A Springback Prediction Model for Warm Forming of Aluminum Alloy Sheets Using Tangential Stresses on a Cross-Section of Sheet

Abstract

Warm U-draw bending tests were performed on a 5182 aluminum alloy under isothermal and non-isothermal conditions, and the amounts of springback under the corresponding conditions were measured. Finite element method analyses were then conducted to calculate the tangential stress distribution on the cross-section of the sheet during the warm forming process. It was found that the experimentally measured springback values were proportionally related to the differences in the amounts of tangential stresses at the top and bottom layers of the sheet section. A functional model that can account for the correlation between the amount of springback and the difference in tangential stresses at the top and bottom layers of the sheet section was derived based on an Euler beam and a nonlinear flow stress model with temperature and strain rate dependencies. The developed model, which can predict springback behavior using only results of forming analyses of warm formed aluminum alloy sheets, is anticipated to provide for advancements in the understanding of springback behavior at warm temperatures and improve the efficiency of design and analysis processes used to fabricate parts with complicated shapes by saving considerable time and costs for the analysis of springback.

An Adaptive Algorithm and Additively Manufactured Punch Used to Form Aluminum Sheet Metal Parts

“…Changes in the part’s shape appear after the forming forces act. Different specific factors and parameters also influence the metal parts, resulting from various forming processes [ 1 , 2 ]. The deformation of any element can be described based on the β ratio between the strains or the α ratio between the stresses.…”

“…The most important phenomenon in the instability of the shape and dimensions of the sheet metal parts, obtained by cold plastic forming, is the springback phenomenon specific to both bending and drawing processes [ 1 , 2 ]. The springback in the cold plastic forming of the sheet metals is given by the difference between the final shape of the part and the shape obtained at the end of the punch stroke.…”

“…Because the phenomenon of springback is favored by the material’s elastic properties, any factor that decreases the ratio between elastic and plastic strain determines the reduction in the springback intensity. Therefore, materials with a lower yield strength and Young’s modulus, higher hardening, a normal anisotropy index, a higher clamping force value, a different punch geometry, or a lubricated environment between the die and the sheet metals can reduce the intensity of the phenomenon [ 1 , 2 , 6 , 7 , 8 , 9 , 14 , 15 ].…”

“…Therefore, the tools specific to the plastic forming process can be man specific way to satisfy the requirements to decrease the intensity of the spr The rebound process is elastic, but a secondary plastic flow can also occur due to the bending and straightening around the edges of the die and punch. When metal sheets are bent, springback is manifested by the angle change and the formed part's curvature [1,2,[6][7][8]. The parameters that characterize the effect of springback are the springback angle θ and the radius of curvature R after the rebound.…”