Grinding damage in the fabrication of polycrystalline cubic boron nitride micro-drill

Micro superhard cutting tool such as polycrystalline cubic boron nitride (PCBN) tool are increasingly demanded in high-end manufacturing field. The grinding is a widely used technology in the manufacture of superhard micro-tools, but its grinding damage is often difficult to control. In order to improve the grinding quality of superhard micro-tools, it is necessary to further understand the damage behavior during tool grinding process. This study aims to reveal the damage form and damage formation mechanism in the grinding process of PCBN micro-drills. The PCBN micro-drill grinding experiment is conducted under different process parameters, and the morphology characteristics of the micro-drill surface and cutting edge are observed and analyzed. The influence of grinding process parameters on the grinding quality of PCBN micro-drill is quantitatively investigated. The results indicate that, the grinding damage of PCBN micro-drill is mainly manifested as micro chipping and micro fracture of the cutting edge, material adhesion on the chisel edge, and micro cracks, micro pits and micro scratches on the grinding surface. For the ground surface of flank and helical flute of PCBN micro-drill, the material removal mechanisms of plastic removal and brittle removal work together. The material in the area with more binder inclusions is removed by plastic removal mode, and the material brittleness removal mode mainly includes cleavage brittleness removal and intergranular brittleness removal. The edge impact fracture brings grinding damage to the main cutting edge of PCBN micro-drill. The CBN grains at the fracture surface mainly undergo cleavage fracture, while the fracture of the binder occurs in the form of micro pit aggregation. The reduction of grinding depth and feed rate will lead to the decrease in the surface roughness of flank and helical flute, the cutting edge radius, and the edge chipping width, thus improve the grinding quality of PCBN microdrill. These findings contribute to expand the understanding of process characteristics for grinding PCBN micro-tools, and thus to restrain the grinding damage and improve the grinding quality of micro-tools.