Extracting information from the cutting force signal to explain and exploit its discrepancy between up and down slot milling at the same chip thickness

Abstract

In milling, different cutting forces can occur at the same undeformed chip thickness depending on process kinematics and feed. To clarify and exploit this phenomenon, which has not been reported in the technical literature, the cutting force was recorded during full-width orthogonal milling. The latter process was chosen as the same undeformed chip thickness is developed at certain tool rotation angles and at different feeds, thus allowing the exploration of the effect of these parameters on the cutting force. Using analytical methods to describe the cutting kinematics, the exact rotation angle of the tool corresponding to its engagement with the workpiece was calculated. In addition, the precise relationship between chip thickness and occurring cutting force in up and down slot milling at various feeds was determined. Herein, for increasing the accuracy, the tool path was considered as trochoidal rather than circular. In addition, analytical methods were developed to calculate the cutting force direction, shear angle and chip compression ratio. The measurements of the deformed chip thickness over the deformed chip length verified the assumptions and correctness of the developed analytical procedures. Additionally, based on a FEM simulation of the developed stress fields during material removal, the stress field depth parameter ds was introduced. Using ds and the calculated direction of the cutting force towards the instantaneous workpiece surface, regions of effective material strengthening or weakening were detected within the developing stress field during up and down milling respectively, which change the cutting force. In this way, the discrepancies between the cutting forces occurring in up and down milling at the same undeformed chip thickness and various feeds were clarified and process conditions were proposed to exploit them to reduce cutting loads and energy requirements.