Numerical modelling of large deformation in metal powder forming

In this paper, the transient dynamic analysis of metal powder during the cold compaction process is simulated by the finite element method based on a ‘Total’ and ‘Updated’ Lagrangian formulation. Since the compaction process involves a very large reduction in volume, the behaviour of the powders is assumed to be that of a rate-independent elasto-plastic material. The process is therefore described by a large displacement finite element formulation for the spatial discretization. A generalized Newmark scheme is used for the time domain discretization and then the final nonlinear equations are solved by a Newton-Raphson procedure. A combination of a Mohr-Coulomb and elliptical cap yield model is utilised as a constitutive model to describe the nonlinear behaviour of powder materials. An incremental elasto-plastic material model is used to simulate the compaction process and a plasticity theory for friction is employed in the treatment of the powder-tooling interface. The interfacial behaviour between the die and powder is modelled by using an ‘interface’ element mesh. Finally, the powder behaviour during the compaction of a plane bush, a cutting tool and a rotational flanged component is analysed numerically. The predictive compaction forces at different displacements, the variation with time of the displacement, relative density and stress contours are obtained. It is shown that the proposed large displacement elasto-plastic finite element approach is capable of simulating the metal powder during compaction.