Phase Field Method for the Assessment of the New-Old Billet Material Interaction during Continuous Extrusion Using COMSOL Multiphysics

During the hot extrusion process of metals, billets are continuously loaded into the press and joined together under high hydrostatic pressure, forming a single extruded profile. Contamination at the billet-to-billet interface, such as oxides and dust residues, produces a welded zone (i.e. charge welds) with compromised mechanical properties, leading to the scrap of the resulting profile portion. To optimize the discharging process, the exact starting point and the extent of the billet-to-billet interaction must be precisely identified. This study aims to develop an innovative model based on phase field method to capture the interaction between immiscible fluids at high viscosity, capable of predicting the charge welds evolution within the COMSOL Multiphysics FEM code. To validate the model, two industrial case studies were experimentally investigated, involving the extrusion of AA6060 and AA6082 profiles with different process parameters and cooling conditions. The collected data were compared with simulation outcomes, revealing a good agreement with errors always below the 8% both in terms of charge welds onset and extent. This validation proved the reliability of the proposed model in accurately predicting extrusion defects.