Experimental and numerical study of the ironing of stainless steel cups
Résumé
An experimental study of the ironing of austenitic stainless steel cups has been undertaken to (i) quantify the discrepancy (due to tool deformation) between nominal die-punch gap and real final wall thickness; and (ii) to determine the maximum reduction for safe operation of the process. An analytical model has been derived in which the stresses based on the slab method, known to be very efficient for thin products, are augmented for shearing energy at the entry and exit of the deformation zone. A friction-factor model has been chosen to represent friction due to the rather large normal stresses involved, and work-hardening has been included in a very simple yet efficient way. The comparison of predicted forces with experimental forces is quite satisfactory. Moreover, finite-element modelling has been used to check the analytical model giving excellent agreement, proving that the remaining discrepancies between theory and experiment are mainly due to the friction factor and/or constitutive behaviour used. From the FEM results, the states of stress in the cup wall during and after drawing are analyzed and support the hypotheses of the analytical model. The maximum reduction is discussed in terms of necking and fracture criteria (the Swift and the Hill criteria) and compared with experimental findings.