The effects of through tool cryogenic machining on the hole quality in GLARE® fibre metal laminates

GLARE® is a composite-metal laminate currently used in the Airbus A380 fuselage due to its excellent impact and fatigue performance. GLARE® undergo extensive drilling for riveting purposes making it prone to thermal effects and increased tool wear. Therefore, using coolants becomes necessary, however, conventional coolants can lead to moisture absorption. An alternative is to use cryogenic coolants due to their positive impact on machining aerospace materials in the past. In this study, through tool cryogenic machining technology is used for machining GLARE® laminates by delivering liquid nitrogen at −196 °C through the spindle allowing the coolant to be in direct and continuous contact with the cutting zone. The aim is to investigate the impact of drilling parameters and cryogenic cooling on surface roughness, hole size, circularity and hardness at hole entry and exit sides. In addition, microstructural evaluation using scanning electron microscopy. The results indicate that the cryogenic cooling improved hole surface finish and gave better hole size at the top, while it had no impact on hole circularity. The hardness was increased at the entry and exit sides of the hole compared to that observed in dry drilling tests while scanning electron microscopy revealed that burr formation was minimised.