Fabrication and performance of CVD diamond cutting tool in micro milling of oxygen-free copper

Abstract

Chemical vapor deposited (CVD) diamond is a promising material to fabricate micro-cutting tools owing to its ultra-high hardness, Young's modulus, and isotropic characteristics. In this research work, a novel compound process of laser-induced graphitization coupled with precision grinding, was proposed to fabricate CVD diamond micro-milling tool. The diamond-graphite transition behavior and mechanisms were specifically investigated. The microstructure of the graphite layer and the graphite-diamond boundary layer were observed with a scanning electron microscope (SEM) and three-dimensional confocal microscopy. Under laser irradiation, a loose graphite layer and heat-affected layer (defined as boundary layer) were formed on the CVD diamond matrix. Findings have depicted that a thermal conduction process dominated diamond-graphite transition. With decreasing the laser fluence, the thicknesses of both graphite layer and boundary layer were also reduced. The diameter, cutting edge radius, and nose radius of the fabricated CVD diamond micro-milling tool were 0.4 mm, 2.3 μm and 2.5 μm, respectively. The performance of the cutting tool was studied with regard to micro-milling of oxygen-free copper. The performance of the CVD diamond tool was ensured by comparing it with commercially purchased coated cemented carbide tools under identical machining conditions. The resultant forces, machined surface quality, burr formation, and tool failures were investigated. The results have indicated that lower resultant forces, less burr formation, and minimum surface roughness (arithmetic average surface roughness Ra of 53 nm) were obtained with the CVD diamond tool. The failure of the CVD diamond tool was characterized by flaking and flank/rake face wear, while the cemented carbide tool failure was associated with extensive flaking, coating spalling and flank face wear. The experimental study has shown superior performance of the fabricated CVD diamond tool as compared to commercially purchased coated cemented carbide tool. This work validates a feasible fabrication process of CVD diamond micro-milling tool, and a practical micro-machining data using CVD diamond tool.