Nd-Fe-B micro-magnet machined by diamond wire sawing: An approach on surface integrity and magnetic properties

Abstract

This study investigates the effect of diamond wire sawing on the surface integrity and magnetic properties of machined Nd-Fe-B micro-magnets. A diamond wire saw was employed to cut micro-magnets from larger sintered Nd-Fe-B magnets, varying wire cutting speed (v_c), feed rate (v_f), and micro-magnet thickness. Surface integrity and magnetic properties of micro-magnets were analyzed. The results showed that surface morphology presented microgrooving and microcutting predominance at higher v_c, while crater formation increased with higher v_f. The minimum surface roughness values achieved were S_a = 0.32 μm, S_q = 0.41 μm, and S_z = 5.93 μm. Subsurface damage included Nd₂Fe₁₄B grain pullout and intergranular microcracks, and chips exhibited a fragment-like morphology. A micro-magnet thickness of 80.4 ± 4.6 μm was successfully obtained at v_c = 5 m/s, whereas cutting micro-magnets <200 μm was challenging at 15–25 m/s. A reduction in micro-magnet thickness led to a decline in magnetic properties: for the 80.4 ± 4.6 μm micro-magnet, H_cj was 1209.5 kA/m and (BH)_max was 217.3 kJ/m³, whereas for the 495.0 ± 8.2 μm micro-magnet, H_cj reached 1403.4 kA/m and (BH)_max was 286.2 kJ/m³. The decrease in magnetic properties correlated with an increase in the machined surface-to-volume ratio. These findings indicate that diamond wire sawing is a promising micromachining process for Nd-Fe-B micro-magnets, ensuring high surface quality while maintaining excellent magnetic properties.