Effects of laser power, assist-gas pressure, and feed rate on HAZ and hole quality in CO2 laser drilling of 5052 aluminum–glass fiber metal laminates

Fiber–metal laminates (FMLs) combine the lightweight characteristics of fiber-reinforced composites with the strength and damage tolerance of metallic layers, but producing high-quality holes remains challenging because of their heterogeneous structure. In this study, continuous-wave CO 2 laser drilling of a laboratory-fabricated 5052 aluminum–glass fiber metal laminate was investigated using a randomized three-factor, three-level full-factorial design. Laser power, assist-gas pressure, and feed rate were varied at 2.5–3.5 kW, 6–10 bar, and 6600–8600 mm/min, respectively. The 27 treatment combinations were each replicated on three independently drilled holes, resulting in 81 observations. Hole quality was evaluated in terms of heat-affected-zone (HAZ) width, absolute hole-diameter deviation from the nominal 6.00 mm diameter, and deviation of the hole-wall angle from the ideal 90° geometry. Full-factorial ANOVA showed that laser power was the dominant factor affecting HAZ width, while feed rate and the laser-power × assist-gas-pressure interaction were also significant. Hole-diameter accuracy exhibited the strongest interaction structure, with the three-way interaction among laser power, assist-gas pressure, and feed rate accounting for approximately 30.2% of the total variation (p<0.001). For hole-wall geometry, signed taper deviation was used for factorial inference to preserve the direction of deviation from 90°, whereas absolute taper deviation was used for multi-response evaluation. Laser power was the dominant factor affecting signed taper deviation, with a significant laser-power × assist-gas-pressure interaction. HAZ width showed a non-monotonic dependence on laser power, increasing from 2.5 – 3.0 kW and decreasing at 3.5 kW. Multi-response evaluation identified 6 bar assist-gas pressure, 2.5 kW laser power, and 7600 mm/min feed rate as the best balanced condition among the experimentally evaluated combinations, yielding mean HAZ width of 0.255 mm, diameter deviation of 0.020 mm, and absolute taper deviation of 0.797°. The results demonstrate that reliable control of CO 2 -laser-drilled FML hole quality requires simultaneous consideration of thermal damage, dimensional accuracy, and interactions among the processing parameters.