Hydraulic Bulging and Failure Analyses of Wire Arc Additive Manufactured Steel Tubes

In the present work, formability and failure of wire arc additive manufactured (WAAM) tubes during hydraulic bulging were analyzed to understand the feasibility of forming printed components under bi-axial stress state. Tubular components of length 250 mm were printed using a gas metal arc welding-based WAAM setup, and these tubes were machined to achieve an outer diameter of 42 mm with wall thickness of 1.5 mm. Predominantly ferritic and pearlitic microstructure was witnessed along the build direction (BD) of the tubes with differences in grain size. Tensile testing along different directions to BD of tubes revealed anisotropy with excellent strength and ductility. Subsequently, tubes of length-to-diameter ratio of 3 were deformed using an indigenously developed hydraulic tube bulging setup. It was observed that printed tubes underwent plane strain deformation path and fractured at 27 MPa pressure after attaining the height of 6.1 ± 0.42 mm. The circumferential strain and thickness distributions of fractured tubes suggested a non-uniform deformation during bulging. Upon further investigation, it was found that the presence of anisotropy and initial porosity in printed tubes led to this non-uniform deformation. Based on x-ray micro-computer tomography scan and fractography analysis, it was observed that the pores present in printed tubes were spherical, which assisted in sustaining high plastic deformation and reduced the chances of premature failure. The above findings suggest that tubular components with different features can be fabricated through hybrid manufacturing coupling WAAM with sheet metal forming processes.