Dynamically loaded tribo-systems in plastc forming operations, part II --- monitored by acoustic emission

Sammanfattning: The dynamic friction process and contact surface between tool and working material in a plastic forming process is hard to describe in mathematical form and hard to monitor and control in real time. High production speed and highly optimised forming operations result in great demands on the control equipment. Especially if the influence from variations due to the tool, work material and the friction surfaces between working material and tool can not be minimised and are essential for the quality of the product. Friction surfaces can be monitored with acoustic emission (AE) and the AE-signal depends on the lubrication between the friction surfaces. The power of the AE-signal increases with ungreased friction surfaces compared in more effectively lubricated surfaces. Differences in detected acoustic emission between different lubricants can be measured and this information can be used to classify different lubricants and the performance in the investigated forming operation. Acoustic emission from a forming operation contains measurable information from events as galling (welded work material on tool), wear of tool, penetration of lubricant, stick-slip, wrinkling necking of sheet material and cracking in tool-material or working material. The detected acoustic emission is directly proportional to the mechanical power consumption in a friction surface and can therefore be used to estimate the forces on the friction surfaces. A change in the tribological parameters, as material in contact, the efficiency of lubricants, the roughness of the friction surfaces, relative velocity between the friction materials and contact pressure can be monitored with acoustic emission. Mounting and adjusting of tool parts or correction of holding forces in deep drawing operations can be optimised by minimising acoustic emission due to influence of boundary layer friction and wrinkling. Critical friction surfaces can be monitored with consideration to the wear of the friction surfaces. The momentary acoustic emission contains information about the status of wear at the friction surfaces and if the wear is a wear-in or a wear-out process. A further development of the acoustic emission monitoring, primarily regarding methodology, the performance of the measurement equipment and methods of analysing measured data, should lead an increased implementation of the method, measuring and monitoring different forming operations and production lines. This will in the end result in new ways to increased production quality and improved quality check. This work is divided in two volumes, ''Dynamically loaded tribo-systems in plastic forming operations, part I --- actuated by cyclic mechanical stress'' and ''Dynamically loaded tribo-systems in plastic forming operations, part II --- monitored by acoustic emission''. Part I deal with the subjects magnetostrictive actuators, vibration actuated tribosystems and vibration assisted wire drawing. Part II deals with the monitoring of tribosystems using acoustic emission.