Monitoring Shearing-Plowing Transitions in Micro-Milling Using Fluctuations in Cutting Forces

Abstract

Abstract In micromilling, understanding transitions between the desired shearing-dominant to the undesired plowing-dominant cutting mechanism could help obtain high quality microfeatures. This work investigates the transitions in cutting mechanisms in micromilling using fluctuations in cutting force signals, characterized by using a fluctuation parameter. A new analytical model correlating fluctuation in force signals to the transitions in cutting mechanism has been developed. Two types of slot milling experiments were performed to understand the transitions in cutting mechanisms, as a function of processing parameters, and over the entire life of micro-endmills. The proposed model was found to agree with experimental values of forces within 15% error. The limiting value of the fluctuation parameter has been estimated as 0.01, which corresponds to a limiting feed of 1 μm/tooth. Feed per tooth and cutting edge radius are the important parameters that affect transitions in cutting mechanisms. The cutting mechanism changes from shearing to plowing and vice-versa over the entire life of the tool. Shearing-dominant mechanism prevailed in the first region due to the sharper cutting edges with radius less than 9 μm. Though plowing-dominant cutting mechanism prevails in the remaining two regions, the mechanism comes closer to shearing-dominant near the end of tool life. This is primarily because of the generation of localized sharpness on tool cutting edges due to chipping. Furthermore, it was evident that cutting mechanism changes from shearing to plowing due to wear, when surface roughness increases above 400 nm Ra.