Modeling of aluminum alloy profile extrusion process using finite volume method

摘要

The most popular numerical method used for simulating aluminum alloy extrusion process is finite element method (FEM). But aluminum alloy profile extrusion process is a metal forming process with severe and large plastic deformation. If finite element method is used to simulate aluminum profile extrusion process, mesh always distorts quickly and frequent remeshing is needed. In addition, the checks for node-separation-from or node-contact-to die surfaces are also frequently needed. The continuous remeshing and node-separation-contact checks usually decrease the accuracy of FEM-based simulation results and increase the CPU time. In this paper, finite volume method (FVM) based on Euler mesh is used to simulate three-dimensional steady or transient aluminum alloy profile hot extrusion process. Semi-implicit method for pressure-linked equations (SIMPLE) algorithm is used to calculate the velocity field and the pressure field of the extrusion process. The dynamic viscosity coefficient of the material mostly dependent on temperature and the effective strain-rate is updated in every SIMPLE inner iteration. At every exterior time step, the method of volume of fluid (VOF) is applied to catch the transient free surface of the material. "Moving grids system" is also used to deal with the moving problem of the boundaries of the calculated domain caused by the moving of the extrusion ram. To ensure the stability and efficiency of the simulation, automatic adjustment of the time increment is realized. Two typical extrusion processes are simulated by the FVM model of this paper. Some results are compared with those simulated by FEM. The material flow characteristics from transient state of extrusion process to steady state of extrusion process are also discussed.