Heat Where It Matters: Spatially Tuned Soft Magnetic Alloys for Higher-Efficiency Electric Motors

This invention is a thermal processing method that uses electromagnetic fields to heat a soft magnetic alloy component from the inside, so that different regions of the same part receive different thermal treatments. This lets a single component combine low magnetic loss where efficiency matters with high mechanical strength where durability matters.

Description

Unmet Need - Conventional uniform annealing forces a trade-off between magnetic efficiency and mechanical strength in motor laminations, and this method tailors that balance within a single component.

Soft magnetic alloys, such as iron-cobalt alloys and electrical steels, are used in the rotors and stators of electric motors. Traditionally, the whole part is heated in a furnace, so strength and magnetic performance are set together. Improving one usually costs the other.

In this method, an electromagnetic field (RF, microwave, or optical) is applied to the component. The field generates heat internally within the material, so the temperature can differ from one region to another. Because magnetic and mechanical properties such as core loss, permeability, yield strength, and hardness depend on the thermal treatment, they vary across the component in a controlled way. The field can be delivered through a coil, such as a helical, split helical, or pancake coil. Coil current can be concentrated above the regions meant to run hottest, for example the outer or inner diameter of a rotor or stator, or the stator teeth. The method can be applied to laminations before stamping, preserving a radial temperature dependence for complex geometries.

Applications

- Surface-mounted and interior permanent magnet motors, induction machines, and switched reluctance machines
- Electric vehicle traction motors (rotor and stator laminations)
- Hybrid-electric and electric aircraft propulsion motors
- Axial flux motors
- Surface-mounted and interior permanent magnet motors, and induction machines
- Advanced soft magnetic alloy laminations for other electromagnetic components

Advantages

- Spatially varying magnetic properties and mechanical properties within a single component
- Heat generated internally by the electromagnetic field, giving localized, well-controlled thermal profiles
- Can reduce core loss in high-flux regions while keeping strength in the regions that bear mechanical load
- Compatible with bulk crystalline alloys, including iron-cobalt alloys and electrical steels
- Flexible implementation: several field types and coil geometries, and heating and cooling rates as high as 10²–10⁴ K/s

Invention Readiness

The concept has been demonstrated at laboratory scale. Simulations predict the steady-state temperature distribution in an iron-cobalt laminate heated with an RF induction coil. They also show how loss and yield strength would vary across the part. Experimental measurements of yield strength versus annealing temperature and of core loss versus yield strength were used to inform these simulations.

IP Status

https://patents.google.com/patent/US12709780B2

Related Publication(s)

Talaat, A., Greve, D. W., Suraj, M. V., & Ohodnicki, P. R. (2021). Electromagnetic assisted thermal processing of amorphous and nanocrystalline soft magnetic alloys: Fundamentals and advances. Journal of Alloys and Compounds, 854, 156480. https://doi.org/10.1016/j.jallcom.2020.156480

Byerly, K., Ohodnicki, P. R., Moon, S.-R., Leary, A. M., Keylin, V., McHenry, M. E., Simizu, S., Beddingfield, R., Yu, Y., Feichter, G., Noebe, R. D., Bowman, R., & Bhattacharya, S. (2018). Metal amorphous nanocomposite (MANC) alloy cores with spatially tuned permeability for advanced power magnetics applications. JOM, 70(6), 879–891. https://doi.org/10.1007/s11837-018-2857-5