Influences of TiAlN coating and limiting angles of flutes on prediction of cutting forces and dynamic stability in micro milling of die steel (P-20)

Due to a lower stiffness value, the micro tool is prone to deflection that ultimately gives rise to chatter, tool wear, catastrophic tool breakage and worse surface generation. Especially, during micro milling of hard materials, these issues become more critical. To encounter these impediments, a hard coating with lower coefficient of friction of the cutting tool can be regarded as a viable solution to improve its tooling performance by reducing the tool wear and tool breakage. However, the prediction of cutting forces and stability limits, considered essential to enhance the tooling performance in micro milling using coated tool, has not been reported so far. This article proposes an analytical approach for the prediction of cutting forces in both shearing and ploughing dominant regions by combining FEM simulation and mechanistic modelling by the consideration of tool run out, minimum chip thickness (MCT), elastic recovery, ploughing area and limiting angle (entry and exit angles) of the flutes for the combination of TiAIN coated tool and P-20 steel workpiece. Furthermore, the modelling of dynamic stability in frequency domain has been instituted by incorporating the force coefficient obtained from FEM simulation results and the exact entry and exit angles of the flutes which change due to tool run out. Finally, both proposed models have been verified through experimental results, and the influence of coating material has been shown to be viable by enhancing the stability limits and by reducing the prediction error of cutting forces.