Advanced simulation of nitrogen cooling in extrusion of light alloys

Extrusion of light alloys is considered one of the most relevant processes in high-volume manufacturing. Production rate shall be kept as high as possible; however, the process bears limitations due to the operating conditions and mechanisms, which yield a large amount of heat generated by deformation energy and friction forces. Profile temperature likely reaches values close to 580 – 590 °C and the resulting thermal stress may reduce the tool life and lead to cracks and defects in the profile. Therefore, cooling of the zones where the higher temperatures occur is instrumental. Nitrogen has been recently brought at the forefront as a coolant, thanks to its low boiling point at atmospheric pressure. However, the design of cooling channels mostly relies on models that include either the liquid or the gas phase. The present work is focused on assessing the homogenous-flow approach as a method representative of the involved physics, also not being as computationally demanding as those simulating both phases. A Finite Element model was developed in a multiphysics environment, encompassing both the extrusion process and the nitrogen flow. The latter consisted of a homogeneous flow requiring dedicated formulation of thermophysical properties. Transient analyses were carried out with different models and the results were validated against an experimental dataset that stemmed from AA6063 billets extruded at variable speed in a reduced-scale industrial line. The ability to predict temperature measured at a location close to the billet was evaluated. The results from homogeneous flow modeling appear the most accurate, whereas modeling only the liquid phase leads to an overestimation of the cooling effect, as opposed to the underestimation associated with including the sole gas phase. Running time also proved as short as industry typically requires.