Effects of machining conditions on the hole wall delamination in both conventional and ultrasonic-assisted CFRP drilling

The need of carbon fiber–reinforced plastics (CFRP) has been driven by the increasingly wide applications in many industrials including sports, transportation, and energy. However, until now, the poor machinability of CFRP can be still considered the key problem and the most urgent machining-induced issue can be the delamination damage in the drilling process. Although many efforts have been paid to investigate this topic, most of them investigated the delamination at either the hole entrance and the exit. Very few of these studies focused on the internal delamination defects on the hole wall, although these internal defects can be as important as the entrance and exit defects. To fill this gap, this paper investigated the condition effects (feed rate, spindle speed, ultrasonic vibration of drills, and the workpiece support strategy) on the delamination in CFRP drilling, with the special focus on the internal delamination damage on the inside hole walls. Based on both the experimental and theoretical analysis, the effectiveness of the back supports and the variable feed rates was investigated as well. Considering few published studies reported the delamination on the hole wall, the key findings in this paper are expected to be meaningful to deepen the understanding of CFRP drilling and helpful to provide some industrial guidance.