Prediction and formation mechanism of serrated chips in cutting of SA508–3 steel under enhanced cooling and lubrication environments

The formation of serrated chips is the typical characteristic of high-speed machining. In this paper, a new prediction method based on Williams’ model was presented to give the critical cutting condition for serrated chips formation. The serrated chips formation mechanism under different cooling conditions was analyzed by finite element method. Results indicated that the cutting forces abruptly reduces when the serrated chip forms, the chips serrated degree (G_s) under various cooling conditions (i.e., dry, minimum quantity lubrication (MQL), supercritical CO₂ (scCO₂), and scCO₂-MQL) was described by the following order: scCO_2(Gs)＞scCO₂-MQL_(Gs)＞MQL_(Gs)＞dry_(Gs). The adiabatic shear owing to the cutting heat and crack initiated from the chip free surface under scCO₂ cooling promoted the serrated chips formation.