Cryogenic drilling of carbon fibre reinforced plastic with tool consideration

The use of carbon fibre reinforced plastic (CFRP) components has seen a significant increase over the last decade in the aerospace and automotive industry. Such components require holes to facilitate the use of mechanical fasteners, and the need to drill them at the point of assembly is a common requirement. To reduce the scrappage of high value parts during the final manufacturing stages, there is an industry requirement to improve strategies for drilling CFRP. Cryogenic cooling has shown promising improvements in terms of tool life and part quality in drilling CFRP. However, there are limited studies on the combination of tool geometry and cryogenic machining for CFRP. In this preliminary study, two new drill geometries namely, spur and step drills are investigated using external nozzle cryogenic cooling with liquid nitrogen and dry machining environments. The analysis indicated that cryogenic cooling in combination with spur drills can improve machinability in drilling CFRP. This investigation revealed that using cryogenic cooling can reduce delamination at the exit and improve surface roughness by 25% as well as surface integrity in drilling CFRP. Whilst the best surface roughness and lowest delamination was attributed to the cryogenic machining with spur drill, dry machining environment performed best when using step drill. This indicates the dependency of the machining environments to the cutting tool geometry.