Abstract: Cryogenic forming has been developed into a revolutionary technology for forming alloy thin-walled components recently. The dimensional accuracy of cryogenically formed components is significantly affected by the temperature distribution and complex loading conditions. Therefore, the springback of aluminum alloy spherical shell was studied under different temperature distributions. The control mechanism of gradient temperature fields on springback was revealed through an analysis of deformation uniformity and stress. The results show that the springback of the spherical shell decreases with an increase in the temperature gradient. The dimensional deviation in the opening region decreases from 1.35 mm to 0.83 mm as the temperature gradient increases from 36 ℃ to 216 ℃, showing an enhancement in corresponding dimensional accuracy of 38.5%. This is because of the significantly improved stress gradient and deformation uniformity. On the one hand, stress gradient is increased to transfer the deformation of the unsupported region, and the stress difference is reduced in the spherical shell region. On the other hand, the deformation becomes more uniform as the temperature gradient increases, with the average deviation rate of thickness improved by 55.8% in the entire spherical shell. Among them, the maximum thinning rate in the spherical shell area was reduced by 36.9%, and the maximum thickening in the flange region was reduced by 74.6%. Cryogenic forming can not only significantly improve the forming limit of aluminum alloy but also reduce springback and improve the dimensional accuracy of the components by increasing the temperature gradient. The results can provide guidance for the dimensional accuracy control of spherical shells in cryogenic forming.

Key words: aluminum alloy, cryogenic forming, spherical shell, springback, theoretical analysis