Hydroforming of a stainless steel T-joint with ratio of tube diameter to thickness D/t = 108 and ratio of branch diameter to tube diameter d/D = 0.6 was studied. The effects of counter punch loading path on branch height and thickness were discussed. Because the branch diameter is smaller than the tube diameter, it is difficult to obtain a higher branch height and avoid thinning at the same time. An approach for increasing branch height of a hydroforming T-joint with smaller branch diameter was proposed. Finite element method (FEM) simulations were carried out for analyzing the deformation during hydroforming of the T-joint. Thinning ratio distribution, stress and strain states from different loading paths were presented. The experimental results show that the new approach with counter punch moving backwards during calibration is effective to increase branch height and to improve thickness distribution.

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