Investigation of delamination in stack drilling of carbon fiber reinforced composites

Fiber reinforced composite materials are mostly preferred in aerospace, aviation and automotive industries. These materials are subjected to drilling operations in order to make bolt and riveted joints between each other. Improper parameter selection causes undesirable conditions such as thermal damage to the hole surface, push-down delamination and fiber breakage when a drill comes out of the laminate. In this study, the stack drilling of carbon fiber-reinforced polymer (CFRP) composites was experimentally investigated in terms of entry and exit damage, point angle, helix angle, cutting speed, and feed rate. In this study, the Al6013/KETPK/Al6013 stacked structure was drilled with uncoated HSS drills with 90° and 118° point angles and 15° and 22.5° helix angles. 0,05; 0,1; 0,2 mm/rev feed rate, 45, 67, 100 m/min cutting speed parameters were used. The hole entry and exit delaminations were investigated according to the drilling results. As a result of the experimental study, delamination decreased with increasing cutting speed decreases and decreased feed rate. In the experiments, it was observed that the hole entrance damage was higher than the hole exit damage. Moreover, it was observed that the delamination rate was less at large point angle and large helix angle. In this study, the lowest delamination ratio was acquired at the highest cutting speed (100 m/min) and the lowest feed rate (0,05 mm/rev) with the drill which had 118° point angle and 22,5° helix angle.