Physical and numerical analysis of the metal flow over the punch head in backward cup extrusion of aluminium

Material flow of aluminium-alloy slug over the punch head was studied in backward cup extrusion process by physical modeling technique combined with FE-simulations. Specially designed intrinsic tube/circle pattern made of contrast material was used for the purpose. Combination of conversion coating and soap film was used as lubricant in the process. Due importance was given to extension of end-face of slug over the punch head. New physical pattern technique was very useful as it allows calculation of the extension of surface all over the inner wall of the cup with ease. Degree of surface extension over the punch head was observed to vary along the cup length. Close to the base of the cup, extension was very high compared with extension at top of the cup. Use of new physical pattern technique in qualitative friction prediction was discussed. Moreover, the expansion of the slug surface over the punch head was well reproduced by a DEFORM™ FE-model when friction was modeled according to specific guidelines.