Improvement of drilling performance by overcoating diamond-like carbon films on diamond-coated drills for carbon fiber reinforced plastics processing

The hardness and hydrogen content of diamond-like carbon (DLC) films vary depending on the film deposition methods and conditions. Carbon fiber reinforced plastics (CFRP), known as hard-to-machine materials, have been widely used for industrial aircrafts that require structural materials. In this study, the effects of the hardness and hydrogen content in DLC films on the drilling performance of CFRP drills were investigated. Various DLC films, prepared using the T-shaped filtered arc deposition method, were used to coat diamond-coated drills for CFRP processing. The drilling test of the CFRP plates revealed that the occurrence of burrs was suppressed using the drill coated with a hard DLC film containing small amounts of hydrogen, classified as a hydrogenated tetrahedral amorphous carbon (ta-C:H) film. The spherical polishing test of the CFRP plate using DLC-coated balls demonstrated that the DLC films containing hydrogen suppressed the adhesion of the resin material constituting the CFRP. The coating of hard DLC films containing small amounts of hydrogen, such as a ta-C:H film, significantly improved the drilling performance of diamond-coated drills for CFRP processing. The performance improvement of CFRP drills expands the range of CFRP processing conditions.