Tool wear of advanced coated tools in drilling of CFRP

This paper aims to investigate the effectiveness of super-hard ceramic coatings by evaluating tool wear when drilling carbon fiber-reinforced plastics (CFRP) composite. The drilling experiments of CFRP are conducted with diamond-like carbon (DLC) coated, AlMgB14 (BAM) coated, AlCrN and Si3N4 and TiN (simply denoted as (AlCrSi/Ti)N) coated, and uncoated tungsten carbide drills. Each coating, dictated by its unique processing technique, provides unique thickness and morphology, and its physical properties, which makes the comparison among the coatings much difficult but enables to deduce the desirable attributes in the prospective coating ideally suited in drilling CFRP. To do so, after the drilling experiments, the tool wear was captured using the scanning electron and confocal laser scanning microscopes to construct the wear evolution that enables us to evaluate each coating qualitatively as well as quantitatively. Among the drills tested, the (AlCrSi/Ti)N-coated drills provided the best performance despite of the fact that (AlCrSi/Ti)N coating particularly are not harder than any other coating. The superior performance of the (AlCrSi/Ti)N coating can be explained by the comparable stiffness to the carbide substrate, 7.3 μm-thick coating consisting of the numerous nanoscale alternating layers between nanocomposite of AlCrN and Si3N4 and TiN coatings and the enhanced adhesion, which provide the effective cutting of carbon fibers. However, the thin DLC coating despite of its superior hardness and the BAM coating despite of its low friction did not perform at the level that the (AlCrSi/Ti)N coating was able to achieve.