Abstract:The study focuses on micro-milling of a hardened tool steel with micro ball-end mills. The purpose is to observe the capability of a set of these mills to machine hard steels used for tooling applications. Different cutting configurations are here tested in order to evaluate their performance and finally enhance their design in this context. Experimental data, in terms of cutting forces, surfaces integrity and machining errors, is obtained from machining tests on a 40NiCrMo16 hardened steel with 0.5 mm diameter coated tungsten carbide micro-tools. The results allow highlighting some cutting, wear and dynamical phenomena related to the process. They are mainly associated to the types of mill and cutting conditions, as feed or tool/surface inclination. In this paper, the tool geometry and its dynamical behavior are mainly discussed.