Investigation of the circumferential distortion and formability of 6061 aluminum alloy tubes in stagger spinning with a larger initial thickness blank

Stagger spinning is an efficient method to fabricate thin-walled tubular parts, especially for large thinning amount with a larger initial thickness blank, but the appropriate control of process parameters and the flow deformation of the contact zones need to be further studied, so as to achieve the accurate forming and performance improvement of as-spun tubes. The influence of stagger distance, thinning rate and spinning pass on the dimensional accuracy, mechanical properties, metal flow and circumferential distortion of as-spun tubes in multi-pass stagger spinning were investigated through the FE simulation and process experiment. The high precision thin-walled tube can be obtained by designing appropriate thinning rate and multi-pass stagger spinning with a larger initial thickness blank. When the total thinning rate reaches 72.8% after 6 passes spinning, the thickness and radius deviation of the 6061 aluminum alloy tube are 0.042 mm and 0.01 mm, respectively. The yield strength of the tubes in the axial direction is larger than that in the circumferential direction after each pass and the difference increases with the spinning pass. The increase of spinning pass is contributing to the improvement of axial performance. The initial axial node line on the surface of tube is deflected to the spiral and the deflection angle is consistent with the roller rotating direction. The shear strain ε_τz in τ-z plane and ε_rτ in r-τ plane of the contact zone leads to the obvious circumferential distortion. The shear deformation in the τ-z plane of the contact zone is close to the typical simple shear mode. There is a decreasing gradient shear deformation in the r-τ plane from the outer layer to the inner layer, which leads to the difference of the circumferential twist deflection distance between the inner and outer surface of the as-spun tube.