Wound Iron Core Bending Geometry to Prevent Cracking
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Solution Overview
Problem
The production of wound cores using grain-oriented electrical steel sheets often results in cracking, surface scratches, and insufficient shape fixability due to strict bending conditions, which can lead to reduced effective volume ratios and quality issues.
Innovation Solution
A method and device that involve bending grain-oriented electrical steel sheets with controlled plastic strain by using a one-side free bending method, where the radius of curvature of the punch and die are optimized to satisfy specific relationships, reducing plastic strain on the outer side and compression strain on the inner side, thereby minimizing cracking and improving shape fixability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If strict bending conditions are applied to form corner portions of wound core, then shape fixability is improved, but cracking occurs in bent portions and surface coating peels off
Solution Approach 1:
The patent applies parameter changes by optimizing the radius of curvature of the punch and die relative to the steel sheet thickness. Specifically, it sets the radius of curvature of the punch to 0.05 to 0.2 times the sheet thickness and the die to 0.1 to 0.4 times the sheet thickness. This parameter optimization resolves the contradiction by achieving sufficient shape fixability while minimizing cracking and coating damage through controlled strain distribution.
2Manufacturing precision
If bending radius is reduced to concentrate strain, then shape precision is improved, but processing strain becomes excessive causing cracks
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the bending radius parameters. It specifies that the punch radius should be 0.05 to 0.2 times the sheet thickness and the die radius should be 0.1 to 0.4 times the sheet thickness. This optimized parameter range achieves high shape precision for corner portions while keeping processing strain within acceptable limits to prevent cracking.
3Productivity
If repeated bending with same die is performed, then production efficiency is improved, but die scratches surface of steel sheets
Solution Approach 1:
The patent addresses this issue by optimizing the die radius parameter to be 0.1 to 0.4 times the sheet thickness. This increased radius reduces contact pressure and friction between the die and steel sheet surface during repeated bending operations, thereby preventing surface scratches while maintaining production efficiency through consistent formability.
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 minimizes cracking, prevents surface scratches and coating peeling, and enhances the effective volume ratio and shape quality of the wound core by applying appropriate plastic strain within a certain range, ensuring better productivity and shape fixability.
Implementation Method 1
controlled plastic strain by using a one-side free bending method, where the radius of curvature of the punch and die are optimized to satisfy specific relationships, reducing plastic strain on the outer side and compression strain on the inner side
Implementation Method 2
reducing plastic strain on the outer side and compression strain on the inner side, thereby minimizing cracking and improving shape fixability
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
In this method of producing a wound core, at least one bent portion (5) of one or more laminated grain oriented electrical steel sheets (1) is formed such that one side (1b) of the steel sheet (1) is placed and constrained on a die (30) and a punch (40) is press formed against a portion (1a) of the steel sheet (1) to be bent on the other free end side in the thickness (T) direction of the steel sheet. Outer surfaces of the die and the punch each have an arc portion (30a, 40a) having a predetermined curvature, and when the thickness of the steel sheet (1) is T, bent angles of the bent portions (5) are θ(°), a radius of curvature of the arc portion (30a) of the die is Rd, and a radius of curvature of the arc portion (40a) of the punch is Rp, relationships of Equations (1) to (5) below are satisfied. 0.02≤T/2Rd+T≤0.15 0.5≤Rd≤3.0 0.15≤T≤0.30 2.5≤Rp/Rd≤10 10°≤θ≤90°