Numerical simulations for studying the influence of friction in forging

The modelling and simulation of forging has reached a matured stage, but the friction and friction models got only scant attention; this work intends to fill up that gap. Here, arbitrary Lagrangian-Eulerian (ALE) finite element method (FEM)-based numerical simulations are carried out for the forging of aluminium workpiece by considering two friction models - Coulomb-Siebel and Tresca. A relation between Coulomb's coefficient of friction and friction factor has been established based on the slab method. The forging load is obtained by calculating the reaction force on the die as well as from energy method. Energy method provides more accurate and consistent results. Forging load and bulge increase with the friction, but at high friction, the effect is minimal. Bulge is found to be more sensitive to friction than the forging load. The distribution of normal stress is quite different on the die-workpiece interface compared to that on a parallel plane in the interior. The phenomenon of fold-over observed at high friction and high reduction observed in a Lagrangian formulation is absent in ALE formulation. The fold-over phenomenon occurs due to mesh distortion. It is not observed in a workpiece with round corners, even while using Lagrangian formulation.