OBRABOTKAMETALLOV technology Vol. 25 No. 2 2023 Fig. 10. The dependence of the pressing force 1 p on the movement dl of the punch: a = 45° (1); b = 50° (2); a = 55° (3); a = 60° (4) In this case, the increase in the value of the relative porosity ϑ does not exceed 0.05. There is also considerable heterogeneity in the end region of the blanks. The plot of pressure changes on the working plunger is shown in fig. 10. The analytical calculations are performed following the results of the mathematical model, and the results of the numerical solution are obtained by computer simulation using the finite element method. The figure shows the satisfactory convergence of the solution results. The plot shows the variation of the compacting pressure at the main stages of the process. In the transition from the initial to the final stages of the ECAP process, the compacting pressure takes the maximum value. As the angle a increases, the maximum pressure on the working plunger decreases. During the transition from the initial stage of the ECAP process to the final stage, the pressing pressure takes on a maximum value [34–35]. As the angle a increases, the maximum pressure value on the working plunger decreases. Rational technological parameters of pressing porous blanks should provide the maximum permissible pressures on the deforming tool. From this condition, the optimal value of the angle in each specific ECAP process is determined 2a. Conclusions To optimize technological processes of manufacturing blanks and products from powders and porous materials, a sufficiently reliable and simple for practical use mathematical model of the process of semicontinuous ECAP of a plastically compressible medium is developed. The material properties of porous briquettes made by compacting titanium sponge in a closed mold were taken as a model material of initial blanks for the implementation of the studied process. The main stages of ECAP are considered: the initial stage of the process, in which the porous deformable material experiences compression in a closed mold; the stage characterized by intense plastic deformation localized by changing the mold channel angle; the final stage in which the deformable material is compressed to a nearly compact state and flows out of the mold channel as a solid body. The mathematical model makes it possible to determine the energy-power parameters of the ECAP process. In addition to the analytical solution, a finite-element simulation of the ECAP of porous material for a more detailed prediction of porosity along the blank cross section is given. A satisfactory correspondence of the results of calculating the energy-power parameters of the process is shown. The possibility of describing the processes of both compaction and decompaction of materials at the macro level in a wide range of volume plastic deformation will make it possible to more accurately determine the areas of the deformed porous blank subject to high tensile stresses during ECAP, which are potentially dangerous in terms of surface cracks formation and material fracture. References 1. Zhilyaev A.P., Nurislamova G.V., Kim B.K., Baro M.D., Szpunar J.A., Langdon T.G. Experimental parameters influencing grain refinement and microstructural evolution during high-pressure torsion. Acta Materialia, 2003, vol. 51, iss. 3, pp. 753–765. DOI: 10.1016/S1359-6454(02)00466-4. 2. Saito Y., Utsunomiya H., Tsuji N., Sakai T. Novel ultra-high straining process for bulk materials – development of the accumulative roll-bonding (ARB) process. Acta Materialia, 1999, vol. 47, iss. 2, pp. 579–583. DOI: 10.1016/ S1359-6454(98)00365-6.
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