Investigation of Delamination and Cutting Force in the Drilling of AA7050-CFRP Hybrid Composite Stacks Used in Real Aerospace Applications

This study investigates the combined effects of drilling parameters and tool features on thrust force during drilling of hybrid AA7050/CFRP stacks intended for aerospace applications. Experiments were designed using a Taguchi L16 (4222) orthogonal array by considering feed rate, cutting speed, drill diameter, and coating condition. Unlike most previous studies on Al/CFRP stack drilling, this work provides a layer-specific evaluation by separately analyzing the thrust-force responses of the AA7050 and CFRP layers, while also correlating force behavior with aluminum-side damage and CFRP-side delamination within a unified framework. For the aluminum layer, feed rate was the dominant factor affecting thrust force, with a contribution of 71.22%, followed by drill diameter (26.22%). For the CFRP layer, drill diameter was the most influential parameter (52.58%), followed by feed rate (43.77%). Thrust force ranged from 155.24 to 414.45 N for AA7050 and from 77.73 to 175.39 N for CFRP. Uncoated tools and higher feed rates increased thrust force, leading to poorer machining performance. Delamination in the CFRP layer was primarily governed by feed rate (46.71%), followed by drill diameter (35%). Overall, increasing feed rate and drill diameter significantly deteriorated the machinability of the hybrid structure.