Evaluating the impact of boundary conditions and clamping force in robotic one-up drilling of hybrid stacks

The rapid increase in air traffic and the growing focus on more sustainable solutions require improvements in fuel efficiency and cost reduction, highlighting the importance of lightweight materials in aircraft manufacturing. This study investigates the one-up drilling process of Carbon Fibre Reinforced Polymer and AA7075-T6 stack, focusing on the influence of process parameters, drilling boundary conditions and clamping force on the hole quality. A robotic drilling system was used to study both ideal and non-ideal boundary conditions. Under ideal boundary conditions, optimal drilling parameters were identified: a cutting speed of 85 m/min and a feed rate of 0.01 mm/rev for CFRP, and 60 m/min with 0.05 mm/rev for AA7075-T6. Therefore, parameter switching strategies were implemented to improve hole quality at the material transition zone. Then, under non-ideal boundary condition, variable clamping forces (0 N, 250 N, and 400 N) were applied by the robot's end effector, demonstrating that higher clamping forces significantly reduce interlayer gaps, leading to up to 60.27 % reduction in entry burr and 16.10 % decrease in delamination factor. This comprehensive approach provides deeper understanding on how process parameters and boundary conditions affect both hole quality and tool forces, offering new insights for optimising drilling processes in aerospace manufacturing.