Finite element modelling of the charge welds evolution in a porthole die

Although the extrusion process is regarded as a continuous process, in practice billets are
discretely loaded into the press. The joining of two consecutive billets is guaranteed by the high
hydrostatic pressure of the process. Nevertheless, mechanical proprieties of the profile in the
welded region are lower than those of the adjacent area thus leading to the discarding of the welded
segment. Extension of the segment is mainly affected by the interaction of seam and charge welding
phenomena and, nowadays, its prediction is still a tricky task involving rough empirical relations or
labour intensive analyses. Aim of this work was to identify the starting and exhausting points of the
charge welds evolution inside an industrial multi-profiles die, in order to determine the exact
position and the minimal length to be scraped. The extrusion of four AA6060 hollow profiles
through a multi-hole die were preliminary monitored in an industrial press by accurate recording of
the process loads, temperatures and speeds during the process. The four profiles were sectioned
starting from the ‘stop mark’ then grinded and etched in order to investigate the location and the
dimension of the zone to be ridded. While the experimental activity is detailed elsewhere, this paper
is focused on the finite element modelling of the process. The numerical simulation was performed
by means of the Altair HyperXtrude code and predictions compared to experimental data with a
particular focus on the computation of the charge evolution. It was found a good agreement both in
terms of general trend and prediction of the exhausting points so thus proving the code to be a
reliable tool for an accurate determination of the scraps.