2019 Volume 60 Issue 704 Pages 268-273
Recently, tube hydroforming is appreciated for its contribution to improving fuel economy and crash safety. For further complex shapes, sheet hydroforming has some advantages because sheet blank shape can be designed freely. In this paper, the basic forming characteristics of punchless sheet hydroforming are investigated on the basis of the results of experiments and finite element (FE) analysis. The main conclusions are as follows. (1) In hydroforming, panel dent resistance is improved compared with that in stamping, because larger strain can be induced and work hardening occurs in the punch bottom area in hydroforming. (2) Fractures and wrinkles occur in the stamping drawing test. On the other hand, wrinkles do not occur in the hydroforming drawing test, because, in hydroforming, circumferential stress at the lower area of the side wall shifts in the tensile direction compared with that in stamping and sheets are supported by internal pressure, which suppresses the out-of-plane deformation. (3) The formable range of the drawing test in hydroforming is greater than that in stamping, since relatively large strain can be induced in the entire specimen in the equibiaxial strain state in hydroforming.
