The evaluation of workpiece deformability for the process of two-stage extrusion of hollow hull

A promising direction in the development of technologies is the search and study of new stamping schemes that improve the quality of parts and expand the possibilities of cold deformation processes. From the point of view of reducing the workload on the tool, the most perspective way to obtain hollow cylindrical parts is combined extrusion. Combined schemes can be attributed to methods that provide a significant expansion of the possibilities of cold forging technologies. The disadvantage of methods for the extrusion of hollow parts is the heterogeneity of mechanical properties, which is especially evident in hollow products with a large bottom thickness. The deformation process is carried out according new method in two steps to reduce the irregularity of strain. In the first step, backward extrusion of the hull wall and forward extrusion are simultaneously performed with the formation of a technological ledge in the bottom part of the hull, and in the second step, the metal is displaced from the ledge back into the bottom part of the hull. However, this raises the question of assessing the deformability of the workpiece. The presence in this process of nonmonotonic sign-alternating deformation significantly complicates the determination of the stress-strain state and the assessment of deformability. The article proposes a calculation algorithm that makes it possible to take into account the influence of nonmonotonic plastic deformation on the value of the used plasticity resource. This algorithm includes determining the kinematic characteristics of deformation using mixed Euler and Lagrangian coordinates, estimating the stress-strain state based on the model of an anisotropically hardening body, and determining the value of the used plasticity resource by applying a criterion that allows to take into account the volumetric stress state and the influence of the third stress tensor invariant on the damage accumulation process. The results of the experimental study and finite element simulation of a two-stage extrusion process are also given, confirming the advantage of the combined process in reducing power parameters and deformation unevenness. The presented calculating approach is used to assess the deformability of the workpiece and the value of the used plasticity resource in the process of combined extrusion and can be useful for analyzing methods of intensive plastic deformation.