A critical review addressing conventional twist drilling mechanisms and quality of CFRP/Ti stacks

CFRP/Ti stacks have attracted considerable attention over the past decades as a promising alternative to individual fibrous composites and metallic alloys due to their improved properties and enhanced structural functions. Mechanical drilling is a compulsory but challenging process to shape these compound stacks to desired dimensions and target quality. Despite a large volume of studies already addressing the conventional twist drilling of CFRP/Ti stacks, a comprehensive understanding of their fundamental drilling mechanisms is still lacking. The present paper aims to report the state-of-the-art advances achieved in the fields of CFRP/Ti machining. Aspects including chip removal, damage formation, mechanical/thermal effects, influences of process conditions, hole quality attributes, and tool wear mechanisms are carefully reviewed. An emphasis is placed on the discussion of the interface drilling behaviors as well as the impacts of different drilling sequence strategies on the machining outputs of CFRP/Ti stacks. The current research limitations and future research perspectives are pointed out. The review paper could provide technical guidance for both scientific and industrial communities to achieve the damage-free drilling of CFRP/Ti stacks.