Influencing forming forces and springback during incremental profile forming using stress superposition

Abstract

Incremental processes allow the production of variable geometries through the sequencing of local forming operations. This high flexibility is accompanied by complex springback and low dimensional accuracy. Dimensional accuracy basically increases with reduced forming forces. In this paper, the influence of stress superposition on process forces and dimensional accuracy in incremental profile forming is investigated. As a fundamental incremental forming process, radial indentation into a tube without axial infeed of the tube is considered. The radial depth of indentation is 6 mm. A spherical tool (R = 4 mm) is used as the forming tool. The tube materials used are X5CrNi18-10 and X2CrTiNb18 and E235N steels in a normalized state (σ_{0,X5CrNi18–10} = 406 MPa, σ_0,X2CrTiNb18 = 412 MPa, σ_0,E235 = 300 MPa) with a wall thickness of 1.5 mm. The tube diameters is 40 mm. The numerical modeling of the process is performed in Abaqus/Standard (implicit). Axial tension is applied for stress superposition. The amount of superposition varies from 50 to 100 % of the yield stress. The results show that for each level of superposed axial stress, the forming force is reduced over the no-axial-stress case. This is accompanied by a reduced springback of the tube. Furthermore, the localization of the forming zone can be influenced by stress superposition, whereby axial tensile stress enlarges the forming zone.