Hard machining under dry conditions with hard PVD coatings on cemented carbide endmills

Machining of hardened steel needs cutting tools for extreme conditions. Not only the cemented carbide tool material, but also the hard or ultra hard coating determines the tool life and cutting performance on the work piece. For milling operation in hardened material 1.2379 with a hardness between 60 and 62 HRc, endmills coated with different TiAlN layers in single or multilayer design and also top coatings with friction performance are used. Cutting tests with investigations of the wear on the cutting edge and in situ infrared temperature measurements by video camera showed large differences in tool performance. According to these results the limitation of cutting time or cutting length is, in some cases, not only caused by the wear on the tool, but also by the surface temperature of the work piece material. (author)