Deformation-based joining for high-strength Ti-3Al-2.5V tubular fittings based on internal roller swaging

Deformation-based joining presents efficient, reliable and environmentally friendly advantages widely applying in the pipeline system. Internal roller swaging (IRS), one of deformation-based joining ways, is an inner expanding spinning process with characteristics of sheet-bulk forming, and it has the potential to fabricate high-strength tubular joining components with better high-pressure resistance and sealing performance. Taking a high-strength Ti-3Al-2.5V titanium alloy (TA) tube as the case material, this study combines explicit and implicit finite element (FE) modeling with experimental validating to explore the deformation mechanisms of the IRS process. By using the digital image correlation method (DICM) based uniaxial tension, the contractile strain ratio (CSR) of the TA tube was obtained to describe its anisotropy. By analyzing the mechanism of IRS, the motion equations of three rollers were deduced in the forming process, and a simplified 3D FE model for the IRS process was developed. Based on the FE simulation and analysis, the inhomogeneous flow deformation behaviors of TA tube in the IRS process were investigated by subdividing the deformation areas of the tube. Then, the material flow features of TA tube in the IRS process were explored by analyzing the axial displacements of the tube and observing its flow localization by means of optical microscope. Finally, the forming quality of the tubular joining components can be accurately designed and controlled by revealing the relationship between the swaging depth and the axial elongation and the relationship between the swaging depth and the contact shear stress. It is concluded that this incremental deformation-based joining process has obvious superiority to fabricate high-strength TA tubular joining components, and their reliability can be effectively enhanced by accurately controlling the swaging depth.