Calculation of Residual Stress and Parameters of Sheet Springing on a Roller Leveler

Most technological processes of metal products manufactured by plastic deformation methods are associated with the formation of a self-balanced system of residual stresses in finished products. In many cases, the level of residual stresses is an important parameter that determines the product quality obtained as a result of plastic deformation. Reasons for the formation of residual stresses are diverse (inhomogeneity of plastic deformation, temperature field, phase transformations, etc.), which in their magnitude can exceed stresses from external loads. Currently, additional requirements are imposed on metal products in order to create machines and structures operating under high loads and speeds, sharp fluctuations in the parameters of the external environment. The experience of operating structures in various fields of technology and the results of numerous experiments show that residual stresses significantly affect the reliability and durability of machines and mechanisms. Based on the A.A. Ilyushin theory of unloading, analytical dependences were obtained for calculating the diagram of the change in residual stresses across the sheet thickness during bending under the rollers of leveler, as well as the springing angle. The diagram formation of residual stresses along the sheet thickness during leveling for the second, third and subsequent rollers of the leveler is considered. As a result of the superposition principle, it was found that the residual stress diagrams under the second and third rollers are added, forming a total diagram after the second and third rollers. For the fourth, fifth, sixth and subsequent leveler rollers, an algebraic addition of the residual stress diagrams also occurs. It is shown that for a 45 steel sheet with a thickness of 10 mm, a width of 500 mm, r / h = 200, the maximum residual tensile stress of 200 MPa is observed at a distance of Z / h = 0.3 from the neutral line along the sheet thickness. And in this case, the discrepancy between the experimental and calculated values of residual stresses is 10 –26 %, which makes it possible to recommend a method for calculating the residual stresses when leveling a sheet on a roller leveler for estimation of its quality.