Mechanism and characterization of laser-assisted hybrid processing for chemical vapor deposited diamond micro milling cutters

Abstract

The fabrication of superhard micro milling cutters with extreme sharpness is highly demanded to meet the strict requirements of micro structures in terms of machining accuracy, surface roughness and burr height. In this study, nanosecond laser induced graphitization assisted grinding was proposed by considering machining efficiency and machining quality simultaneously for chemical vapor deposited (CVD) diamond micro flat-end milling cutters. An optimal cut-section was obtained by adopting moderate laser cutting energy and avoiding unstable thermodynamic coupling effect. The following laser induced graphitization mechanism on the cut-section was studied by analysing the different graphitization behaviours. The extensive graphitization caused sintered and banded graphite while the weak graphitization could not eliminate the defects caused by laser cutting. The uniform and dense graphitization resulted from appropriate energy distribution contributed to the smooth transition layer which was the significant factor in subsequent grinding. Moreover, the subsequent grinding behaviours of different transition layers were investigated, the grooved defects on transition layer caused the unstable grinding and fracture removal model, leading to the cracked ground surface and blunt cutting edge. Nevertheless, the grinding model of smooth transition layer was scratching without transcrystalline cracks, resulting in the smooth ground surface and sharp cutting edge. Thus, the laser parameters were finally optimized based on the feedback. Furthermore, the even graphitization, undamaged transition layer, scratching, as well as less material stress resulted in the extreme sharpness. In this way, the CVD diamond micro flat-end milling cutter (CVDM) with a diameter of 200 μm, surface roughness Sa of 30 nm, aspect ratio of 3, and edge radius of around 0.12 μm was prepared, the extreme sharpness was indicated by comparing with the edge radius of 1–5 μm reported heretofore. Finally, the micro grooves with surface roughness Sa of 17.8 nm and tiny burrs were machined on Ti-6Al-4 V by the homemade CVDM, which thereby indicated the outstanding cutting performance of the CVDM in micro-milling.