Simulation of steady-state extrusion through a hollow die using HyperXtrude FE software

The design of dies for the light-metal extrusion process is based primarily on the experience of the die designer. The performance of the die is only known after the die is manufactured and tested on the extrusion press. It is still a major challenge for the die designer to get the die the first time right without the need of correction. To achieve this, the die designer needs a powerful tool that can provide an insight into the metal flow through the die at the design stage. Computer simulation based on the finite element (FE) method can be such a tool, if the software, material model, material data, boundary conditions and simulation parameters are all appropriate to represent the light-metal extrusion process in reality. Many of the commercial FE codes are based on the updated Lagrangian approach and using them to deal with the industrial extrusion problems with large billet and tooling sizes is quite time-consuming. HyperXtrude is an FE code based on the Arbitrary Lagrangian-Eulerian (ALE) approach and needs far less time to simulate the process in the steady state. The present study was aimed at assessing the capabilities of HyperXtrude (version 7.0) to simulate the extrusion process (i) in its simplest form, through a solid die to produce a bar, and (ii) in a complex form, through a porthole die to produce a rectangular tube. The results showed that simulation was indeed highly efficient in the case of extruding a round bar. After 25 iterations, the process entered the steady state within 0.5 h with a Windows XP PC. Interesting features of the extrudate could be captured, including the exit velocity distribution, temperature distribution and die deflection. In addition, it was found that when the friction coefficient in the Coulomb friction model was larger than 0.2, its effect on extrusion pressure and exit temperature became negligible as the critical friction stress was larger than the shear yield strength of the billet material at the extrusion temperature. In the case of simulating extrusion through a porthole die for a rectangular tube, simulation revealed many features in the steady state, when the billet material flew out of the die bearing, including the velocity distribution, strain rate distribution and temperature distribution. Of more interest was the observation of the displacement of the mandrel of the die, as a result of the deformation of the die core under high compressive stresses. The effects of boundary conditions such as heat transfer type and local heat transfer parameters on temperature distributions across the billet and extrusion tooling were analyzed.