Evaluation of the bars’ multichannel angular pressing scheme and its potential application in practice

Abstract

Introduction. Deformation of low-plastic materials requires a high degree of compressive stress. This requirement is implemented, for example, in the process of equal channel angular pressing (ECAP). However, the products obtained by the ECAP method have a cross-section identical to the initial blank, which is one of the disadvantages of this method. The method of nonequal channel angular pressing (NECAP), in contrast to ECAP, makes it possible to change the shape of the initial blank towards closer to the shape of the finished product. However, the well-known NECAP device allows obtaining products only in the form of a thin strip of rectangular cross-section. Well-known devices for multichannel pressing of non-angular type also have a disadvantage — it is implemented only on horizontal type presses, where it is possible to receive long products on the workshop areas. The aim of the work is the evaluation of the bars’ multichannel angular pressing scheme, combining a change in the shape of the initial workpiece in cross-section, as well as the accumulation of a high level of strain during deformation. Research methods: finite element modeling using the DEFORM software module. Results and discussion. The paper considers the scheme of the angular pressing process with the use of a device that allows, for example, to obtain magnesium bars with a diameter of d = 4.1 mm with the number of matrix channels n = 3 from a blank of round cross-section. The container of this device in its lower part has a rectangular groove where the matrix is inserted. Modeling of the process under study using a matrix with the axes of its channels located in the plane of the orthogonal axis of the container and, in the first variant, along the axis of a rectangular groove, and in the second variant, along the radius of the container, allowed us to estimate the distribution of the average stress. It is established that the metal of the blank in both variants of the deformation process is affected by compression stresses at a high level (1,600 MPa). The assessment of the degree of deformation of the pressed bars allowed us to find out that at the initial stage of both process variants, the maximum strain degree can reach 2.6, and at the steady stage it reaches 5.0. It is established that in the case of the first variant of the matrix, the strain level along the length of the bars is lower than when using the second variant of the matrix. The difference reaches 20 %. By evaluating the distribution of the strain degree in the cross section of the pressed bars near the deformation site, it was found that in the case of the first variant of the matrix, the pressed bars of the first and third channels have an uneven dimensions, and the greater value of the strain degree is on the peripheral part of the rods from the side bordering the central bar. This difference in the strain degree reaches 20 %. When placing the second version of the matrix, this unevenness decreases to 12 %. Thus, in the case of using a matrix with the arrangement of the channel axes along the radius of the container, the strain degree is distributed more evenly compared to the strain degree when using a matrix with the arrangement of the channel axes along the axis of a rectangular groove.