On the Friction Conditions in FEM Simulations of Cold Extrusion

Friction is a very important issue for calculating the punch force and energy consumption in cold extrusion. FEM simulations are commonly used to investigate this process, but the choice of the friction's model and set-up parameter have influence on the results. In this work FEM simulations of cold forward extrusion of rods were performed using the commercial code DEFORM (TM) in axisymmetric 2D deformation mode with Lagrangian formulation considering Tresca's friction model and two parameters as set-up: constant friction factor m or constant frictional shear stress tau. Over the deformation stages of the process, the influence of the friction parameters on the simulated force-displacement curves was analyzed. In addition, metal flow prediction and the profile of the actual frictional stress at the billet-container interface were studied. For the investigated tooling geometry and dimensions, it was found that for low levels of friction (m <= 0.1), both parameters can be suitably used to study the forming process, since they provided similar force-displacement curves and metal flow prediction. For higher levels of friction, the use of tau as input provided most stable and reliable results, since in this case, the simulated force-displacement curves agreed very well with experimental result, the effective frictional stresses values were more constant, and the relative frictional stresses resulted closest to the input value. (C) 2020 The Authors. Published by Elsevier Ltd.