Evaluation of force variations mechanisms during radial immersion micromilling

Micromilling outcomes are significantly affected by a condition of the machine-tool system, as well as the selection of milling inputs. In this context, many studies have been conducted on the evaluation of physical phenomena and technological effects of micromilling. However, the identification of a cutting force variations mechanisms and their effect on a machined surface formation still constitutes a research gap. Therefore, this study focuses on an in-depth evaluation of cutting force variations mechanisms during radial immersion micromilling and their effect on a formation of a machined surface topography. The carried out research involves both the experimental trials, as well as the analytical modeling. In the first stage, a micromilling force model, concerning a distribution of elemental forces along the main and secondary cutting edges, as well as the rounded tool corner has been proposed. This model assumed that directions of the cutting force components are dependent on their point of application and included a calculations of a specific cutting force coefficients, tool run-out and geometrical parameters of cut on the basis of the area of cut determined concerning a continuous consideration of the process kinematics. In the next part an evaluation of cutting force variations in terms of tool rotation angle, variable radial immersion, and tool helix angle has been presented. The generated modeled quantities were further validated experimentally on the ultra-precision 3-axis machine tool, involving a micromilling experiments on the Inconel 718 superalloy. The experiments included the measurements of cutting forces on the 3-axis piezoelectric dynamometer, as well as the machined surface topographies on the laser interferometer. Results have shown that during down-milling conditions, a substantial variations of feed and thrust forces were found. These variations manifested as abrupt changes in force signs, as a function of tool rotation angle and radial depth of cut. Moreover, based on the conducted experiments, it was found that machined surface topographies reveal some areas in which an elevated surface irregularities are present, in comparison to ones appearing in the remaining zones. It was observed that a presence of these elevated irregularity bands is strictly correlated with an appearance of a thrust force variations during tool input. • Novel cutting force model including force distribution along the helical cutting edge • Three distinct cutting force variability areas during the CWE process • Effect of process kinematics, tool geometry on shape and value of force variations • Role of axial force variations on formation of a machined surface anomalies