A study of forming of thin-walled hemispheres by mandrel-free spinning of commercially pure aluminum tubes

Abstract The purpose of this research is to understand the effect of process parameters in multi-pass, mandrel-free, room-temperature tube-spinning, and in particular the role of axial feed-rate on the shape and thickness change when producing a hemisphere. This is tackled with a combination of experiments and analysis. The material of this study is heat-treated, commercially-pure aluminum (AA1070) tubes of 100 mm diameter. To produce the hemisphere, seven linear passes are selected. The spinning experiments are conducted for two tube thicknesses (2 mm and 3 mm) under three different axial feed-rates (2, 5, and 7.5 mm/rev.) and identical radial feed-rate (5 mm/pass). It is found that decreasing the axial feed-rate generates less spatial variation in the final thickness, while also making the process slower. During every experiment, the tube wrinkles axially. The experiments are interrupted after different spinning passes, and the shape and thickness are measured. Three different finite element models are described, using axisymmetric, shell and solid elements, respectively. Comparing them to the experiments shows that the computationally-efficient axisymmetric model gives reasonable shape and thickness predictions. The shell element model tends to overpredict the shape and thickness evolution during spinning, while being about 250 times slower. Finally, the solid element model provides good agreement with the experiments across the board, while being only 2 times slower than the shell element one. Hence it is recommended for industrial practice to use the axisymmetric model for preliminary process design (i.e., selection of toolpath and process parameters) and then to refine these selections with the solid element model.