During the last decade it has become common practice to employ the finite element method (FEM) in the study and optimization of metal forming processes [1]. During a metal forming process the mechanical and thermal fields which develop are closely coupled and introduce geometric (finite deformations), material (large plasticity) and contact associated non-linearty`s [2]. As a result, it is of cardinal importance that FE models are both verified and validated (V&V). Once V&V is properly conducted the FEM can be used to conduct "numerical experiments" which are a substitute to real life expensive and complicated experiments.
In the current study the process of hot extrusion of aluminum was investigated by finite element analysis (FEA) in conjunction with hot extrusion experiments. First, the material plastic flow stress manifolds were determined using FEA of upsetting experiments performed under various strain rates and temperatures. The computational model was verified by convergence tests and validated by comparison to experiments. Second, the material flow stress manifolds from the first stage of the study were incorporated in a finite element model developed to study hot hollow extrusion. The model was used to conduct "numerical experiments" in order to examine the influence of initial billet temperature, die geometry, ram velocity and friction between tools and billet on the coupled thermo-mechanical deformation process.
Metallographic examination of the extruded aluminum tubes was applied in order to correlate between the computed thermal and mechanical fields which develop during the extrusion and changes in local material grain size and texture.
References:
[1] Diter, G.E. , Mechanical Metallurgy, McGraw-Hill 1981
[2] Zienkiewicz, O.C. and Taylor, R.L., The finite element method: Volume 2 Solid and fluid mechanics and Dynamics and Non-linearity, McGraw-Hill 1991
