In-situ Wear Monitoring: An Experimental Investigation of Acoustic Emission During Thread Forming

Abstract

To meet todays economic requirements, continuous supervision of machining processes becomes increasingly important. In this context, estimation of tool wear is considered a difficult task due to complex interactions between tool and workpiece as well as noise originating from the environment. Besides different process parameters such as torque, thrust, or temperature, Acoustic Emission (AE) has emerged as a promising technique for indirect assessment of tool wear in different machining operations such as drilling or turning. Here, AE source mechanisms can be related to plastic deformation, chipping, or elastic interaction of surfaces. Thread forming is a transformative manufacturing process for generating threads in ductile materials. As the thread geometry is manufactured by cold forming of the material, lubricating properties of the Metalworking Fluid (MWF) strongly effect tool wear and workpiece quality. In this work, AE measurements are conducted in context of thread forming. A tribometer is used to carry out thread forming trials under well-controlled experimental conditions. Different MWFs are considered, including lubricating oils as well as water-based MWFs. Time-frequency domain analysis of the AE signal is applied using continuous wavelet transform. Here, different process phases, forward and reverse, can be distinguished according to peak frequencies of the AE signal. Furthermore, using k-means clustering it can be shown that AE energy in different frequency bands can be used as a feature to distinguish different MWF qualities. According to the results, lower energy levels of the AE signal using high performance lubricating oils indicate a dependency between wear rates and quality of the MWF. Altogether, AE appears as a promising technique to develop in-depth understanding of wear mechanisms related to friction contact of tool flanks and workpiece.