An experimental assessment and optimisation of hole quality in Al2024-T3 aluminium alloy during abrasive water jet machining

Owing to its outstanding properties such as corrosion resistance, low density, relatively low cost, and stiffness, Al2024-T3 aluminium alloy has been widely applied in aircraft manufacturing. To perfectly assemble an aircraft, numerous high-quality holes are drilled into its structures employing conventional drilling processes. Conventional drilling poses some challenges such as thermal distortions, burr formations, and tool wear. Alternatively, abrasive water jet drilling (AWJD) is a thermal-free machining process that can be employed as an alternative to conventional drilling of aeronautical structures. Hence, in this work, the effect of abrasive water jet parameters, namely stand-off distance, water jet pressure, and abrasive mass flow rate, on hole-quality parameters was evaluated at traverse speed = 10 mm/min. Three parameters were stand-off distance = 1, 2, and 3 mm, abrasive mass flow rate = 200, 250, and 300 g/min, and water jet pressure = 1800, 2100, and 2600 bar. Using a 6 mm circular-movement diameter of the nozzle tip, optimal stand-off distance, water jet pressure, and abrasive mass flow rate obtained by multi-objective optimization were 2 mm, 250 g/min, and 2600 bar, respectively. The corresponding hole-quality parameters were Diameter = 6.232 mm, Kerf angle = 0.018°, Cylindricity = 0.051 mm, Perpendicularity = 0.033 mm, Circularity = 0.0041 mm and Surface roughness R_a = 2.909 µm. The results showed that water jet pressure had the greatest influence on Perpendicularity, Circularity; stand-off distance had the highest effect on Kerf angle; and abrasive mass flow rate has the largest influence on Hole diameter, Cylindricity and Surface roughness R_a, and R_z at the given value of traverse speed. The adopted optimization process for abrasive water jet of Al2024-T3 aluminium alloy was successfully verified through confirmation runs, clearly illustrating its benefits.