Ecofriendly inclined drilling of carbon fiber-reinforced polymers (CFRP)

Key composite made aerostructures such as fuselage inner walls, flap support fairings, empennage ribs, and the vertical fin ribs are comprised of non-vertical inclined and radial holes that join with other key metallic and non-metallic structures. Carbon fiber reinforced plastics (CFRP) are also used in the aerospace, automotive, marine, and sports-related applications due to their superior properties such as high strength to weight ratio, better fatigue, and high stiffness. CFRP drilling operation is different than the homogenous materials as the cutting-edge interacts with fiber and matrix simultaneously. Flank face of the tool rubs on the workpiece material and develops high frictional contact due to the elastic recovery of broken fibers. Lubrication during CFRP cutting can reduce the friction involved at tool-workpiece interface to enhance cutting performance. Dry cutting, cryogenic machining, and minimum quantity lubrication (MQL)-based strategies are termed as ecofriendly cooling/lubrication methods when machining high performance materials. The abrasive nature of carbon fiber is responsible of producing cutting forces which leads to different types of imperfections such as delamination, uncut fiber, fiber breakout, and fiber pullout. The integrity of CFRP drilled hole especially at the entry and exit of the hole plays a significant role towards the overall service life. The presented paper aims to characterize the interrelationships between hole inclination, lubrication/cooling methods, tool coating, and drill geometry with inclined hole bore surface quality and integrity during drilling of CFRP laminates. In dry cutting, thrust forces were found 2.38 times higher in the 30 degrees inclination when compared with the reference 90 degrees conventional inclination angle. Compressed air provided lowest increase (1.46 times) in the thrust forces for 30 degrees inclination.