Ring-Shaped Nd-Fe-B Magnet Moulding Die for Crack-Free Sintering
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Solution Overview
Problem
The manufacturing process of ring-shaped sintered Nd—Fe—B magnets is inefficient due to high material waste and sintering cracking issues, particularly because the inner hole processing requires separate machining, leading to low material utilization and frequent cracking.
Innovation Solution
A method involving a moulding die with a flexible cylindrical core made from alumina and zirconia powders bonded with an organic adhesive, which is embedded in the Nd—Fe—B magnetic powder, allowing for isostatic pressing and sintering without the need for separate inner hole processing, reducing cracking by ensuring even heating and shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a square green block is moulded and then machined to form a ring-shaped magnet, then the manufacturing process is simple to implement, but the material utilization rate is low (less than 60%) due to significant material waste from outer and inner diameter processing
Solution Approach 1:
The patent applies preliminary action by embedding a removable core into the green block during the moulding stage, before sintering. This core defines the inner diameter of the ring-shaped magnet in advance, eliminating the need for subsequent inner hole machining operations. The core is removed after sintering through the inner hole, leaving a clean ring-shaped magnet with high material utilization rate.
2Loss of substance
If a removable core is embedded in the green block to enable direct ring-shaped sintering, then the material utilization rate increases to 60-70%, but the inner hole is difficult to heat during sintering causing poor ring-shaped sintering shrinkage and cracking
Solution Approach 1:
The patent uses a diaphragm structure as an intermediary between the removable core and the inner hole of the green block. This diaphragm acts as a heat transfer mediator, allowing heat to reach the inner hole area more effectively during sintering. The diaphragm structure ensures uniform heating and shrinkage of the ring-shaped magnet, preventing cracking while maintaining the benefits of high material utilization.
3Ease of manufacture
If the removable core is removed from the green block before sintering, then the inner hole processing is simplified, but the process becomes time-consuming and the surface integrity of the inner hole may be damaged
Solution Approach 1:
The patent applies preliminary action by embedding the removable core during the initial moulding stage, before sintering. This allows the green block to be formed with the correct ring shape and inner diameter definition. The core is then removed after sintering through the inner hole, which is a simple and quick operation that does not damage the surface integrity, as the sintered structure provides sufficient strength.
4Ease of manufacture
If conventional machining processes are used to cut the outer circumference and inner loop, then the manufacturing process is straightforward, but the cumbersome machining process increases processing complexity and material waste
Solution Approach 1:
The patent applies preliminary action by defining both the outer shape and inner hole geometry during the moulding stage using the mould cavity and removable core. This preliminary shaping eliminates the need for complex subsequent machining operations. Only minimal finishing operations are required, significantly reducing processing complexity and material waste while maintaining ease of manufacture.
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 approach significantly improves the material utilization rate and reduces sintering cracking, achieving higher quality sintered products with enhanced material efficiency and processing ease.
Implementation Method 1
A flexible cylindrical core made from powders of alumina and/or zirconia, which are bonded with an organic adhesive
Implementation Method 2
applying an isostatic pressure to the ring-shaped green block assembly
Implementation Method 3
sintering the ring-shaped green block assembly to obtain a ring-shaped sintered blank
Implementation Method 4
thermally aging, grinding and slicing the ring-shaped sintered blank
Data Source
AI summary
The disclosure provides a preparation method, which comprises:providing a moulding die for a ring-shaped sintered Nd—Fe—B magnet;placing a Nd—Fe—B magnetic powder into the mould cavity of the moulding die in a loosely packed state, the loosely packed height of the Nd—Fe—B magnetic powder is L;placing a flexible cylindrical core into the loosely packed Nd—Fe—B magnetic powder at a L/2 position, wherein an axial direction of the flexible cylindrical core is horizontal and parallel to the direction of a magnetic field in the mould cavity;applying a vertical pressure to the Nd—Fe—B magnetic powder to obtain a ring-shaped green block assembly with the flexible cylindrical core embedded;after encapsulating and isolating the ring-shaped green block assembly, applying an isostatic pressure to the ring-shaped green block assembly;sintering the ring-shaped green block assembly to obtain a ring-shaped sintered blank;thermally aging, grinding and slicing the ring-shaped sintered blank.