Elimination of delamination and burr formation using high-frequency vibration-assisted drilling of hybrid CFRP/Ti6Al4V stacked material

The superior physical and mechanical characteristics of CFRP/Ti6Al4V stacked structures explain their widespread use in the aerospace industry. However, the unacceptable machining-induced tensile surface residual stresses and reduced surface integrity are the main challenges that are faced in the conventional drilling process. These types of damage are attributed to the relatively high thermal load and poor chip evacuation mechanism. Vibration-assisted drilling is a promising technique to control the uncut chip thickness, and consequently reducing the cutting energy. Moreover, the axial tool oscillation provides a mechanism for effective chip evacuation. This study presents an experimental investigation relating the high-frequency vibration-assisted drilling (HF-VAD) machining parameters to the Ti6Al4V burr formation and induced residual stresses, as well as CFRP delamination during the drilling of CFRP/Ti6Al4V staked material. Additionally, this study presents an assessment and comparison between HF-VAD and LF-VAD of CFRP/Ti6Al4V hybrid structure. The results showed up to approximately 26%, 37%, and 86% reduction in the thrust force, cutting temperature, and the exit burr height, respectively. The effect of HF-VAD on surface integrity and Ti6Al4V residual stresses are also presented. The drilling process of HF-VAD resulted in free exit delamination of CFRP with compressive residual stress on the Ti6Al4V machined surface.