Rotor Core Bridge Strengthening via Local Grain Refinement
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Solution Overview
Problem
Existing methods for manufacturing rotary electric machine rotors struggle to achieve both finer grains in steel sheets for increased strength and prevent the resulting hardness from increasing pressing equipment size and reducing die life.
Innovation Solution
A method involving punching steel sheets, applying mechanical or high-density energy to specific parts to induce plastic strain, and subsequent heat treatment to achieve finer grains and enhance strength, particularly at bridge portions, while maintaining manageable equipment size and die longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If grains in steel sheets are made finer to increase strength, then rotor strength increases, but the sheet before punching becomes harder leading to increased pressing equipment size and decreased die life
Solution Approach 1:
The steel sheet processing is divided into two distinct stages: first punching with coarser grains for ease of manufacturing, then applying plastic strain and heat treatment to specific local regions (bridge portions) to achieve fine grains and increased strength only where needed. This segmentation allows each stage to optimize for its specific goal without compromising the other.
Solution Approach 2:
Instead of making the entire steel sheet with fine grains, the invention applies plastic strain and heat treatment only to specific local regions (bridge portions) where strength is critical. This creates local fine-grain structures with high strength while maintaining coarser grains in other areas, thus avoiding the need for oversized pressing equipment and extending die life.
2Strength
If local strength at bridge portion is increased by heat treatment after rotor core assembly, then some strength improvement is achieved, but finer grains of steel sheets cannot be achieved leading to insufficient strength
Solution Approach 1:
The invention applies plastic strain to the steel sheet before stacking to form the rotor core. This preliminary action creates a deformed structure that, when subsequently heat-treated, produces fine grains more effectively. The plastic strain prepares the material structure in advance, enabling the heat treatment to achieve finer grains and greater strength improvement than post-assembly heat treatment alone.
Solution Approach 2:
The invention replaces conventional post-assembly heat treatment with a combined approach: mechanical plastic strain followed by heat treatment. The mechanical energy input through plastic strain modifies the material structure, enabling the subsequent thermal energy to produce finer grains and superior strength characteristics compared to thermal treatment alone.
3Productivity
If electromagnetic steel sheets with higher strength are used for downsizing and higher-speed rotation, then motor performance improves, but manufacturing difficulty increases due to sheet hardness
Solution Approach 1:
The manufacturing process is segmented into stages with different material properties: initial punching uses standard coarser-grain sheets for ease of manufacture, while subsequent localized heat treatment creates fine-grain high-strength regions. This allows the rotor to achieve high-performance characteristics without requiring the entire steel sheet to be difficult-to-manufacture high-strength material.
Solution Approach 2:
The invention changes the grain size parameter locally through plastic strain and heat treatment. By transforming the microstructure from coarse to fine grains in specific regions, the material properties are altered to achieve higher strength and performance characteristics without changing the overall material composition or requiring difficult-to-manufacture high-strength steel sheets throughout.
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 effectively increases rotor strength, downsizes pressing equipment, and extends die life without compromising iron loss characteristics in the stator core.
Implementation Method 1
a step of causing plastic strain before or after the stacking step by applying mechanical energy or high-density energy to at least one steel sheet out of the plurality of steel sheets
Implementation Method 2
a step of applying heat to the steel sheet in which the plastic strain has been caused
Data Source
AI summary
A method for manufacturing a rotor or a rotary electric machine having magnet holes. The method includes a step of preparing a plurality of steel sheets punched out of a material by pressing, a step of stacking the plurality of steel sheets to form a rotor core, a step of causing plastic strain by applying mechanical energy or high-density energy to at least one steel sheet out of the plurality of steel sheets, and a step of applying heat to the steel sheet in which the plastic strain has been caused.