Theoretical and experimental analysis of stroke-controlled tube hydroforming

To select tube hydroforming instead of conventional fabrication, one has to know the tube material behaviour and tribological effects during hydroforming and how the hydroforming operation itself should be controlled. The hydroforming operation is either force- or stroke-controlled. This paper deals with stroke-controlled hydroforming. Hydroforming consists of free forming and calibration. In this paper, only the so-called free forming is treated. Stroke-controlled free forming is studied theoretically and experimentally. The theoretical part consists of analytical modeling and finite-element simulations. The conducted experiments are used to show the types of errors that might occur, when the theoretically obtained loading paths are transferred to the hydroforming equipment. The forming limit curve (FLC) is normally used as an aid/instrument in component and process design (which include finite-element simulations). The present study shows that the FLC of the tube material must be determined by hydroforming, if component and process design are to rely on this instrument.