Wound Core Bending Hardness Control for Lower Iron Loss
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Solution Overview
Problem
The existing methods for producing wound cores, such as Unicore, introduce strain into corner portions during bending, leading to inferior iron loss performance, which can be exacerbated by incomplete strain relief during annealing, and the amount of plastic strain in bent portions is not sufficiently controlled.
Innovation Solution
A wound core is formed by stacking grain-oriented electrical steel sheets that are individually bent and connected via joining parts, with specific control of tensile stress and dynamic friction coefficient during bending to achieve an average Vickers hardness of 190 to 250 HV in the bent portions, reducing plastic strain and iron loss regardless of annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If steel sheets are bent to form corner portions of a wound core, then the conventional large-scale molding process is eliminated and processing strain is concentrated only in the bent portion, but strain is introduced into the bent portion causing core iron loss to become inferior
Solution Approach 1:
The invention changes the physical parameters of the bent portion by controlling the average Vickers hardness to be 200 HV or less through precise control of bending conditions (bending radius, bending angle, material properties). This parameter control ensures that plastic strain is minimized while still achieving the desired corner shape, thereby reducing core iron loss without requiring complete annealing
Solution Approach 2:
The invention applies local quality by concentrating the bending operation only at the corner portions rather than the entire steel sheet. The bent portions are locally formed with controlled hardness, while the rest of the steel sheet maintains its original properties. This localized approach minimizes overall strain introduction while achieving the necessary geometric transformation
2Device complexity
If the amount of plastic strain in bent portions is not sufficiently controlled, then the bending process can be simplified, but iron loss deteriorates
Solution Approach 1:
The invention implements feedback control by measuring the average Vickers hardness of the bent portion and using this information to adjust bending parameters. The hardness measurement serves as a feedback indicator of the plastic strain level, allowing the process to be tuned to achieve optimal iron loss performance while maintaining practical device complexity
Solution Approach 2:
The invention applies partial action by forming bends with specific geometric parameters (radius and angle) that are optimized to achieve adequate corner formation without excessive plastic strain. The bending is performed to the minimum extent necessary to achieve the required corner geometry, avoiding over-bending that would introduce unnecessary strain and increase iron loss
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 results in a wound core with minimized iron loss, both with and without annealing, by controlling the plastic strain within a predetermined range through precise bending parameters, ensuring low iron loss and reduced residual strain.
Implementation Method 1
any one or more of the arbitrary bent portions among the laminated grain-oriented electrical steel sheets has an average Vickers hardness of 190 to 250 HV in an L cross section
Implementation Method 2
the amount of plastic strain introduced is reduced to be within a predetermined range
Implementation Method 3
the tensile stress during steel sheet processing is in a range of 0.8 MPa or more and 6.8 MPa or less
Implementation Method 4
the dynamic friction coefficient between the steel sheet and the bending tool is in a range of 0.10 or more and 0.74 or less
Data Source
AI summary
A wound core (10) is a wound core having a wound shape (10) including a rectangular hollow portion (15) in a center and a portion in which grain-oriented electrical steel sheets (1) in which planar portions (4) and bent portions (5) are alternately continuous in a longitudinal direction are stacked in a sheet thickness direction, which is a wound core formed by stacking the grain-oriented electrical steel sheets(1) that have been individually bent in layers and assembled into a wound shape and in which the plurality of grain-oriented electrical steel sheets are connected to each other via at least one joining part (6) for each roll, wherein the bent portion (5) of the laminated grain-oriented electrical steel sheet (1) has an average Vickers hardness of 190 to 250 HV in an L cross section in the longitudinal direction which is a cross section of the grain-oriented electrical steel sheet (1) in a thickness direction.