Advanced multi-physics models for the optimization of the hot extrusion process of light alloys
During the hot extrusion process, a cylindrical pre-heated billet is inserted into a container and is forced by a hydraulic press to flow through a shaped die in order to obtain, as final product, a profile with a constant cross-section (Fig.1). Aluminum extrudates have become prominent in several industrial fields such as furniture design, railway transportation and construction due to their high flexibility in shape complexity, high strength-to-density ratio and corrosion resistance. In response to the growing demand for high-quality, complex profiles, numerical simulation offers a competitive solution for process optimization, scrap reduction and productivity enhancement. In this context, this work aims to present an innovative numerical model developed within COMSOL Multiphysics® for simulating the extrusion process. In detail, the 3D model of the extrusion process is simulated by coupling different modules depending on specific objectives [1]: the metal flow under deformation is treated as a non-Newtonian fluid with very high viscosity (Laminar Flow Module), which simultaneously exchanges heat with the tooling set (Heat Transfer with Solid and Fluid Module) and the cooling channels (Non-Isothermal Pipe Flow Module). The cooling system (Fig.2), using liquid nitrogen as a coolant (Homogenous Fluid Model approach to account for the nitrogen phase-change), contributes to reduce temperatures in critical zones. The fully coupled model, as presented, allows the prediction of the thermal field (Fig.2), the extrusion load, and the velocity field of the material flow during the whole extrusion process. If required, the Phase Field model can be integrated to evaluate the evolution of the transition zone between two subsequent extruded billets, which is an unavoidable scrap to be reduced during multi-billets extrusion. The Topological Optimization Module (Fig.3) [2] can be used to design the cooling channel, where the die is treated as a porous volume “virtually milled” by the nitrogen flow (Darcy flow model) in order to fulfil specific objective functions such as homogenous cooling, minimization of the nitrogen consumption. In addition, it is demonstrated that COMSOL with MATLAB can be integrated with an external optimizer to automatically design the tooling set by using genetic algorithms (Fig.4) [3]. Several industrial case studies were presented and discussed to demonstrate the potential of the numerical models developed within COMSOL Multiphysics® for the hot extrusion process of light alloys.
