An inclined-tip burnishing method with active rotary tool was applied to control the surface microstructure of non-oriented electrical steel sheets in order to improve their magnetic properties. The burnishing tools used were made of zirconia and DLC-coated cemented tungsten carbide, which have significantly different thermal conductivities, and the effect of differences in the temperature of the burnished area due to frictional heat on the controllability of the surface microstructure was examined. The tool path of the burnishing process clearly influenced the flow behavior of the surface material. For zirconia tool, the temperature rise at the burnishing point was higher than for DLC-coated tool. Additionally, the width and depth of the burnishing scar were larger, and the burnishing-affected zone was deeper. When zirconia tool was applied at high sliding speed and low thrust force, crystalline grains were clearly observed extending to the outermost surface layer compared to before burnishing. Analysis of the crystalline structure of the outermost layer using X-ray diffraction revealed that applying a burnishing process reduced the intensity of diffraction peaks and increased the full width at half maximum compared to the untreated state. The crystal orientation control was also possible through the burnishing conditions. Evaluation tests of motor cores revealed that magnetic properties varied with burnishing conditions. Analysis of the electromotive force waveform when varying the input rotational speed suggested that burnishing process could potentially reduce eddy current losses in the non-oriented electrical steel.
Okada et al. (Thu,) studied this question.