Hole surface morphology and tool wear mechanisms during cutting 3D carbon/carbon composites using diamond core drill

Abstract

Carbon fiber reinforced carbon matrix (carbon/carbon) composites are a new class of ceramic engineering materials and applied in aerospace structures due to high strength in non-oxidizing atmospheres at extremely high temperatures, while it is a typical difficult-to-machine material due to its anisotropy and heterogeneity. Defects such as burrs, tears and fiber pullout are likely to be produced on machined surface when inappropriate machining parameters are employed. The material removal mechanisms during mechanical cutting of carbon/carbon composites are still not fully understood. In this work, the three-dimensional braided carbon/carbon composite was employed, hole surface morphology and tool wear mechanisms during drilling with a bronze sintered diamond core tool were studied. Result showed that fiber tearing and burrs were mainly observed at hole entrance and exit under low level of feed speed down to 20 mm/min. When the feed speed increased to 40 mm/min and 60 mm/min, severe tearing, uncut fibers, and delamination appeared at hole exit. Fiber orientation showed significant influence on material removal mechanisms as well as fiber shearing/bending fracture, fiber pullout and matrix fragmentation. The ground, pullout and fracture of abrasive particles were the main tool wear mechanisms, cutting chips were attached and blocked inside the core drill probably due to high cutting temperature in dry condition, as the temperature increased to ∼260 °C under the feed speed of 60 mm/min.