Sytnyk S. INCREASING PRODUCTIVITY AND REDUCING METAL CONSUMPTION WHEN STAMPING BLANKS FOR MEDIUM-CALIBER SHELLS FROM LOW-CARBON STEEL

Dissertation for the degree of Doctor of Philosophy in the field of knowledge 13 – Mechanical Engineering in the specialty 131 “Applied Mechanics” - National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” MES of Ukraine, Kyiv, 2025. The dissertation is devoted to the study of methods for increasing the productivity of processes of plastic forming of steel of axisymmetric products with variable wall thickness, using the method of hot drawing with thinning, to reduce the number of transitions of drawing with thinning during their manufacture, as well as the study of methods for reducing metal consumption in the manufacture of these products. An analysis of literary sources on existing technologies of plastic forming of products with variable wall thickness was conducted. The technologies include operations of hot deposition and subsequent reverse extrusion with the distribution of hollow semi-finished products, drawing with thinning and the final crimping operation. For the first time, using the finite element method, a computational analysis of the transitions of hot deposition and subsequent reverse extrusion of round hollow semi-finished products from a square-section billet made of low-carbon steel was carried out. To design the working tool, the distribution of normal stresses on the contacting surfaces of the semi-finished product with the deforming tool was analyzed. The heating temperature of the deforming tool and the deformation rate were established, which ensure plastic shaping under hot deformation conditions. The initial heating temperature of the billets and the temperature distribution in them at the end of the deformation process were determined. The energy-force modes of deformation and the forces for removing deformed billets from dies were determined, the distributions of specific forces on punches, dies and ejectors were determined. The final shapes and dimensions of the semi-finished products with the distributions of stresses and strains were established. It was found that the reverse extrusion of square-section blanks without prior deposition of corner zones leads to the formation of protrusions on the upper end of the hollow product, which negatively affects subsequent drawing operations with thinning, and the introduction of an additional operation of facing the protrusions will lead to significant metal waste, which is unacceptable in mass production. Using the analysis of the distribution of deformation intensity, the nature of the development of the structure of the material of the bottom part of semi-finished products after hot reverse extrusion of round and square-section blanks was compared. The use of a square blank provides a more intensive development of the metal structure by plastic deformation in the bottom parts and walls of the products. Using the finite element method, a computational analysis of further transitions of stamping semi-finished products after the reverse extrusion operation, namely hot and cold drawing with thinning, was carried out to obtain semi-finished products of the desired shape for performing the final crimping transition with the necessary development of the metal structure by plastic deformation and achieving the specified mechanical properties along the height of the sleeve wall and pallet. The dependences of the drawing forces on the displacements of the punches, the shapes and dimensions of the semi-finished products after drawing, and the distribution of the intensity of deformations were established to assess the development of the metal structure by plastic deformation. The need for a transition to align the bottom part of the sleeve semi-finished product after the hot drawing with thinning operation through two consecutively arranged matrices was determined, since as a result of deformation, the bottom is curved outward, which does not allow installing the obtained semi-finished product in the working zone of the matrix for performing the cold drawing with thinning operation. For the first time, finite element modeling of the processes of the final crimping transition with simultaneous deposition of flanges on the bottom part of the sleeve blanks was carried out, taking into account the accumulated deformations in the semi-finished products after drawing with thinning. The deformation forces, deformation intensity distributions and final shapes and sizes of the sleeve blank were established. It was proved that from the protrusion on the bottom part, which was formed during the hot reverse extrusion transition, it is possible to obtain a flange of the required shape and size. For the studied transitions of the pallet forming, the designs of dies were developed and designed, which ensure the obtaining of the required shapes and sizes of the semi-finished products.