As a process for producing seamless tubes, the tandem skew rolling (TSR) process was proposed. In order to study deformation characteristics and mechanism on tubes obtained by the TSR process, a numerical simulation of the process was analyzed using Deform-3D software. Simulation results demonstrated the distribution of stress, strain, velocity, and temperature of a seamless tube in the stable stage during the TSR process. Actual experiments of carbon steel 1045, high strength steel 42CrMo, and magnesium alloy AZ31 were carried out in a TSR testing mill. The results demonstrated that the TSR process is qualified for producing tubes of high quality, with an accuracy of ±0.2 mm in wall thickness and ±0.35 mm in diameter. This process is suitable for manufacturing seamless tubes that are difficult to deform or that have been deformed in a narrow range of temperature.

Tube continuous rolling (TCR) is a beneficial method for the production of titanium pipes due to its high efficiency and shorter process, with the mandrel playing a crucial role. The present study delved into the mechanism of the mandrel and its impact on the TCR process, through comprehensive analyses that included numerical simulations and experimental tests. The following conclusions were drawn: as the mandrel diameter coefficient increases, the area of the front slip zone gradually expands, and the tension changes from tensile stress to compressive stress. Additionally, the temperature exhibited an overall downward trend, while the strain distribution at the groove vertex and taper became more uneven. Concerning metallographic structure, instances where the mandrel diameter coefficient increases led to elongated, recrystallized grains at the groove vertex. The twinning quantity at the groove taper increased initially and then decreased, indicating a deformation mechanism shift from twinning to slip.

The continuous retained-mandrel rolling process is a promising method for titanium tube production with high efficiency and a short process. The importance of mandrel as a deformation tool supporting the inner wall is crucial. This paper thoroughly examines the influence of mandrel velocity on the deformation characteristics at the groove vertex using three approaches: numerical simulation, shear-deformation observation experiments, and microstructure analysis. The following conclusions are drawn: Decreasing the mandrel velocity enhances the penetration of shear deformation into the inner wall of the titanium tube, improves thickness uniformity, and shifts the deformation mechanism near the inner wall from twinning to dislocation slip. As a result, the volume fraction of recrystallization increases from 18.4% to 42.3%. However, the mean shear strain increases first and then decreases to a certain value as the mandrel speed decreases, which is attributed to the combined influence of the cross-shear zone and the rolling force.