Abstract
In the sheet metal stamping process, during sliding contact between the tool and sheet, it is expected that severe events such as tool wear or fracture on the sheet generate acoustic emission (AE) burst waveforms. Attempts have been made in the literature to correlate the AE burst waveform with the wear mechanisms. However, there is a need for additional studies to understand the frequency characteristics of the AE burst waveform due to the severity and progression of the galling wear. This paper will determine the AE frequency characteristics that can be used to monitor galling wear, independent of the experimental process examined. The AE burst waveforms generated during the stamping and scratch tests are analysed in this paper to understand the change in the AE frequency characteristics with the galling severity. These AE burst waveforms were investigated using the Hilbert Huang Transform (HHT) time-frequency technique, band power, and mean-frequency. Subsequently, these AE frequency features are correlated with the wear behaviour observed via high-resolution profilometer images of the stamped parts and scratch surfaces. Initially, the HHT technique is applied to the AE burst waveform to understand the influence of wear severity in the power distribution over the wide AE frequency range. Later, the AE bandpower feature is used to quantitatively analyse the power in each frequency interval during the unworn and worn tool conditions. Finally, the mean-frequency of AE signal is identified to be able to determine the onset of galling wear. The new knowledge defined in this paper is the AE frequency features and wear measurement feature that can be used to indicate the onset of galling wear, irrespective of the processes examined.
Highlights
The increased use of advanced and ultra-high strength steels in car body panels has led to an increase in stamping force and stress on the stamping tools used in vehicle body manufacturing, leading to untimely failure of stamping tools [1]
The new knowledge defined in this paper is the acoustic emission (AE) frequency features and wear measurement feature that can be used to indicate the onset of galling wear, irrespective of the processes examined
This paper aimed to understand the frequency characteristics of the AE signals and how these changed due to the severity of the galling wear
Summary
The increased use of advanced and ultra-high strength steels in car body panels has led to an increase in stamping force and stress on the stamping tools used in vehicle body manufacturing, leading to untimely failure of stamping tools [1]. Galling wear on the stamping tool results in severe scratching of the sheet surface during the stamping process The creation of these scratches on the stamped part surface can be considered as the action of abrasive wear modes such as ploughing and cutting [3,4,5]. Galling on the tool and the subsequent formation of abrasive wear modes on the sheet surface can arise quickly, due to the rapid development of the galling stages [6]. This necessitates the requirement for condition monitoring techniques that can be used to predict the need for timely maintenance of the stamping tools, prior to the detrimental effects of galling on production output and quality. Conventional wear measurement techniques—such as visual and optical based inspection, weight measurements, and surface profilometry—cannot provide timely and/or quantitative information
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