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 con ducted. The AE transducer was characterized by subjecting it to known excit ations both directly and through a plastically-deforming material. The AE a ctivity in well-controlled tensile tests was characterized using root-mean- square (RMS) AE measurement. A model of RMS AE based on dislocation generat ion, morion and annihilation was formulated. Model parameter values were de termined using tensile-test results. Finite element calculations of the str ain distributions in the cup-drawing process using experimentally determine d friction boundary conditions were performed. The calculated strain and st rain rate were used in the RMS AE model to predict AE activity in cup-drawi ng. The RMS of AE signals was measured in cup-drawing, and predicted and me asured results were compared. Transducer and signal transmission path characteristics have significant ef fects on measured AE signals. If only correlations between process variable s 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 re sults was capable of predicting RMS AE measurements in cup-drawing. The lar ge 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. (C) 2000 Elsevier Science S.A. All rights reserved.