Z.-R. Wang's research while affiliated with Harbin Institute of Technology and other places

Usually, flexible die forming technology and conventional stamping technology have their own separate and limited application range, as well as their own particular shortcomings. So a more advanced forming method is needed to meet the requirements of increasing component complexity. Viscous pressure forming (VPF), which uses a semi-solid viscous material as the pressure-carrying medium, is suitable for forming parts requiring large sheet deformation using a sequential forming method. In this paper, a sheet metal bulging experiment with three kinds of pressure-carrying media, viscous medium, polyurethane and steel, was studied. The results show that the specimens formed with VPF, compared with those formed with polyurethane and steel, have less wall-thinning and consequently a more uniform wall thickness distribution, and the shape of part is closer to the desired hemisphere. When bulged with back-pressure, the formability of sheet metal can be improved significantly. Thus VPF is a promising sheet metal forming method.

Viscous pressure forming (VPF), a recently developed flexible-die forming process that is suitable for difficult-to-form material, can obtain the better stress states of sheet blank during forming process in manufacturing complex shape parts. The process of manufacturing aluminum alloy ladder parts with VPF and solid metal punch was simulated by the FE software DEFORM. Under different blank holder pressure (BHP), the stress state, the strain state, the forming of small radius curved face and the distribution of thickness were analyzed. The simulation results show that, compared with solid metal punch forming, the sheet blank can flow into die cavity more easily with VPF due to the improvement of the stress states; the severe thickness reduction can be avoided, the sheet blank can contact the die perfectly and the parts have high dimensional accuracy.

The process parameters of aluminum alloy ladder bowl with viscous pressure forming and solid metal punch forming were numerically simulated by commercial finite element software DEFORM. The influence of bland holder pressure (BHP) on the formability of sheet metal was investigated. It was found that lower BHP does benefit to the distribution of thickness both with VPF and with solid punch forming. The forming force needed in VPF is bigger than that of with solid punch forming at the same stroke. The distribution of thickness with VPF is more uniform than that of with solid punch forming. Compared with solid punch forming, the damage values of work piece at the top convex corner are lower by VPF. It was also shown that fracture tendency should be reduced with VPF, so that means the formability is improved. At the same time, aluminum alloy ladder bowl was manufactured with VPF. The results show that the simulation results are in agreement with the experimental data very well.

Viscous pressure forming(VPF) is suitable for forming difficult-to-form sheet metal parts. An investigation in the effect of blank holder pressure(BHP) on VPF aluminum alloy ladder parts was conducted. Based on experimental and numerical simulation results of the effect of BHP on dimensional accuracy, Wall-thickness reduction, forming pressure, material flow and defects(such as wrinkling and fracture) of specimens, the effect patterns of BHP load path on VPF ladder parts were explained. The limits of BHP corresponding to specimens with no defect and with wrinkling or fracture defect were determined. In the limits of formable BHP, the variable load path of BHP was beneficial to drawing blank into the die and decreasing wall-thickness reduction of specimens. The experimental result show that the ladder parts of good surface fineness and high dimensional accuracy can be obtained by variable load paths of BHP.