A new $2.6-million project led by the University of Michigan seeks to improve electric motor efficiency, reduce costs and ultimately make the motors without heavy rare-earth elements. The 3-year project is funded by the Department of Energy Vehicle Technologies Office.
The researchers will advance an emerging technique called “laser powder bed fusion” or “selective laser melting,” which uses a laser beam to melt and fuse together material powders. With it, they will 3D-print significantly improved versions of a motor’s soft magnetic core and permanent magnets—key magnetic components that together interact with electric current in a motor to produce torque and rotation.
In today’s most efficient motors, permanent magnets attached to the spinnable rotor generate the magnetic field, and a soft magnetic core of laminated silicon steels guides the magnetic flux.
The team aims to prototype high-performance nanocrystalline soft magnetic cores and functional gradient permanent magnets. The researchers will focus on the soft magnetic core in the first phase of the project.
Conventional silicon steel cores are manufactured through a complex process that involves melting, then cold-rolling metal sheets, followed by stamping, coating and stacking the sheets to achieve the desired properties.
Since the 1960s, researchers have known that nanocrystalline soft magnetic materials such as iron silicon, or Fe-Si, and iron boron silicon doped with copper niobium, or FeBSi(CuNb), have around 10 times higher performance than silicon steel, but manufacturing approaches attempted thus far have been too expensive.
Nanocrystalline soft magnetic materials are a class of typically iron-based alloys with fine-grained, or nanoscale, crystal structure with unique magnetic properties. They have high permeability, which enables strong magnetization with relatively low magnetic fields; low coercivity, which enables rapid response to magnetic field shifts; and low eddy current losses, which translates to less energy lost in the form of heat.
By taking advantage of the rapid solidification offered by laser additive manufacturing and nanoparticle-guided nucleation, the researchers aim to 3D-print nanocrystalline soft magnetic cores layer-by-layer in the desired shapes without requiring casting, laminating, and tooling for the actual components.
In the second half of the project, the researchers will incorporate in-situ magnetization, which simply refers to magnetizing a material in place, near the melt pool to promote texturing in the printed permanent magnets, and further, fabricate gradient permanent magnets that operate without heavy rare-earth metals.
Rare-earth metals are difficult and wasteful to mine due to their low concentrations in the planet’s crust. Among them is dysprosium, a heavy silvery white metal, which is used in the permanent magnets in various types of motors. It is also among the more difficult of the rare-earths to obtain. The research team envisions manufacturing permanent magnets that don’t need dysprosium. While their approach would eliminate heavy rare-earth metals it would still require limited light rare-earth metals.
Over the course of the project, the team intends to:
- Reduce the eddy current loss by a factor of 10 for Fe-Si and FeSiB(CuNb) nanocrystalline soft magnetic materials;
- Reduce iron core loss by a factor of 5;
- Triple the permeability of the iron core;
- Decrease manufacturing costs by 40% ; and
- Eliminate dysprosium content in the permanent magnet while maintaining maximum energy product.