Monitoring of friction processes by the means of acoustic emission measurements—deep drawing of sheet metal

Abstract

Acoustic emission generated in deep drawing processes gives information about the friction and the forming processes between tool and workpiece. This information can be used to supervise or improve the forming process. Measurements of acoustic emission in manufacturing machines in production lines shows that different events such as, galling, tool wear, lubricating failure, different viscosity of lubricants, stick-slip, necking and cracking of the sheet metal can be separated in time- and frequency domain. Laboratory tests show that proportionality exists between the effective output of the friction surfaces and the measured effective output of the AE-sensor in drawing a sheet metal between flat dies. The measured acoustic emission has been influenced by the smoothness, lubricants, relative speeds between the friction surfaces, the contact pressure between the surfaces, galling, changed geometry's of friction surfaces and different types of material in contact. In a forming process will different lubricants result in different lubricity and the measured effective output of the AE-sensor result in a ranking method. The proportionality between the effective output of the friction surfaces and the measured effective output of the AE-sensor established in the laboratory tests has been applied in measurements of acoustic emission in manufacturing machines in production lines. By monitoring the acoustic emission in manufacturing machines, we are able to detect different events, i.e. galling, cracks, toolwear.