The effect of pressure and temperature variations on the FEM prediction of deformation during extrusion.

Abstract

The extrusion process is complex, involving interaction between the process variables and the material’s high temperature properties and is typically conducted at relatively high temperatures because the lower flow stress of the material permits larger section reductions to be achieved. This lowers the power requirements and processing times. Temperature is, perhaps, the most important parameter in extrusion. The flow stress is reduced if the temperature is increased and deformation is, therefore, easier, but at the same time, the maximum extrusion speed is reduced because localised temperatures must be well below any incipient melting temperature. The present investigation focuses on the evolution of the temperature in the billet from upsetting and until the end of the extrusion cycle is reached. The extrusion pressure and the temperature rise are predicted and the pressure–displacement trace and the events which take place in the deformed material during the extrusion process are also simulated. The simulation is compared with data obtained from an experimental extrusion press. All simulations are performed with the implicit finite element code FORGE2. A comparison with experiments is made to validate the predicted temperatures readings from FORGE2 to ensure that the numerical discretisation provides a true simulation of the process. It was found that the extrusion parameters (friction, heat transfer, etc.) are significantly influenced by the temperature gradients produced in the billet during transfer to the container, and after upsetting in the container. These parameters are thus clearly extremely sensitive input data when attempting to simulate the extrusion process.