Carbon Mold for NdFeB Magnet Sintering
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Solution Overview
Problem
Conventional press-less processes for producing NdFeB sintered magnets using expensive, difficult-to-machine, and embrittling metals like Mo, W, Ta, and Pt result in deformation and low product yield due to reactivity with Fe—Ni alloy molds, and the use of coated Fe—Ni alloy molds still leads to curvature issues.
Innovation Solution
Employing a mold with at least a carbon material part to reduce friction and prevent deformation, combined with ferromagnetic materials for improved magnetic field orientation, and using a carbon material for the mold's bottom to manage sintering shrinkage and prevent impurity contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a mold made of Fe—Ni alloy is used, then the mold is inexpensive and easy to machine, but the alloy powder reacts with or strongly adheres to the mold causing deformation
Solution Approach 1:
A coating layer is applied to the inner surface of the Fe—Ni alloy mold to act as an intermediary between the mold and the alloy powder. This coating prevents direct contact and chemical reaction between the Fe—Ni alloy mold material and the alloy powder, eliminating adhesion and deformation issues while retaining the advantages of Fe—Ni alloy mold material.
2Reliability
If a mold made of Mo, W, Ta, or Pt is used, then the mold does not react with alloy powder, but the mold is expensive, difficult to machine, and embrittles when heated
Solution Approach 1:
The patent replaces expensive, difficult-to-machine noble metals (Mo, W, Ta, Pt) with a more economical Fe—Ni alloy mold that is coated with a protective layer. This substitution significantly reduces material cost and machining difficulty while the coating maintains the chemical stability needed to prevent reaction with alloy powder.
3Reliability
If a coated Fe—Ni alloy mold is used, then the reaction with alloy powder is prevented, but the sintered compact becomes curved or deformed
Solution Approach 1:
The patent optimizes the coating thickness and material properties to control friction characteristics. By adjusting the coating parameters, the friction between the sintered compact and mold is reduced to an appropriate level that allows uniform shrinkage during sintering, preventing curvature and deformation while maintaining chemical stability.
4Strength
If the friction between mold and sintered compact is high, then the mold provides structural support, but the shrinkage of sintered compact is impeded causing curvature
Solution Approach 1:
The patent applies a coating with specific friction characteristics to the inner surface of the mold, creating a localized interface property that differs from the bulk mold material. This coating provides appropriate low friction to reduce restraint on sintered compact shrinkage, while the overall mold structure maintains sufficient structural support.
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
The method enables the production of NdFeB sintered magnets without curvature or deformation, utilizing inexpensive and easily machined carbon materials that maintain structural integrity, while ensuring high magnetic properties and increased product yield.
Implementation Method 1
applying a magnetic field to the alloy powder to align the crystal orientation of the powder
Implementation Method 2
the friction between a carbon material and the sintered compact is lower than that between the material of a conventional mold and the sintered compact
Implementation Method 3
heating the whole container with the alloy powder filled therein to be sintered
Data Source
AI summary
A mold which is inexpensive and easy to process and does not embrittle. Also provided is a process by which a sintered NdFeB magnet can be produced using the mold without suffering bending or deformation. At least part (e.g., a bottom plate) of the mold is made of a carbon material. Carbon materials have lower friction with a sinter during sintering than metals. The mold hence enables a sintered NdFeB magnet to be produced without suffering the bending or deformation caused by friction due to sintering shrinkage. Carbon materials are inexpensive and easy to process. The mold does not embrittle even when repeatedly used. Such effects can be significantly produced when a carbon material is used as the bottom plate, on which the load of the sinter is imposed during sintering.