Control and use of wrinkles in tube hydroforming

The common defects in tube hydroforming are buckling, bursting and wrinkling. Wrinkling occurs as the axial force reaches a critical value, which was considered as one of defects in the past. In this paper, theoretical analyses, numerical simulation and experiment were conducted to investigate wrinkling behavior in tube hydroforming and how to control and use wrinkles. Effect of loading path and length to diameter ratio on the number of wrinkles and part shape is discussed. It has been shown from the research results that not all wrinkles are defects and tube can be successfully formed after wrinkling in some cases. The key issue is obtaining useful wrinkles instead of dead wrinkles. However, the thickness distribution is not even along the longitudinal direction. Accumulation of material in the expanding area by formation of wrinkles is an effective method for obtaining preform. By use of this method, process window can be enlarged for hydroforming.