Trade-Off for CFRP Quality Using High-Frequency Ultrasonic-Assisted Drilling Under Lubricant Absence

Carbon fiber reinforced polymers (CFRPs) are significantly vital for industries. However, the drilling process of a CFRP is considered a challenge due to its nature, which causes delamination, fiber pull-out, peel-up, high friction, and a decrease in cutting tool life. Wet drilling is necessary for minimizing defects, and lubricants are very costly. In the current work, ultrasonic-assisted drilling (UAD) with a longitudinal vibration of 39.7 kHz was applied to the drill bit in the feed direction, used for CFRPs, and compared with conventional drilling (CD). Low spindle speeds under 5000 rpm were applied with different feed rates. The morphology, delamination factor, and cutting forces were investigated through the specific input machining parameters for CD and UAD. SEM was applied to study the morphology of the hole entrance and exit as well as the burr heights of evacuated chips. UAD with 39.7 kHz succeeded in minimizing the surface roughness by 50% compared with the surface roughness resulting from CD and could drill high-precision holes for CFRPs with a trade-off concept, besides achieving near-zero delamination (K ≃ 1) in the absence of a lubricant, which is being extended for industrial application.