Acoustic emission monitoring of sheet metal forming: characterization of the transducer, the work material and the process

A systematic investigation of acoustic emission (AE) in cup-drawing was conducted. The AE transducer was characterized by subjecting it to known excitations both directly and through a plastically-deforming material. The AE activity in well-controlled tensile tests was characterized using root-mean-square (RMS) AE measurement. A model of RMS AE based on dislocation generation, motion and annihilation was formulated. Model parameter values were determined using tensile-test results. Finite element calculations of the strain distributions in the cup-drawing process using experimentally determined friction boundary conditions were performed. The calculated strain and strain rate were used in the RMS AE model to predict AE activity in cup-drawing. The RMS of AE signals was measured in cup-drawing, and predicted and measured results were compared. Transducer and signal transmission path characteristics have significant effects on measured AE signals. If only correlations between process variables and RMS AE is sought, the combined transducer, signal path and AE effects can be used. The RMS AE model developed using experimental tensile-test results was capable of predicting RMS AE measurements in cup-drawing. The large AE activity in the initial stages of plastic deformation in cup-drawing makes AE measurements easy and meaningful, but the small signal after this part of the process makes the monitoring of subtle changes in this part of the process doubtful.