Fabrication, tribological properties and cutting performances of high-quality multilayer graded MCD/NCD/UNCD coated PCB end mills

Abstract

Ultrananocrystalline diamond (UNCD) coating possessing low surface roughness was innovatively deposited on printed circuit board (PCB) end mills in order to improve the surface smoothness and prolong the tool duration while machining 5G PCB material. Six types of diamond coatings, involving microcrystalline diamond (MCD), nanocrystalline diamond (NCD), ultrananocrystalline diamond (UNCD), microcrystalline diamond/nanocrystalline diamond (MCD/NCD), microcrystalline diamond/ultrananocrystalline diamond (MCD/UNCD), microcrystalline diamond/nanocrystalline diamond/ultrananocrystalline diamond (MCD/NCD/UNCD), were synthesized on PCB end mills. The Raman spectrum of diamond coatings were obtained to characterize the phase composition, illustrating that Raman spectra of UNCD, MCD/UNCD and MCD/NCD/UNCD present “M” shape, including dominant D peak and G peak. The adhesion levels were assessed, showing that the bottom MCD layer helps to improve the adhesion of MCD/NCD, MCD/UNCD and MCD/NCD/UNCD on WC-Co substrates and MCD/NCD/UNCD can suppress effectively the crack propagation. Moreover, the tribological properties and wear performances of these diamond coatings were compared. The comparison results of friction coefficients are in good accordance with those of surface roughness. The superior adhesion of bottom MCD, the elegant transition of middle NCD and the low friction coefficient of the top UNCD lead to the outstanding wear performances of MCD/NCD/UNCD coated end mill while machining PCB slots.