IMPROVEMENT OF THE METHOD OF CONSTRUCTING LIMIT DEFORMATION CURVES FOR ROLL STAMPING PROCESSES

The analysis of the construction of the curves of limit deformations of metals is carried out in the work. It was established that traditional methods of testing, such as deposition and stretching of cylindrical samples, do not ensure constancy of the stress state indicator, and therefore introduce the history of deformation into the construction of curves. During deposition, there is an increase in the stress state indicator due to the curvature of the side surface of the sample (the formation of a barrel), which is caused by friction on the ends. And during stretching, the stress state indicator also increases, as a result of the formation of a neck due to the loss of deformation resistance. Therefore, measures were considered that would ensure obtaining reliable results when constructing the curves of limit deformations excluding the influence of deformation history. During deposition, such measures include the use of a plastic foil, softer than the sample material, on the ends of the samples and stepwise removal of the edges of the hole on their ends by grinding or deposition without foil. In addition, an experimental and computational method was considered, which involves the construction of deformation paths and correction of the limit deformation using the deformability criterion. During stretching, in the case of neck formation, the increase in deformation depends linearly on the ratio of the radius of curvature of the neck to its diameter. An equation is presented, which can be used to take into account the influence of the neck parameters on the increase in limit deformations using the experimental and computational method. For the experimental determination of the ultimate deformation during stretching, a method of rolling cylindrical samples into a wedge with rolls, the radii of which increase during the rolling process, which allows to eliminate the appearance of a neck, is proposed. With sufficient accuracy for practice, the curves of limit deformations can be constructed based on the results of testing samples for torsion and sedimentation, and the values of limit deformations during stretching can be obtained using approximating dependencies tested for various metals. According to the above method, including the determination of plasticity by rolling, the curves of limit deformations of a number of steels were constructed.