Xiaosong Wang

Experimental and numerical investigation into useful wrinkling during aluminium alloy internal high-pressure forming

Abstract Internal high-pressure forming is a process for manufacturing lightweight components, especially automotive parts, with advantages of lower cost and weight reduction, better structural integrity and increased strength and stiffness over the conventional stamping process. One of the typical failure modes, including wrinkling, buckling and splitting, will occur through an unreasonable combination of the control parameters: the internal pressure and the axial punch feeding. In most previous papers, wrinkling is considered to be a failure mode. However, not all wrinkles are defects. The collection of materials in an expanding area by the formation of wrinkles is an alternative method for obtaining a preformed shape in the hydroforming die. In this case, the key point is to obtain ‘useful’ wrinkles instead of ‘bad’ wrinkles. In this paper, an investigation will be conducted on how to control the shape of the wrinkle waves and its effect on the thickness distribution after hydroforming by using finite element simulation. LS-DYNA finite element software is used in this paper. An experiment has been carried out and the results obtained from experiment and simulation are in good agreement.

Effects of Preform on Thickness Distribution of Hydroformed Y-Shaped Tube

Hydroforming processes of a Y-shaped stainless steel tube with d/t (ratio of diameter to thickness) of 183 is presented. FEM simulations were carried out for analyzing the stress states and thickness distribution in the workpieces during hydroforming of the Y-shaped tube. A two-step process with preform procedure is presented to improve the stress states in the protrusion and to avoid the severe thinning at the top of the protrusion. Through the two-step hydroforming, the wrinkling and cracking defects were all avoided and sound components were produced.

Thickness Demarcation Circle of Double-Cone Tube during Hydroforming

The analytic formula of the thickness demarcation circle during hydroforming of double-cone tube is derived by using the mechanical analysis and the total strain theory. The effect of friction coefficient, expansion coefficient, ratio of axial stress to internal pressure, length of feeding zone, and initial thickness of tube on the thickness distribution can be given by this formula quantitatively, and the analytic results were compared with the FEM analysis and experimental results. The results show that with the increasing of friction coefficient, the ratio of axial stress to internal pressure, the relative length of feeding zone, the distance between thickness demarcation circle and tube end decreased, that means the increasing of length of the thinning zone, and with the increasing of relative thickness of tube blank, the distance between thickness demarcation circle and tube end increased, that means decreasing of length of the thinning zone.

An Approach for Increasing Branch Height of a Hydroforming T-Joint With Smaller Branch Diameter

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.Copyright