Experimental and numerical investigation of hydroforming process of bi-layered metallic bellows

In this paper, hydroforming process of bi-layered bellows is investigated experimentally and numerically. The process consists of two steps: tube bulging and tube folding. For this purpose, the effects of two main process parameters i.e. internal pressure and die stroke on characterizations of hydroformed bi-layered bellows are examined. The convolution height and thickness of the top point of each convolution are selected as the main features of metallic bellows. The results show that the numerical simulations are in good agreement with experimental measurements. It is demonstrated from the obtained numerical and experimental results that the thickness reduction is noticeably increased from bottom point to top point of each convolution. In addition, it is concluded that the inner layer has the most reduction in wall thickness while the outer layer has the least thickness reduction due to the supportive role of the inner layer for the outer layer. The experimental and numerical results showed that a bi-layered bellows can successfully fabricated with internal pressure of 230 Bar and die stroke of 14 mm. Also, by changing the internal pressure from 70 to 230 Bar in a situation where the die stroke is constant and equal to 14 mm, the convolution height will increase by about 62% while the thickness of top point of outer layer will decrease by about 20%. Changing the die stroke from 6 to 16 mm in a situation where the internal pressure is constant and equal to 230 bar leads to a 60% increase in the convolution height and a 23% decrease in the thickness of top point of outer layer.