Die filling mechanism in flow forming of thin-walled tubular parts with cross inner ribs

Flow forming is a promising technique to manufacture thin-walled tubular parts with cross inner ribs (longitudinal and transverse inner ribs, LTIRs) which are highly demanded in aerospace field. However, the nature of local loading results in complicated material flow and consequently affects the formation of inner ribs by die filling. Therefore, flow forming experiment along with finite element (FE) simulation was carried out to study the material flowing behavior in the flow forming of stiffened parts, thus to reveal the die filling mechanism. The results showed that varied rib height occurred after flow forming on account of the different die filling mechanisms of longitudinal inner ribs (LIRs) and transverse inner ribs (TIRs). Namely, the axial tensile strain results in a low LIR, while it is a nearly plane strain state for TIR and the radial tensile strain in the inner layer of TIR is in charge of the larger TIR height. In order to improve the rib height, large wall thickness reduction and feed ratio should be used. The law of die filling in flow forming of thin-walled tubular parts with LTIRs will provide guidance for the integrated manufacture of stiffened thin-walled tubular parts in a high quality.