Wear and frictional behaviour of high strength steel in stamping monitored by acoustic emission technique

Friction surfaces can be monitored by acoustic emission (AE) technique and the AE-signal depends on the conditions prevailing between the friction surfaces. AE from a forming operation contains measurable data from events such as galling, tool wear, lubricant penetration, stick–slip, wrinkling, necking in the sheet material and cracking in the tool or the sheet material. The detected AE is directly proportional to the energy (mechanical) consumed between the contacting surfaces and can therefore be used to estimate the forces acting on these surfaces. A change in the tribological parameters, such as materials in contact, the efficiency of lubricants, the roughness of the contacting surfaces, relative velocity between the contacting materials and contact pressure can be monitored by AE technique. Wear tests have been made using flat dies and a U-bending tool. The results indicate that the U-bending tool can be used to study wear behaviour and it simulates forming over the linear portion of a stamping tool. AE, punch force and tool temperature are shown to be essential in the evaluation and understanding of the wear process. The result shows that the surface treatment and surface quality of the tool are important for the wear behaviour. These results indicate that it is possible to use uncoated hardened tools provided that a minimum tool surface quality is maintained. These results also show that hot-dip galvanised high strength steel (HSS) wears the tool out less than uncoated HSS.