OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 a b Fig. 3. The initial assembly of the tool (the container is currently transparent) and the blank in the XZ plane for the simulation option when using a die with the axes of the channels along the axis of the rectangular groove (a) and along the radius of the container (b) The formulation of both variants of the problems consisted of entering data on physical and plastic properties of the blank metal, as well as in description of the shape of the deformation zone. The magnesium blank has a cylindrical shape (diameter D = 40 mm and height H = 42 mm). The boundary friction conditions are set by Siebel law (the friction coefficient is 0.2). The condition for stopping the calculation is set by the movement of the punch along the z-axis by 28 mm. In this case, a discard 14 mm high will remain in the container. The computational formulation is described as follows: the deformable medium is ductile; the type of a task is isothermal (the temperature of the blank and the tool is 20 °C); the number of finite elements of the blank at the initial moment of time is 50,000; the tool is assumed as a rigid body. Fig. 3 shows the initial assembly of the tool (the container is at this point is transparent) and the blank in the XZ plane for the two variants of the models: 1) when the die channel axes are positioned along the axis of the rectangular groove (fig. 3, a) and 2) when the die channel axes are positioned along the radius of the container (fig. 3, b). Results and discussion Fig. 4, a shows the result of solving the task in the form of mean stress distribution at the steady stage of angular pressing as the three-dimensional representation when using the die with channel axes arranged along the axis of the rectangular groove. Fig. 4b shows the same, only for the die channel axes arranged along the radius of the container. It can be seen that the cylindrical blank in the process of deformation is under the action of mean (hydrostatic) compressive stresses at the level of -1,600 MPa. Thus, an all-round compression behavior is provided here, and the presence of high (modulo) values of the mean stress allows us to expect an increase in the level of ductility, which should prevent metal fracture. The pressure on the punch in this process is presented in fig. 5, a for the die channel axes arranged along the axis of the rectangular groove and in fig. 5, b for the die channel axes arranged along the radius of the container. In this case, a reference point for the adequacy of the pressure on the punch can be the specific pressure on the punch during NECAP of a strip with a similar elongation ratio. It is known [28] that in this case it is equal to 1,300 MPa, which means that the value of 1,400 MPa obtained in this solution is quite probable. Fig. 6, a shows the result of solving the problem in the form of regions of equal level of strain rate in the steady stage of angular pressing for the longitudinal section of the central bar in the YZ plane when using the die with the arrangement of the channel axes along the axis of the rectangular groove. Fig. 6, b shows the same, but for die channel axes arranged along the container radius.
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