New strategy for process parameters optimisation in tube hydroforming of T-joints

Tube hydroforming process is a forming technique that consists of tubular workpiece deformation by means of hydraulic pressure and punches which guarantee the tube end feeding and sealing. In the last years, this technique found a large and rapid development thanks to its many advantages with respect to conventional processes: parts weight reduction, tighter dimensional tolerances, lower tool and die costs, less secondary operations. Besides, many lacks in the process knowledge still represent an obstacle and they are usually bypassed by trial and error methods. Therefore, lot of studies have been conducted to better understand the influence of the process parameters, such as pressure path, punch stroke or material behaviour on the process feasibility. In this paper a finite element model, validated by means of experimental tests conducted on a self designed hydroforming machine, was used for forecasting initiation and growth of defects in T-joints hydroforming. The conducted finite element analysis allowed to identify the aspects of the process which cause defects in tube hydroforming of T-joints. In this manner performance indicators to be used for developing a process optimising strategy were identified.