Non-Oriented Electrical Steel Grain Control for Core Roundness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Non-oriented electrical steel sheets used in motor cores often experience a decrease in dimensional accuracy due to non-uniform residual stress distribution after punching, leading to reduced roundness and increased cogging torque during core annealing.
Innovation Solution
A non-oriented electrical steel sheet with a controlled crystal grain structure, where the area proportion of crystal grains with a crystal grain size less than 200 μm and a crystal orientation difference of 2° to 15° is limited to 10% or less, and the ratio of maximum to average crystal grain size is constrained to 5.0 or less, along with specific chemical composition and manufacturing conditions to ensure uniform stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If core annealing is performed to reduce iron loss, then magnetic properties are improved, but dimensional accuracy and roundness decrease due to non-uniform residual stress release
Solution Approach 1:
The patent applies preliminary action by controlling the crystal grain structure before core annealing to prevent non-uniform stress distribution. Specifically, the steel sheet is designed with restricted crystal grain size (maximum 200 μm) and controlled grain boundary characteristics (area proportion of grains with 2-15° orientation difference ≤10%) prior to punching and annealing processes. This pre-established uniform microstructure ensures uniform residual stress distribution during subsequent punching, which then releases uniformly during core annealing, maintaining dimensional accuracy while achieving the desired magnetic properties through iron loss reduction.
2Ease of manufacture
If punching is performed to shape the stator core, then the core geometry is formed, but non-uniform residual stress distribution occurs leading to shape distortion
Solution Approach 1:
The patent applies parameter changes by modifying the microstructural parameters of the steel sheet before punching. The crystal grain size is controlled to be 200 μm or less, and the area proportion of crystal grains with orientation differences of 2° to 15° is limited to 10% or less. These parameter changes in the material's microstructure create more uniform mechanical properties throughout the steel sheet, which in turn produces more uniform residual stress distribution during the punching process. This uniform stress distribution minimizes shape distortion and maintains roundness after punching operations.
3Stability of the object's composition
If crystal grain size is reduced to improve uniformity, then residual stress distribution becomes more uniform, but manufacturing complexity increases
Solution Approach 1:
The patent establishes specific parameter ranges for crystal grain size (maximum 200 μm) and grain boundary characteristics (area proportion of grains with 2-15° orientation difference ≤10%) that achieve uniform stress distribution. These quantified parameters provide clear manufacturing targets that balance uniformity achievement with process feasibility.
Solution Approach 2:
The patent applies local quality by focusing control efforts on specific critical microstructural features rather than attempting to control all aspects of the material. Specifically, it targets crystal grain size and grain boundary orientation characteristics as the key local features that influence residual stress distribution. By concentrating control on these specific local properties, the patent achieves uniform stress distribution without requiring complex manufacturing processes.
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 suppresses the decrease in dimensional accuracy after processing and core annealing, maintaining high roundness and reducing cogging torque, thereby improving motor performance by ensuring uniform stress release and maintaining magnetic properties.
Implementation Method 1
an area proportion of crystal grains having a crystal grain size of less than 200 μm is 10% or lower when a boundary with a crystal orientation difference of 2° or more and less than 15° is regarded as a crystal grain boundary
Implementation Method 2
it is subjected to core annealing to reduce iron loss. Specifically, a rotor core is first punched out of a non-oriented electrical steel sheet, then the inner diameter of a stator core is punched out, and then the outer diameter of the stator core is punched out. By applying heat to the stator core through core annealing, residual stress and strain are released, and iron loss is reduced.
Data Source
AI summary
In this non-oriented electrical steel sheet, an area proportion of crystal grains having a crystal grain size of less than 200 μm is 10% or lower when a boundary with a crystal orientation difference of 2° or more and less than 15° is regarded as a crystal grain boundary in a cross section parallel to a steel sheet surface.