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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.

This paper aims to investigate the effectiveness of several superhard ceramic coatings on carbide drills when drilling carbon fiber reinforced plastics (CFRP) composite/Ti-6Al-4V alloy (titanium or Ti) stacks. The drilling experiments of CFRP/Ti stack are conducted with diamond-like coating (DLC) coated, alternating layers of the nanocomposite of AlCrN & Si3N4 and TiN or (AlCrSi/Ti)N coated, and uncoated tungsten carbide drills. Tool wear evolution of each drill is measured qualitatively as well as quantitatively using the scanning electron and confocal laser scanning microscopes (CLSM) by interrupting after making certain numbers of hole. Based on our drilling experiments, the performance of each coating when drilling CFRP/Ti stack are discussed. Among these coated and uncoated drills, uncoated and DLC coated drills failed before making 5 holes while (AlCrSi/Ti)N coated drills performed the best making more than 80 holes. The DLC coating, despite of high hardness of DLC coating, does not provide any significant protection especially when drilling Ti layer.

Improving the machinability of titanium (Ti) alloys remains unresolved for manufacturing industries because excessive tool wear and catastrophic tool failures lead to shortened tool life and low productivity with any available cutting tool system. Besides optimizing the substrate and/or coating materials for cutting tools, improving the cooling and lubricating conditions is one of the ways to improve the machinability of Ti alloys. In this paper, we explore the possibility of using a nano-platelet, lamellar-type solid lubricant of graphite Exfoliated graphite nano-platelets (xGnP®) grade C750 (or xGnP750) in Minimum Quantity Lubrication (MQL) machining of Ti-6Al-4V (Ti64). Due to the lamellar or layered crystal structure, each layer easily slides against adjacent layers to provide the lubricity when introduced at the tool/work material interface. Although the nano-platelets have a nano-thickness, they have a micro-sized diameter, which prevents the nano-platelets from penetrating through human skin and breathing through nose. This makes the great advantage in this approach compared to other nano-enhanced MQL processes. The milling experiment shows that the nano-platelets present in the MQL oil decreased flank wear and improved the tool life compared to traditional MQL with pure oil as well as dry machining. The presence of nano-platelets reduces the micro chipping and tool fracture caused by the effect of impact in interrupted machining.

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