On the influence of clamping conditions and cutting edge geometry on drilling of thin aluminium stacks

This study investigates the semi-automatic drilling of thin AA2024-T3/AA7075-T6 aluminium stacks, aiming to address the challenges posed by their reduced flexural stiffness. The novelty of the research lies in evaluating the combined influence of cutting edge and clamping conditions (i.e. with and without the use of a backup plate) on hole quality and drilling forces. Drilling tests were performed using three tools with different cutting edge angles (120°, 140°, and 160°) across nine combinations of cutting speed and feed rate. The findings identify two distinct deformation mechanisms that govern hole quality: localized plastic deformation under supported conditions and global flexural deformation when the stack is unsupported. Contrary to expectations, the use of a backup plate does not always improve hole quality; in some cases, it induces stress concentrations that exacerbate burr formation. For instance, the burr height increased by up to 121.6 % in unsupported conditions using a 120° tool, due to pronounced elastic recovery during drilling. In contrast, the burr height decreased by up to 55.5 % when using a 160° tool under the same unsupported conditions. Finally, in both conditions, the deformation mechanisms negatively affect the dimensional accuracy of the hole due to uneven material displacement and dynamic variations in tool–material interaction. The results of this study highlight how clamping conditions and tool geometry can significantly influence the drilling process and hole quality, shedding light on phenomena and aspects that must be considered when drilling thin-walled aerospace components, especially in scenarios where rigid support cannot always be guaranteed.