EVOLUTION OF THE STRESS–STRAIN STATE OF POROUS BILLETS  IN HOT FORGING BY EXTRUSION OF AXISYMMETRIC WORKPIECES WITH AN AXIAL HOLE

Abstract

The evolution of stress-strain state and the distribution of temperature and relative density within the volume of a porous billet when hot forged by extrusion to produce axisymmetric workpieces with an axial hole was studied by computer simulation. The hot forging process was modeled using the finite element method and the DEFORM 2D/3D software package. Analysis of the simulation results showed that, in the initial stages of the process, the region of strains, stresses, and relative density of the material developed under the conical protrusions of the deforming punches, and these parameters decreased radially from the center of the forged workpiece to its periphery. As the axial strain increased with further deformation, the region of elevated stresses and density extended deeper into the material, spreading from the center of the forged workpiece to its periphery. In the final stage, after the matrix cavity was filled with the forged material, the relative density and stress intensity averaged over the workpiece, while the strain intensity noticeably decreased in the radial direction from the center to the periphery after complete compaction. This was explained by the deformation that occurred in the final stage when the forged material filled the pore volume in the consolidation process after the working capacity was filled. The forging force increased sharply when the matrix cavity was filled completely and the material was compacted but increased monotonically in the initial stages of the process.