The constant industrial need of detail data on the chip formation meets with the lack of a physical understanding of the thermo-mechanical couplings during hard metal cutting. In the present paper, numerical and experimental investigations at micro scale (about 0.5 × 0.5 mm2 area), is performed in order to highlight the mechanisms responsible for the poor Ti-6Al-4V machinability. In a first step, strain, strain-rates, temperatures, dissipated powers along with displacements, velocity and crack propagation are obtained at each pixel by means of VISIR apparatus. Experimental observations have highlighted the dependency of the physical phenomena to both cutting speed and rake angle and provide valuable evidences on the different nature of the coupling phenomenon. Secondly, a 3D FE orthogonal cutting model is then developed to bring a multi-scale comprehension of Ti-6Al-4V chip genesis and to predict the kinematics and thermal quantities. The numerical and experimental confrontation revealed the robustness of the developed FE model as well as its limits. Hence, the element deletion method and the friction model are identified as the main weak spots of the proposed FE model. Finally, a particular attention is paid to the chip formation steps and their impact on the final part.