Carbide twist drill surface polishing and cutting edge passivating based on magnetic field-assisted shear thickening

The multi-field compound polishing method based on the shear thickening has been applied to the processing of various hard materials due to its characteristics of low damage and adaptability to complex surface shapes. The surface/subsurface defects on the carbide twist drill are caused during the grinding. This paper proposes a magnetic field-assisted shear thickening polishing (MASTP) method based on shear thickening and pumping effect, aiming to remove microscopic defects of twist drill cutting edge and passivate cutting edges to improve its cutting performance. The microscopic materials removal mechanism of cemented carbide and the rheological properties of magnetic shear thickening fluid (MSTF) were analyzed. The magnetic field intensity distribution in the polishing area for two types of magnetic pole arrangements (uniform and spiral arrangement) is simulated. A numerical model was used to investigate the effect regularity of the polishing gap and spindle speed on the flow field shear stress. Experimental validation was carried out based on the processing platform. The results show that the effects of processing parameters on twist drill surface roughness improvement rate and edge radius correspond to the simulated shear stress. After 60 min of polishing, the surface roughness improvement rate reached 94.7% and 80.4% at the body clearance and margin, respectively. The passivating radius of the major cutting edge can reach 12.92 µm, while the passivating radius of the minor cutting edge can reach 15.73 µm. At the same time the edge defects caused by the grinding are also removed.