Estimation of minimum chip thickness for multi-phase steel using acoustic emission signals

Abstract

The determination of minimum chip thickness is important for establishing the lower limit of the feasible process window in micro mechanical machining for a given tool and workpiece material. The minimum chip thickness is encountered in micro milling operations owing to the variation in chip load as predicted by the chip density function. This study proposes a methodology to determine the value of minimum chip thickness by analysing acoustic emission (AE) signals generated in orthogonal machining experiments conducted in micro milling. Cutting trials were performed on a near balanced ferrite/pearlite microstructure (AISI 1045 steel) with a range of undeformed chip thicknesses spanning across the tool edge radius. The characteristics of AE r.m.s signals were studied for conditions when the tool was rubbing the workpiece. This base signal signature was used to study and contrast AE signals to other machining parameters. This study enabled the identification of threshold conditions for occurrence of minimum chip thickness. The value of minimum chip thickness predicted by this new approach compares reasonably well with that existing in published literature.