Interior Permanent Magnet Rotor Shrink Fitting and Bond Magnet Injection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional interior permanent magnet-type inner rotors experience thermal demagnetization during shrink fitting, leading to increased size and rare-earth element usage, and manufacturing challenges such as deformation and magnetization issues.
Innovation Solution
The method involves shrink-fitting the rotor core to the rotating shaft and then filling slots with a flowable mixture of anisotropic magnet particles and binder resin in oriented magnetic fields, avoiding high temperatures that cause demagnetization, and using a three-layer mold structure for precise molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the inner rotor is heated to high temperature for shrink fitting, then the rotor core can be fixed to the rotating shaft, but thermal demagnetization occurs and permanent magnet strength decreases
Solution Approach 1:
The patent applies preliminary action by pre-heating the rotor core to a temperature below the Curie point of the permanent magnets (e.g., 150-200°C) before shrink fitting, and then completing the heating to the required shrink fitting temperature (e.g., 300-500°C) after the magnets are installed. This sequence prevents thermal demagnetization while achieving the necessary interference fit between the rotor core and rotating shaft.
2Reliability
If sintered rare-earth magnets are used, then magnetic poles can be formed, but the cross-sectional shape is limited and processing is difficult leading to high cost
Solution Approach 1:
The patent changes the manufacturing parameters by transitioning from sintered magnets to injection-molded bond magnets. This allows the magnetic poles to be formed directly in complex cross-sectional shapes (such as circular arc or elliptical shapes) during injection molding, eliminating the need for difficult cutting and polishing processes while maintaining magnetic performance through proper formulation of the magnet powder and binder resin mixture.
3Manufacturing precision
If sintered magnets are cut and polished into predetermined dimensions, then precise dimensions can be achieved, but the process is difficult and costly
Solution Approach 1:
The patent replaces the mechanical cutting and polishing system with an injection molding system. The magnetic poles are formed by injecting a flowable mixture of magnet powder and binder resin into molds with the desired cross-sectional shape, allowing precise dimensional control through mold design rather than mechanical machining, thereby simplifying the manufacturing process.
4Ease of manufacture
If simple plate-like shaped sintered magnets are used, then manufacturing is easier, but defects occur during insertion into slots
Solution Approach 1:
The patent changes the physical state parameter of the magnet material from solid sintered blocks to a flowable mixture of magnet powder and binder resin. This flowable state allows the magnetic material to be easily injected into slots and conform to complex slot geometries without causing defects, while the binder resin ensures proper bonding and structural integrity after solidification.
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 prevents thermal demagnetization, allows for reduced motor size and cost, and simplifies the manufacturing process by eliminating the need for separate magnetization steps, while enabling the use of existing facilities with minimal additional investment.
Implementation Method 1
filling the slots of the rotor core in a residual heat state after the shrink fitting step with a flowable mixture in oriented magnetic fields, the flowable mixture being a mixture of a binder resin heated to a flowable state and anisotropic magnet particles, forming anisotropic bond magnets as magnetic poles in a solidified state of the flowable mixture
Implementation Method 2
An inner rotor may often be fixed to a rotating shaft as that of a motor or as the driving shaft of a device by shrink fitting. This shrink fitting is performed by heating the inner rotor to a high temperature (ordinarily 300 to 500 degrees C).
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
An object is to provide a manufacturing method that allows an interior permanent magnet-type inner rotor to be obtained without occurrence of thermal demagnetization due to shrink fitting to a rotating shaft. The manufacturing method of the present invention is characterized by comprising: a shrink fitting step of heating a rotor core (1) having slots and inserting a rotating shaft (20) into a shaft hole to shrink-fit the rotor core ; and a filling step of filling the slots of the rotor core in a residual heat state after the shrink fitting step with a flowable mixture in oriented magnetic fields, the flowable mixture being a mixture of a binder resin heated to a flowable state and anisotropic magnet particles. This makes it possible to obtain, in similar manufacturing steps, an inner rotor (10) of which the magnetic poles are anisotropic bond magnets formed by solidifying the flowable mixture in the slots and a conventional inner rotor of which the magnetic poles are sintered magnets. As a result, it is also facilitated to produce both the inner rotors concurrently and in parallel (mixed flow production) in an already existing IPM motor manufacturing line.