Numerical simulation and buckling analysis of tube external pressure forming

In the external pressure forming process, a tubular part can be formed onto a mandrel in the tube blank by external hydraulic pressure. During the forming process, the cross-section of the tube blank is reduced and the inner side of the tube is pressed onto the surface of the mandrel so that the formed part has a precision inner contour corresponding with the mandrel. Finite element method was applied to analyze the main factors affecting buckling deformation features and forming process. Reducing the length of the tube causes an increase in the number of circumferential buckles and a decrease in the critical buckling pressure. Increasing the wall thickness leads to a reduction in the number of buckles and an increase in the critical buckling pressure. In addition, for a tube blank with a certain shape defect, the critical buckling pressure is much lower than that of a perfect circular-cross-section tube. However, the defect has no significant effect on the forming result.