OBRABOTKAMETALLOV Vol. 24 No. 2 2022 TECHNOLOGY This part of the solution is given to evaluate the difference in the metal properties in the cross section when using an extrusion scheme with low elongation ratio. Fig. 4 shows the solution of the problem in the form of equal-level areas for the transition process from the initial non-stationary stage to the stationary stage. If the strain remained constant along the rod length in the stationary stage (Fig. 3), then this condition is not fulfi lled for the rod front part. The minimal strain is localized in the rod front end center. The maximum strain is localized closer to the periphery, but it barely reaches the value of 0.7. It should be noted that the strain determined through the cross-sectional areas was 1.62, which is 2.3 times higher than the previously mentioned value. The graphs are plotted in Fig. 5 to evaluate the resulting inhomogeneity. Relative radial coordinate r/R is introduced, where r is the current rod radius; R is the rod external area radius equal to half of rod diameter. The course of the curves on the graph shows that as the distance from the end increases, the values of the strain degree increase from zero to the level of the stationary stage of extrusion. The curves for the rod central part are most densely located, which indicates the minimal gradient in this zone. The lines are located more rarely closer to the periphery. This corresponds to the graph aggregation manner on Fig. 3, b, which was obtained for the stationary stage, however, with signifi cantly different nominal parameter values. The graph analysis in Fig. 5 also shows that the rod central layers obtain a strain constant level earlier than the peripheral layers. The stationary process is achieved with less metal motion. The resulting strain distribution extends to the initial and boundary problem conditions. There is a wide variety of parameter ratios in production. Machine time cost was about two weeks without considering the time for debugging the system for several months. Therefore, sorting through all possible variants of production technologies and processing techniques is a rather expensive procedure. In this case, recommendations were developed for the considered option, but an attempt has been made to extend it to a class of technologies related to the extrusion with light reduction. The consideration of the strain fi elds helps to determine the accumulated value of the hardening characteristic. But it is not clear here, why this effect is achieved. Therefore, Fig. 6 shows the stain rate fi eld (s–1). Since the degree of deformation is an integral of the strain rate along the trajectory of the elementary particle, there are two ways to form a fi eld of increased strain rates – either due to high strain rates, or due to the long-term use of moderate strain rates. The fi gure shows that an extremely high strain rates zone W is formed near the parallel land front part of extrusion die. At this point there is a sharp change in the metal motion direction and the strain tensor shear component increases signifi cantly. It can be concluded that there is a minimum strain that is needed to study the metal structure. The reduction rate calculated by the equation (2) is 80 % as shown previously. If only 40 % reduction rate is suffi cient to achieve the properties and obtain the desired structure, then, in accordance with equation (3), the degree of deformation is 0.51.As can be seen from the graph in Fig. 5, this value is already achieved at a distance of Fig. 4. Distribution of the strain degree in the longitudinal section in the nonstationary initial stage Fig. 5. Graph of the distribution of the strain degree in the cross sections of the rod depending on the distance from the front end at various relative radial coordinates r/R
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