Experimental Investigation of Maximum Achievable Convolution Height of Metallic Bellows in Hydroforming Process

The manufacturing of metal bellows with high ratios of crown-to-root diameters is very sensitive to design parameters such as internal pressure inside the tube, axial force and movement, die-stroke length (distance of the dies) as well as the initial tube length. In this paper, hydroforming process of a metallic bellows is investigated experimentally. For this purpose, the effects of internal pressure and die stroke on the maximum achievable convolution height and thickness distribution of hydroformed bellows is studied. The experiments are performed with different internal pressures such as 90, 110 and 130 bars and also in different die strokes such as 10, 12 and 14 mm. The results show that by increasing the die stroke, the range of allowable internal pressure to produce a metallic bellows without wrinkling or bursting decreases and manufacturing of the bellows becomes more difficult. It is extracted from results that with holding the die stroke value, very low internal pressures lead to wrinkling in the hydroformed bellows while very high internal pressures cause the excessive thinning. Also, it is concluded that by increasing both internal pressure and die stroke, the convolution height of manufactured bellows is increased. It is proved that the maximum thickness reduction is occurred at the crown point of hydroformed bellows.