A new method for hydroforming of thin-walled spherical parts using overlapping tubular blanks

Tube hydroforming is an advanced metal forming processes, which is widely used to form various tubular parts. Axial feeding is usually used to avoid excessive thinning in hydroforming of a variable-diameter part. However, wrinkling defects are susceptible to occur easily under the axial loading if the wall thickness of the tube is small. A new method was proposed to enhance the expansion ratio and improve the thickness distribution for hydroforming of thin-walled spherical parts using overlapping tubular blanks. A special loading tool was created and AISI 304 stainless steel blanks were used for the experimental research. The effects of blank shapes and normal constraints were studied on wrinkling defects of the overlapping blanks. The results show that wrinkling defects at the inner layer of the overlap are prevented by using curved-edge blanks. Wrinkling defects at the outer layer of the overlap is eliminated by using normal constraints. Finally, a sound thin-walled spherical part was obtained by using an overlapping tubular blank. The maximum expansion ratio is 60% and increased by 30.2% compared with that of conventional hydroforming using a closed cross-sections tube. The maximum thinning ratio was 32.4%, which was decreased by 29.3%. In general, it is feasible to use an overlapping blank to form a variable diameter part. The maximum expansion enhances significantly and the thickness distribution improves apparently.