Transient Thermal Analysis of Multiple Extrusion Runs with Nitrogen Cooling by Means of Qform Code

In hot extrusion of light alloys, nitrogen cooling has become a strategic solution to mitigate thermal issues from high deformation rates and frictional heating, improving surface quality, extrusion speed, and die life. However, current cooling system designs remain largely empirical, and the limited use of predictive modeling and experimental monitoring often leads to inconsistent evaluations. This work proposes a dual-step procedure for transient numerical analysis of multiple billets with nitrogen cooling. First, a 1D numerical model of nitrogen cooling is simulated in a simplified environment reproducing extrusion thermal conditions, requiring negligible computational time. The resulting heat transfer coefficient (HTC) and nitrogen temperature are then integrated into the process model, implemented in Qform code, as additional boundary conditions. This approach enables the fully 3D extrusion model to account for nitrogen cooling effects not only on thermal gradients but also on aluminium flow and die resistance. A porthole die with three tube-shaped openings for hollow profile extrusion was experimentally tested under cooled and uncooled conditions, with thermal behaviour monitored by eleven thermocouples within the tooling set. Experimental–numerical comparison confirmed the advantages of numerical simulation for cooling channel design and the limitations of experience-based approaches.