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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...

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Carbon fiber-reinforced polymers (CFRP) are widely used in the aerospace industry. A new generation of aircraft is being built using CFRP for up to 50% of their total weight, to achieve higher performance. Exit delamination and surface integrity are significant challenges reported during conventional drilling. Exit delamination influences the mechanical properties of machined parts and, consequently, reduces fatigue life. Vibration-assisted drilling (VAD) has much potential to overcome these challenges. This study is aimed at investigating exit delamination and geometrical accuracy during VAD at both low- and high-frequency ranges. The kinematics of VAD are used to investigate the relationship between the input parameters (cutting speed, feed, vibration frequency, and amplitude) and the uncut chip thickness. Exit delamination and geometrical accuracy are then evaluated in terms of mechanical and thermal load. The results show a 31% reduction in cutting temperature, as well as a significant enhancement in exit delamination, by using the VAD technology.

In this paper, the tool wear mechanisms for low-frequency vibration-assisted drilling (LF-VAD) of carbon fiber-reinforced polymer (CFRP)/Ti6Al4V stacks are investigated at various machining parameters. Based on the kinematics analysis, the effect of vibration amplitude on the chip formation, uncut chip thickness, chip radian, and axial velocity are examined. Subsequently, the effect of LF-VAD on the cutting temperature, tool wear, delamination, and geometrical accuracy was evaluated for different vibration amplitudes. The LF-VAD with the utilization of minimum quantity lubricant (MQL) resulted in a successful drilling process of 50 holes, with a 63% reduction in the cutting temperature. For the rake face, LF-VAD reduced the adhered height of Ti6Al4V by 80% at the low cutting speed and reduced the crater depth by 33% at the high cutting speed. On the other hand, LF-VAD reduced the flank wear land by 53%. Furthermore, LF-VAD showed a significant enhancement on the CFRP delamination, geometrical accuracy, and burr formation.

Objective: The objective of this study was to evaluate the effect of different pH media on color stability, translucency and surface roughness on Hybrid ceramic material (Vita Enamic) and bilayered reinforced polymer (PEEK). Materials and methods: A total of 60 discs, 30 in each group that were designed with milled with CAD/CAM, each group was further subdivided into 3 subgroups (10 samples in each group) according to the immersing solution.(neutral, weak acid and strong acid), all samples were aged in the immersion solutions for 24 days in an incubator at 37 o which simulate 2 years of clinical service. Optical profilometer was used to assess surface roughness, a spectrophotometer was used to assess color change and translucency was calculated with the tranclucency parameter equation. Results: The results showed that no statistical significant difference in surface roughness, color stability and translucency with Vita Enamic in different solutions, and statistical significant difference with PEEK group in different solutions. Conclusion: Vita Enamic has higher color stability and translucency than PEEK and can maintain smoother surface with different pH media.