Fibre metal laminates (FMLs) are multilayered metal composite materials currently used in aeronautical structures, especially where fatigue and impact resistance are required. FMLs are produced in large panels and often require assembly using the drilling process for riveting purposes. Hole making is a critical machining process in the joining and assembly of aeronautical components, which has to meet stringent tolerance requirements. This paper reports a systematic analysis of hole integrity when drilling an FML known as GLARE®. In particular, the primary objective is to investigate the impact of three different drill coatings (TiAlN, TiN and AlTiN/TiAlN), against several important hole parameters: thrust force, hole size, circularity, cylindricity and perpendicularity. The results show that TiAlN-coated drills produced the highest thrust force, while TiN-coated drills produced holes with the lowest deviation between the hole diameter measured at the entry and the exit and that the drill coating was the most influential parameter for the resulting hole size. TiAlN-coated drills resulted in the highest circularity at the upper part of the hole, while hole cylindricity tended to be best when using AlTiN/TiAlN- and TiN-coated drills. The ANOVA analysis shows that the drill coating and the spindle speed had a significant influence on hole size and circularity, while drill coating was the only influential parameter on hole cylindricity, and spindle speed was the only contributing parameter on hole perpendicularity. Finally, scanning electron microscopy analyses showed two distinct hole wall surface damage phenomenon due to broken fibres and evacuated metallic chips.

Fibre metal laminates (FMLs) are a special type of hybrid materials, which consist of sheets of metallic alloys and prepregs of composite layers stacked together in an alternating sequence and bonded together either mechanically using micro hooks or thermally using adhesive epoxies. The present paper contributes to the current literature by studying the effects of three types of cutting tool coatings namely TiAlN, AlTiN/TiAlN and TiN on the surface roughness and burr formation of holes drilled in an FML commercially known as GLARE®. While the cutting tool geometry is fixed, the study is also conducted for a range of drilling conditions by varying the spindle speed and the feed rate. The obtained results indicate that the spindle speed and the type of cutting tool coating had the most significant influence on the achieved surface roughness metrics, while tool coating had the most significant effect on burr height and burr root thickness. The most important outcome for practitioners is that the best results in terms of minimum roughness and burr formation were obtained for the TiN coated drills. However, such drills outperform the other two types of tools, i.e. with TiAlN and AlTiN/TiAlN coatings, only when used for short series of hole drilling due to rapid tool deterioration.