Localized Induction Heat Treatment of Electric Motor Stator Laminations
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Solution Overview
Problem
Residual stress in electrical steel, induced by stamping processes, leads to increased core loss and reduced energy efficiency in electric machines due to the magnetic permeability variations and torque ripple phenomena.
Innovation Solution
A localized induction heat treatment method is applied to electrical steel laminations, focusing on edge areas to reduce residual stress and core loss by generating eddy currents with a changing magnetic field, thereby increasing magnetic permeability and reducing parasitic magnetic flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If stamping steel into laminations is performed to form stator and rotor components, then the desired shape and structure are achieved, but residual stress is induced which increases core loss and reduces magnetic permeability
Solution Approach 1:
The patent applies localized induction heating specifically to the edge areas of laminations where residual stress is most concentrated, rather than heating the entire lamination uniformly. This localized approach reduces core loss in the critical stress regions while maintaining the overall structural integrity and magnetic properties of the lamination body.
Solution Approach 2:
The patent changes the physical state of the steel by applying controlled thermal energy through induction heating, transforming the residual stress state from a high-stress condition to a relaxed condition. This parameter change (thermal treatment) restores magnetic permeability and reduces core loss without altering the lamination shape.
2Loss of energy
If traditional annealing is applied to reduce residual stress, then core loss decreases, but the process requires significant time and energy consumption
Solution Approach 1:
Instead of applying uniform annealing across the entire lamination, the patent uses localized induction heating targeted at edge areas where residual stress is most problematic. This localised approach dramatically reduces the total energy required for heat treatment while achieving the same core loss reduction effect.
Solution Approach 2:
The patent replaces traditional furnace-based thermal annealing with induction heating technology. This substitution uses electromagnetic fields to generate heat directly within the steel material, eliminating the need for external heat transfer through air or contact, thereby reducing energy consumption and processing time.
3Stability of the object's composition
If uniform heat treatment is applied across the entire lamination, then residual stress is reduced, but the time and power required for heat treatment increases significantly
Solution Approach 1:
The patent identifies that residual stress is not uniformly distributed across the lamination but is concentrated at the edges where stamping operations create the most deformation. By targeting only these edge regions with induction heating, the patent achieves stress relief in the critical areas without the time penalty of treating the entire lamination.
Solution Approach 2:
The patent applies heat treatment to only the necessary portions of the lamination (the edge areas with highest residual stress) rather than the entire component. This partial action approach achieves sufficient stress relief to reduce core loss while minimizing the time and energy investment required.
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 method decreases core loss by 2-10% and reduces energy consumption, while also minimizing the time and power required for heat treatment, thereby enhancing the efficiency and performance of electric machines.
Implementation Method 1
exposing the laminations to a changing magnetic field such that, for each of the laminations, a density of resulting eddy currents is greatest near the inner edge area to heat the same relative to central areas of the lamination
Implementation Method 2
exposing the laminations to a changing magnetic field such that, for each of the laminations, a density of resulting eddy currents is greatest near the inner edge area
Implementation Method 3
The residual stress, and in turn, core loss may be reduced by a metal working process called annealing. Annealing is a heat treatment process that alters the physical and sometimes chemical properties of the material being treated.
Data Source
AI summary
A method of manufacturing a stator is provided. The method may include stamping steel into laminations each having an inner edge area defining a residual stress associated with a magnetic permeability. The method may also include exposing the laminations to a changing magnetic field such that, for each of the laminations, a density of resulting eddy currents is greatest near the inner edge area to heat the same relative to central areas of the lamination to decrease the residual stress and core loss.