REFORMING INTERNAL PRESSURE AND AXIAL FEEDING LOADING PATHS IN HYDROFORMING PROCESS OF CYLINDRICAL STEPPED TUBE IN ORDER TO IMPROVE THE THICKNESS DISTRIBUTION

Internal pressure and axial feeding are the most important factors in tube hydroforming process. The internal fluid pressure and the material feeding that is produced by punch axial loading form the tube. How to apply these two parameters simultaneously in combination has effects on the quality, thickness and forming limit of the final piece. In this paper, the effects of internal pressure and axial feeding paths were investigated to improve the thickness distribution of stepped cylindrical tubes and the wrinkles in the loading path were used to create a new method for removing the wrinkles. Firstly, the constant pressure loading paths with various pressure levels were investigated. Then, the pressure levels in which the parts weren’t burst and formed perfectly or formed with wrinkles were chosen and the effect of axial feeding on these paths were examined separately. The results showed that the axial feeding in the initial step of increasing pressure improves the part thickness distribution in final step. In addition, through using this new method, the wrinkles on tube body were eliminated at the end of the process by changing the direction of axial feeding, and consequently the sound part with better thickness was obtained. Furthermore, using stepped loading path improved thickness distribution uniformity through applying this new method of wrinkle elimination.