Investigating galling wear behaviour in sheet metal stamping using acoustic emissions

Galling wear in sheet metal stamping processes can degrade the product quality and adversely affect the mass production. Studies have shown that acoustic emissions sensors can be used to measure galling. However, the link between the features of the acoustic emissions signal and galling during complex manufacturing processes, such as sheet metal stamping, are not well understood. In the first section of this paper, it is shown that time domain features of the acoustic emission signal, such as RMS and peak, can be used to identify when the tooling is unworn or severely worn. These results were correlated with the wear measurement of the maximum depth of the surface profile of the stamped part. In the second section of the paper, time-frequency techniques were used to understand the characteristics of the AE signal associated with wear of the sheet metal stamping dies. The results show that it is possible to identify changes in acoustic emission signal using time-frequency techniques much prior to the observation of major changes in the time domain features and visual observation of wear on parts. In the third section of the paper, a new acoustic emission feature known as mean frequency estimate is proposed for the condition monitoring of the stamping wear. This mean frequency estimate feature showed a clear shift in the acoustic emission signal much before the observation of severe wear. The methodology used in this paper to study wear progression can lay the basis for real-time monitoring of tool wear in the stamping industry.