Milling performance of diamond-coated tools with varying flute numbers and diamond grain sizes in graphite machining

The rising demand for 3D curved glass in electronics has rendered the efficient and precise machining of graphite molds a critical challenge. This study develops diamond-coated ball-end mills with varying diamond grain sizes and flute numbers to mitigate the severe tool wear and inconsistent surface quality observed in high-speed graphite milling. Diamond coatings with three distinct grain sizes were synthesized via hot filament chemical vapor deposition (HFCVD), and their mechanical properties, wear mechanisms, and the resulting machined surface quality were evaluated through microscopic characterization and milling experiments. Results indicate that four-flute tools initially yield lower surface roughness; however, this roughness increases markedly over time, compromising machining stability compared to two-flute tools. Coarse-grained coatings, owing to their superior resistance to abrasive wear, extended tool life to 300 min without delamination, whereas fine-grained coatings exhibited early catastrophic failure due to insufficient bonding strength. Raman spectroscopy and wear morphology analyses confirmed that abrasive wear dominates tool degradation, with coarse-grained coatings enhancing durability by reducing non-diamond phases. This research provides a theoretical foundation for optimizing tool design and coating parameters in graphite mold machining, emphasizing the synergistic control of grain size and flute number to improve machining quality.