Understanding galling wear initiation and progression using force and acoustic emissions sensors

In the stamping process, tools are prone to an adhesive wear mode called galling. This galling wear mode on the stamping tool results in an abrasive wear modes like ploughing and cutting on the workpiece. To study the adhesive and abrasive wear modes relevant in sheet metal stamping processes, scratch tests were performed under controlled conditions where galling, ploughing and cutting can be observed. Two sets of scratch tests were performed to study the galling behaviour using force and acoustic emission sensors. In the first test set, scratch tests were performed at a different depth of penetration to segregate the non-galling and galling conditions. In the second test set, scratch tests were performed at a different sliding distances to understand the influence of galling on the abrasive wear modes. To study the galling behaviour, acoustic emission and force features from both of the test sets were correlated with profilometry wear measurement features like profile depth, wear index, attack angle and volume measurement of galling. From the quantitative measurement of galling on the indenter, a minimal lump was observed on the indenter when the cutting at the edges of scratch was observed. A much larger lump was observed on the indenter for conditions when fracture was observed on the workpiece at the centre of the scratch. The acoustic emission burst signal and unstable force behaviour was mainly observed when the signficant lump was observed on the indenter. The methodology adopted to investigate galling wear in this study lays the strong foundation to develop real-time monitoring systems to observe the transition from non-galling to galling conditions.