Study on acoustic emission in machining hardened steels Part 1: Acoustic emission during saw-tooth chip formation

The generation of acoustic emission (AE) in the machining of hardened steels is investigated. It is shown that, in 'hard machining', the energy of the AE signal may be up to two orders of magnitude greater than in the machining of softer pearlitic steels, depending on work material hardness and cutting parameters. This is a result of the transition from continuous to saw-tooth chip formation and, specifically, the periodic, rapid release of elastic strain energy during catastrophic failure within the primary shear zone. Of the parameters which influence the transition from continuous to saw-tooth chip formation, flank land width may be considered unique. In contrast to work material hardness, cutting speed, undeformed chip thickness and tool rake angle, when the transition in chip morphology is effected by an increase in flank land width, there is not necessarily an increase in AE(RMS). Also, within the continuous chip domain, there is no clear relationship between flank land width, feed and AE(RMS). As such and as is shown, AE(RMS) may increase or decrease with cutting tool wear.