Ural Federal University Named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia:

Yu. N. Loginov, Professor, Department of Metal Forming, Doctor of Technical Sciences, e-mail: j.n.loginov@urfu.ru

M.N. Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, Yekaterinburg, Russia:
Yu. V. Zamaraeva, Acting junior scientific researcher of laboratory of strength problems, e-mail: zamaraevajulia@yandex.ru
B. I. Kamenetskiy, Lead Researcher at the Laboratory of Strength, Candidate of Technical Sciences, e-mail: kamenetski@imp.uran.ru

The aim of the work is to assess the influence of the reaction from the shell on the stress state during the upsetting of the cast magnesium billet. The work consists of experimental and analytical parts. The experimental part shows the results of an experiment on the upsetting of a cylindrical billet of magnesium grade MG90 using a vertical press of grade DB 2240 with a nominal force of 10 MN in two versions: with and without a shell. The assembly configuration assumed the presence of a shell whose height exceeded the height of the workpiece. Punches were inserted into the formed cavities. When the pressure was applied to the punches, the height of the cylindrical workpiece decreased, and the diameter increased. As a result, the diameter of the shell also increased and a reaction was created to change the shape of the workpiece. Compression stresses occurred between the workpiece and the sheath, which made it possible to achieve a relative strain of 24%. No traces of destruction were found. For comparison, a cylindrical billet of the same magnesium was deposited without backwater on the same press. Already at a relative strain of 6%, cracks appeared both at the ends and on the side surface of the workpieces. Thus, experiments have shown that the presence of the shell allows you to increase the logarithmic deformation to failure at least 4.5 times. To assess the stress-strain state, the finite element method implemented in the DEFORM-3D software module was used. The problem statement included a description of the geometry of the deformation zone in the initial state, a description of the physical and plastic properties based on the reference data, and setting boundary conditions in the displacements. The Siebel friction index in the process is 0.2, which corresponds to the use of lubricant, as described in the experimental part of the work. Elastic and plastic properties of materials are set based on the program interface. The use of computer modeling made it possible to obtain a visual representation of the movements of the metal and the distribution of deformation throughout the entire precipitation cycle. Upon transition to the material of the cylindrical billet, an increase in the modulus of the radial stress values is observed up to the level of –330 MPa. Average stresses are shown for the option with and without a shell. In the case of using the shell, zones with high modulus average stress levels up to — 390 MPa were identified. To solve the problem without a shell, it was necessary to apply a different stress scale, since they are shifted to the region of values lower in absolute value. In the case of settlement without a shell, the maximum absolute value of the average stress is –190 MPa, which is two times lower than the previous version. The highest level of deformation is achieved in areas adjacent to the edges of the workpiece to the punches. The degree of deformation in the volume of the workpiece can reach a value of 0.6. It is noted that the concentration zones of increased strains coincide with the zones of increased average stress modulo, which reduces the likelihood of fracture. The performed experiments and the performed calculations confirmed the possibility of cold-formed cast magnesium deformation. This eliminates the operation of heating the metal before the pressure treatment operations, which creates the possibility of achieving the effect of strain hardening and avoiding the risk of fracture.
This research was partially funded under Decree No. 211 of the Government of the Russian Federation, Contract No. 02.A03.21.0006, as part of the Governmental Assignment No. АААА-А18-118020190104-3 (“Pressure”), as well as under the Project No. 18-10-2-24 of the Programme adopted by the Ural Branch of the Russian Academy of Sciences.

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