Abstract
Non-oriented electrical steel (NOES) laminations are commonly used to manufacture the rotor and stator core of electric machines. To achieve high machine efficiencies, it is desirable for these NOES laminations to be able to achieve a high saturation magnetisation whilst incurring minimal core losses. It is known that inappropriate machining of these laminations could cause significant deterioration in their magnetic properties. However, the mechanisms by which machining influences this deterioration are less understood. This study investigates the magnetic deterioration after four nonconventional machining methods: Abrasive Waterjet, Wire Electric Discharge Machining, Pulsed Laser, and Continuous Wave Laser.An in-depth investigation of surface integrity through a range of methods, i.e., surface topography, scanning electron microscopy (SEM), nanoindentation, electron backscatter diffraction (EBSD), and magnetic domain imaging, were conducted to study the mechanisms causing magnetic deterioration. The surface integrity after machiningusing conventional methods (e.g., microstructure and texture), was found to not be of high relevance unless this is combined with analysis on how machining affects the micro-magnetic domain structure. This paper, for the first time, highlights this aspect and attempts to make initial quantitative evaluations on how the magnetic domains are affected in the superficial layer that is the result of non-conventional machining.
Highlights
Involved in its production so that electric propulsion can be commercially competitive on a global scale [1]
Previous studies have highlighted the deterioration of the BH characteristics and specific core losses of the material observed after machining compared to the raw soft magnetic materials [7]: (i) a large increase in specific core loss, where a 23.5% increase was measured in the machined stator core compared with the supplier material data; (ii) a significant reduction in magnetic saturation, causing a 0.8% reduction in the output torque of the assembled machine
Continuous Wave Laser (CW) achieved the lowest saturation magnetisation (B = 0.5 T), and the Electric Discharge Machining (EDM) and Pulsed Laser (PL) samples exhibited similar BH behaviour to each other. This would indicate that in the Abrasive Waterjet (AWJ) sample, there is a greater proportion of magnetic domains that have the ability to become aligned with the direction of the applied field compared to the others – enabling a higher induced magnetisation
Summary
Involved in its production so that electric propulsion can be commercially competitive on a global scale [1]. Previous studies have highlighted the deterioration of the BH characteristics (where B is the measured magnetic flux density and H is the applied magnetisation) and specific core losses of the material observed after machining compared to the raw soft magnetic materials [7]: (i) a large increase in specific core loss, where a 23.5% increase was measured in the machined stator core compared with the supplier material data; (ii) a significant reduction in magnetic saturation, causing a 0.8% reduction in the output torque of the assembled machine This demonstrates the issue at hand which is, machining of a material and the corresponding surface integrity characteristics has a strong influence on the efficiency of electrical machines. It is desirable to find a process that avoids the thermal effects observed in laser and EDM, which avoids the large amount of plastic deformation that punching (mechanical cutting with a defined edge) causes For these requirements, Abrasive Waterjet (AWJ) cutting could be considered, which removes the material by directing a high velocity jet of water that is mixed with abrasive particles at the workpiece [25]. Due to these reductions in surface integrity defects after machining using AWJ cutting, it is expected that samples generated using this method will exhibit superior magnetic properties [29]
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