OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 Fig. 6. Distribution of the strain rate (s-1) in the longitudinal section of the central bar (YZ plane) when the axes of the die channels are located: along the axis of the rectangular groove (W is a maximum strain rate) (a); along the radius of the container (N is a maximum strain rate) (b) а b The strain rates in both variants increase as the metal approaches the die opening. The metal remaining in the container is a rigid zone. The maximum strain rates (W, N) occur in the zone of the highest shear strain when the direction of the metal changes, and its values are of equal level (50 s-1). Fig. 7 shows the initial moment of the blank deformation by angular pressing and the pressed bars with the strain field when the die channels are arranged along the axis of the rectangular groove (fig. 7, a) and along the radius of the container (fig. 7, b). Here it can be seen that already at the initial stage of the deformation process in both variants there is a non-uniform distribution of the strain degree, with the highest strain degree of the outer bars in the first variant (fig. 7a) on its peripheral part on the side bordering the central bar. In this case, the difference in the strain degree over the diameter of the peripheral bar reaches 28 %, while in the central bar it does not exceed 10 %. In the second variant of the channel axes arrangement (fig. 4, 7), the difference in the strain degree over the diameter of all bars is not more than 10 %. Fig. 8 shows the steady stage of angular pressing and the pressed bars as the three-dimensional representation with a strain field when the die channels are arranged along the axis of the rectangular groove (fig. 8, a) and along the radius of the container (fig. 8, b). It turns out that in both variants of the process the maximum strain degree can reach the value of 2.6 at the initial stage, before the stationary deformation zone is formed, and 5.0 at the steady stage. The strain degree in both variants reaches its maximum value at a considerable distance from the front ends of the bars. Thus, the front ends of the bars may be not sufficiently structured. It is also worth mentioning that with the die channel axes arranged as per fig. 8, a the strain along the length of the bars is less than with the die channel axes arranged as per fig. 8, b. On average, the difference reaches 20 %. Besides, when the die channel axes are arranged along the container radius (fig. 8, b), it is apparent that the strain distribution along the length of the bars is more uniform as compared to pressing through the die with its channel axes arranged along the axis of the rectangular groove (fig. 8, a).
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