The use of lightweight material such as CFRP/Ti6Al4V in stacked structures in the aerospace industry is associated with improved physical and mechanical characteristics. The drilling process of nonuniform structures plays a significant role prior to the assembly operation. However, this drilling process is typically associated with unacceptable CFRP delamination, hole accuracy, and high tool wear. These machining difficulties are attributed to high thermal load and poor chip evacuation mechanism. Low-frequency vibration-assisted drilling (LF-VAD) is an advanced manufacturing technique where the dynamic change of the uncut chip thickness is used to manipulate the cutting energy. An efficient chip evacuation mechanism was achieved through axial tool oscillation. This study investigates the effect of vibration-assisted drilling machining parameters on tool wear mechanisms. The paper also presents the effect of tool wear progression on drilled hole quality. Hole quality is described by CFRP entry and exit delamination and hole accuracy. The results showed a significant reduction in the thrust force, cutting torque, cutting temperature, and flank wear-land.This wear mechanism was attributed to hard and soft abrasion modes [14]. The hard mode is located at WC grains due to the generated dynamic stresses from the broken fiber, material reinforcement, and powder like chips [15]. Consequently, the WC grains suffer crack initiation and propagation fracture [16]. On the other hand, the relatively low hardness Co binder is more easily damaged by carbon fibers (CF) in a process known as soft abrasion mode [14,17,18]. Hence, WC grain spalling is more rapid under the cyclic machining load.High cutting temperature, poor chip evacuation mechanism, and burr formation are of the common issue during the drilling process of Ti6Al4V [19][20][21]. These problems resulted in a higher probability of flute-chip accumulation, progressive tool wear, and poor surface integrity [19,20,22]. Low thermal conductivity and high chemical affinity to the majority of tool materials are due to the adverse titanium characteristics, which resulted in a significant reduction in the tool life with a high probability of catastrophic failure [20,23,24]. This effect contributed to the cutting stress concentration on the tool cutting edge where the maximum cutting temperature is located. Therefore, the machining process of Ti6Al4V is typically associated with the formation of built-up-edge (BUE). The formation of BUE has a significant drawback on the machined surface integrity and the tool life [25,26]. Thus, adding more limitations in the aerospace production procedure [27].Despite, the extensive to optimize separate machining process of both materials, the machining process suffers when it comes to production time, cost, and assembly positional error. Single process drilling of the CFRP and Ti6Al4V materials in situ, also known as stacked drilling shows considerable benefits to overcome separate drilling issues [1][2][3]28,29]. However, the stack drilling o...
