Comparative effect of tolerance-controlled multi-wire sawing versus grinding on surface damage and mechano-magnetic properties of sintered Nd-Fe-B thin magnets

Sintered Nd-Fe-B thin magnets are highly sensitive to surface defects, which critically affect their performance. This study systematically compares the effects of tolerance-controlled multi-wire sawing (using a Ø120 μm diamond wire) and conventional grinding on surface integrity and mechano-magnetic properties. Both processes met the required assembly tolerances; however, while grinding provided slightly better flatness and dimensional consistency, it introduced severe subsurface damage and grain pull-out. In contrast, the multi-wire-sawn samples retained superior surface integrity with a dense and intact surface layer. This resulted in a microhardness of 675.2 HV, approximately 4.5% higher than that of ground samples and a 9.8% increase in the mean three-point bending force (54.8 N), with no low-strength outliers observed. Moreover, the multi-wire-sawn magnets exhibited an approximately 1.78% higher magnetic moment per unit mass and an approximately 0.54% lower irreversible flux loss after exposure at 100 °C for 2 h. Microstructural analysis revealed that the tolerance-controlled sawing process effectively preserved the surface layer, which suppressed reversed magnetization nucleation. These findings demonstrate that this process can synergistically enhance mechanical and magnetic properties while maintaining dimensional accuracy, offering a theoretical foundation for low-damage and high-efficiency manufacturing of sintered Nd-Fe-B thin magnets.