Research on deformation law of hydroforming steel/aluminium double-layered tubes

Hydroforming process of double-layered tube is proposed to solve the wrinkling encountered in manufacturing the ultra thin elbows with traditional bending processes. The numerical simulation of hydroforming of carbon steel/aluminium alloy double-layered tubes were conducted to investigate the influences of internal pressure and thickness ratio on wrinkling and wall thickness distribution of the double-layered tube. It is shown that the maximum wall thinning of the outer elbow decreases and the wrinkling eliminates as the thickness ratio increases, which implies a uniform wall thickness distribution. With inner pressure increases, the inner thinning rate decrease gradually, and the wrinkling was delayed. So increase thickness ratio and pressure are helpful to improve the stability of double-layered tube. The hydro-bending experiments are carried out to obtain successfully the thin-walled elbow tubes with bending angle is 70°. The outer maximum thinning rate was 24%. Results proved that double-layered tubes hydroforming is suitable for manufacturing large diameter-thick ratio of ultra thin-walled tube.