This paper presents the authors' review of their recent activity in the development of a general purpose finite element program for the analysis of forming processes. Such activity emphasizes our efforts to produce a comprehensive package of finite element related technology, which makes the analysis of practical problems feasible.
In order to simulate a non-steady state industrial forming problem a considerable amount of increments is usually necessary. Therefore, it is economically important to make the increments as large as possible without losing accuracy or overly increasing the number of iterations needed for convergence. Up-to-date techniques incorporated in an updated Lagrangian formulation help achieve this. In particular, the use of a strain measure derived at the mid-increment and the use of projection techniques in the integration of the constitutive equations prove useful.
Most industrial forming problems are driven by non-linear boundary conditions that result in dramatic changes in contact surfaces during the course of an analysis. Efficient algorithms have been obtained that impose the contact constraints either by means of Lagrangian multipliers (gap elements), or by direct application of boundary displacements. Within the latter framework, two dimensional geometrical die profile descriptions are automatically translated into boundary conditions at the nodes that come in contact with the dies. Also, any possible rigid body die motion, variable in time or not, can be accommodated.
One of the most elusive problems in forming processes is friction. The authors have used both a constant shear stress and a Coulomb friction model; however, these models may be overly simplistic if the coefficients are not allowed to vary with process parameters and local conditions.
Large amounts of non-uniform deformation usually produce finite element meshes so distorted that the results become unreliable. Rezoning has been the answer to this problem. As yet, the goal of fully automatic rezoning has not been achieved. However, measures of mesh quality have been implemented to assist the user on when to rezone.
Another important consideration in the analysis of forming processes is material behaviour. Although rate-independent perfect von Mises plasticity is accepted as adequate in some instances, it is necessary to include work hardening, temperature effects and strain-rate effects on the flow stress for a more sophisticated approach.
An example meaningful in the context of metal forming analysis is presented as illustration of the capabilities dealt with.