The study is concerned with the analysis of unconstrained axisymmetric piercing as a nonsteady forging process by the rigid-plastic finite element method. The rigid-plastic finite element formulation is one of the most efficient numerical tools to obtain detailed informations including the distribution of stresses and strains in the analysis of metal forming processes.
In the analysis of axisymmetric piercing, the initial velocity field is generated by assuming the material as a linear viscous material to begin with in order to facilitate the input handling and to ensure better convergency. The strain-rate hardening effect for nonsteady deformation and the friction of the die-material interface are considered in the formulation. An effective method for rigid body treatment is also incorporated in the developed program. The effect of aspect ratio of the specimen with different frictional conditions is discussed.
The experiments are carried out for aluminum alloy specimens (A12024) with different specimen heights. It is shown that the experimental results are in excellent agreement with the finite element simulations in deformed configuration.
For load prediction the theoretical prediction shows excellent agreement with the experimental load in the initial stage of loading before fracture of the specimen is not initiated. However, after the fracture the difference between the simulation and the experiment in load becomes wider as deformation proceeds. Distribution of stresses, strains and strain rates has been found for the cases in computation. On this basis several fracture criteria are introduced in order to check the fracture initiation. It is found that maximum shear criterion is capable of good fracture prediction. The developed program can thus be effectively used for prediction of forging load, deformed shape and workability in axisymmetric forging problems.
