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Cutting tool performance is mainly characterized by material substrate, cutting edge geometry and coating, and also by a good choice of the cutting parameters, mainly cutting speed, depth of cut and feed. In drilling a good choice of substrate/coating can reduce production costs per hole cut by 50%. Coatings evolution has gone from monolayer to nanostructured and/or nanometric-scale multilayer coatings. These are used because of their high hardness, and good corrosion and oxidation resistance and thermal stability. Cutting edge preparation on one hand and droplet elimination after the coating process in the other are important issues for reaching a good tool/coating performance, being a key issue.In this article a series of coatings for drilling low and medium carbon alloyed steels are presented, along with their performance. Validation tests were carried out on steel 42CrMo4, very used in the automotive sector. Seven coatings were tested, including AlCrSiN, μAlTiN, TiAlCrN, AlTiCrN, AlCrN, AlTiSiN and TiAlSiN. Flank wear, evolution of drilling thrust force and torque, damage on cutting edge faces on primary cutting edge and behaviour of drill bit secondary edges were studied. A final elimination Downloaded by [134.of droplets by drag grinding was performed in several cases. Process monitoring, SEM microscopy and EDX analysis were used, concluding that the best results were for μAlTiN, TiAlSiN and AlTiSiN. Reasons for the good behaviour are the good surface finishing after droplet elimination and the high thermal stability of these protective layers.

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