A Comparative Assessment of Hole Integrity with Twist Drill Geometry in Drilling AFRP/AL7075-T6 Stack Material

Drilling Aramid Fiber Reinforced Plastic (AFRP) with aluminium (AL7075-T6) is challenging. It is crucial to maintain the dimensional accuracy and minimize burr formation. In this study, two carbide drill bit were tested across 13 runs with varying combinations of feed rates (0.05, 0.08, 0.10 mm/rev) and spindle speeds (2000, 4000, 6000 rev/min), using a central composite design (CCD) methodology within the Design of Experiment (DOE) framework. The drill geometries included angles such as the helix angle, primary clearance angle, chisel edge angle, and point angle. For the tapered web drill bit, angles were set at 10º, 6º, 45º, and 130º, while for the burnishing drill bit, they were 20º, 8º, 30º, and 135º, respectively. The primary focus of the experiment was to assess hole quality, specifically evaluating hole diameter error and burr height formation. Among the 13 runs conducted, the tapered web drill bit exhibited superior performance in terms of hole diameter error, showing a deviation of-0.5 µm in Run 8, compared to a deviation of 1.2 µm for the burnishing drill bit in Run 12. Additionally, the tapered web drill bit demonstrated a lower burr height of 63.97 µm in Run 12, while the burnishing drill bit resulted in a burr height of 95.44 µm in Run 4. These findings enhance aircraft production by promoting better hole quality with optimal drill bits, leading to material savings, lower rejection rates and cost reduction, thus boosting reliability and productivity.