent minimal finishing operations
2Reliability
If green compact is machined into finished product before sintering, then magnetic property damage is avoided, but machining precision is poor and pass rate is reduced
Solution Approach 1:
The patent applies partial machining to the green compact, processing only the surfaces that will be exposed in the final product while leaving the interior structure intact. This partial machining approach achieves the necessary surface precision and shape accuracy without requiring complete machining of the green compact, thereby maintaining higher pass rates while still avoiding the magnetic property damage associated with traditional post-sintering machining
3Reliability
If green compact is machined directly into product size, then machining-induced damage is reduced, but surface area increases causing easier nitride forming or oxidation
Solution Approach 1:
The patent performs preliminary machining on the green compact to establish the finished product shape before sintering. By creating the final geometry in the green state and then performing only minimal finishing operations after sintering, the method minimizes the total surface area exposed to oxidation and nitride formation during machining operations, while still achieving the required dimensional accuracy and avoiding the magnetic property damage of traditional methods
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 improves the uniformity and magnetic properties of sintered NdFeB magnets, reduces waste, and increases the comprehensive utilization rate of magnetic powder by minimizing machining-induced losses and oxidation, resulting in enhanced product uniformity and magnetic performance.
Implementation Method 1
pressing magnetic powders into a green compact under a magnetic field
Implementation Method 2
isostatic pressing the green compact
Implementation Method 3
sintering and annealing the machined green compact
Implementation Method 4
sintering and annealing the machined green compact
Data Source
Figure 1
Figure 2~3
AI summary
There is provided a method of preparing a sintered NdFeB magnet comprising the steps of: a) pressing magnetic powders into a green compacts under a magnetic field and then demagnetization; b) isostatic pressing the green compact; c) fixing the green compact on the special device as defined in claim 8, and then machining the green compact into a finished shape and corresponding size on one or two surfaces among an orientation surface, non-orientation surface and pressing surface; d) sintering and annealing the machined green compact; and e) machining the obtained blank into a finished product. Further, a corresponding special device is disclosed.