Sharpening mechanism of extremely sharp edges for diamond micro mills

Abstract

• This study explores the sharpening mechanism of extremely sharp edges for PCD micro mills. • The transient temperature model of laser cutting PCD is constructed for studying the material removal mechanism . • The uniform graphitisation , micro abrasion , and smaller material stress near edge contribute to the extremely sharp edges. • The PCD micro mills with cutting edge radius of r β = 0.21 μm are fabricated indicating better sharpness compared with r β = 1–5 μm reported hitherto. The fabrication of extremely sharp cutting edges for ultra-hard micro mills is crucial for suppressing the severe size effect, restraining burr formation, and improving the surface quality of widely used micro components in micro milling. In this study, a hybrid machining technique, laser-assisted precision grinding, is proposed to improve the grinding efficiency and increase the sharpness of the cutting edges of polycrystalline diamond (PCD) micro end mills. A transient heat model of laser ablation was constructed to investigate the laser-cutting mechanism of PCD with a cobalt binder. Facilitated by suitable heat conduction, cobalt absorbs photon energy to heat itself and transmits thermal energy to the surrounding diamond, resulting in uniform graphitisation and cobalt oxidation on the cut section. Hence, the affected layer on the cut section can be easily ground using a low grinding load. Moreover, the subsequent grinding mechanism of the laser-cut section was demonstrated. The diamond was removed via micro-abrasion without any intercrystalline cracks or grain dislodgement, and the abrasive grain size was optimised to achieve superior ground surface quality. Thus, the uniform graphitization, micro abrasion, and smaller material stress near edge contributed to the extremely sharp edges. Furthermore, PCD micro end mills with a diameter of 400 μm, aspect ratio of 2, and cutting-edge radius of approximately 0.2 μm were fabricated, showing a superior sharpness compared with that of the end mills with an edge radius of 1–5 μm reported hitherto. Subsequently, micro-milling experiments were conducted on oxygen-free high-conductivity copper (OFHC) using the self-fabricated PCD micro end mills. Almost no burrs were observed, and the surface roughness of the machined groove was 19.8 nm, indicating the superior cutting performance of the fabricated PCD micro end mills.