Friction plays an important role in the corner filling behavior during hydro-forming of rectangular section. In order to study the variation in corner filling behavior with internal pressure under the condition of different coefficients of friction, Gurson-Tvergaard-Needleman ductile damage model was used to describe material deformation involving damage evolution. First, an experimental-numerical hybrid method was applied to determine the parameters of critical porosity and failure porosity in Gurson-Tvergaard-Needleman ductile damage model. Second, a model describing the deformation behavior was established, in which the deformation zone was divided into three parts: sticking zone, sliding zone and corner zone. Third, the effect of coefficient of friction on the corner filling process was studied through simulation and experiments. The results show that as the internal pressure increases, the sticking zone starts at certain pressure and increases rapidly until taking over the whole contact length. Sticking friction will lead to greater thinning, and bursting occurs rapidly at the transition zone. Furthermore, the increase in the coefficient of friction will lead to greater variation in thinning and corner radius. For m = 0.05 in experiments, corner filling is acceptable without bursting, correspondingly the final internal pressure is 67 MPa.
Abstract. Control and use of wrinkles is a challenge in tube hydroforming because wrinkle was always considered as one of the defects of tubes from the traditional view. In this paper, a dedicated experimental setup was designed and manufactured, using which the investigation of wrinkling behavior coupled with internal and external pressure can be realized. The effect of internal or external pressure on 5A02 aluminum alloy tubes and 0Cr18Ni9 stainless steel tubes were all investigated using this setup. It was found that the number and shape of wrinkles are strongly dependent on the internal or external pressure. More important is that the geometrical configuration of wrinkles can be perfectly characterized using the Gauss function rather than the sine function adopted in the published literature. In addition, the fitted Gauss functions for every wrinkle were integrated in order to compare their area with the corresponding area of die cavity, so as to obtain the appropriate process parameters for the useful wrinkle, which can be formed in advance and then flatted in the calibration stage.
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