Investigation of Changes in the Resistance to Deformation of Low-Carbon Steel in the Process of Flow Forming

Abstract

Introduction. The main parameter that determines the efficiency and quality of the flow forming is the value and nature of the distribution of the material’s deformation resistance over the wall thickness of the workpiece. In the technical literature, devoted to the study of this process, there is not enough information to correctly assign technological regimes and processing conditions. The work is devoted to an experimental study of changes in the resistance of deformation of low carbon steel in the process of flow forming, depending on the degree of deformation and the angle of taper of the deforming roller. The aim of the work is to determine the non-uniform distribution of the resistance of the deformation of low-carbon steel through the thickness of the wall of the workpiece after the flow forming depending on the degree of deformation and the angle of taper of the deforming roller. Research methods. The process of flow forming of blanks having an initial wall thickness of 6.5 mm and an outer diameter of 203 mm is carried out on a three-roller horizontal-rolling machine SRG-0.6-1500 using a direct method. Plastic shaping of the material of the blanks is carried out at different degrees of deformation on the mandrel with a diameter of 190 mm deforming rollers with a diameter of 260 mm with an angle of taper equal to 20 ° and 30 °. The deformation resistance of the material through the wall thickness is determined on longitudinal specimens cut from machined blanks using the indenter insertion method and measuring the hardness with a Vickers tip. The uneven distribution of the strain resistance is estimated by a coefficient defined as the ratio of the resistance of the deformation of the outer surface to the resistance of the deformation of the internal volumes of the wall of the workpiece. Results and discussion. The highest values of strain resistance are obtained on the outer surface of the workpieces treated with a roller, and the smallest values are recorded in the internal volume of the wall of the workpieces. The estimation of the non-uniformity of the distribution of the deformation resistance over the wall thickness of the workpiece is made using an irregularity coefficient equal to the ratio of the deformation resistances of the outer layer and the internal volumes of the wall of the workpiece. It is revealed that the most dangerous zones subjected to destruction in the process of rotational drawing are the internal volumes of the material adjacent to the outer surface layer of the workpiece. It is established that the non-uniformity coefficient of stress distribution when processing with a roller with a taper angle α = 30 ° is about 10% more than with a taper angle α = 20 °. With an increase in the degree of deformation, the coefficient of uneven distribution of stresses increases, but very slightly. The resulting patterns are explained, in particular, by the influx that forms in front of the roller. According to the results obtained, general recommendations are given on the purpose of the degree of deformation and the angle of taper of the roller when performing the flow forming. In addition, the empirical dependences of the strain hardening of the material for different volumes of the workpiece are obtained. The proposed method for determining the uneven distribution of stresses can be used in the development of pressure treatment processes and in the design calculations of structural elements. © 2019 The Authors. Published by Novosibirsk State Technical University.