Multi-spindle drilling of Al2024 alloy and the effect of TiAlN and TiSiN-coated carbide drills for productivity improvement

High precision drilling is required to ensure the structural integrity of the aircraft. Therefore, strict quality controls are required to ensure optimum hole quality since hundreds of thousands of holes are drilled into different aircraft structures. The large number of holes required for riveting means that their installation must be carried out in a fast and precise manner. This can be achieved using multi-head drilling tools that can drill several holes simultaneously. The current study investigated the use of a multi-spindle drill head that can produce three holes simultaneously. Uncoated carbide and TiAlN- and TiSiN- coated carbide drills were used to assess cutting forces, hole surface roughness, burr formations and tool condition when machining Al2024 aerospace alloy under dry machining conditions. Analysis of variance was employed for estimating the relationships between the input parameters (spindle speed, feed and tool coating) and the studied hole quality metrics. Further, a regression model was developed with a regression coefficient (R²) of more than 90% for the prediction of measured responses. Interestingly, better results in lower thrust force and surface roughness were obtained using the uncoated carbide drills compared with TiAlN and TiSiN. While the performance of TiAlN was found to be better than those obtained from TiSiN.