Hydroforming processes of metal tubes and sheets are being widely applied in manufacturing because of the increasing demand for lightweight parts in sectors such as the automobile, aerospace, and ship-building industries

A cylindrical deep drawing test was conducted for the purpose of improving the drawability, product accuracy, and quality in warm deep drawing using a superplastic material with large strain rate dependence. Then, the effects of blank holding force (BHF) and punch speed (SPD) on the flange wrinkle behavior and wall thickness distribution were investigated by experiments and theoretical analysis. A Zn-22Al-0.5Cu-0.01Mg alloy superplastic material SPZ2 with a sheet thickness of 1 mm was employed as the experimental material, and a cylindrical deep drawing experiment with the drawing ratio (DR) of 3.1 and 5 was performed at 250 °C. A good agreement was qualitatively obtained between the elementary theory on the flange wrinkle limit, the fracture limit, and the experimental results. In addition, the authors examined each variable BHF and SPD method obtained from the theory and experimentally demonstrated that the variable BHF method has a great effect on uniform wall thickness distribution and that variable SPD has a great effect on shortening the processing time for superplastic materials. Furthermore, the authors demonstrated the effectiveness of the variable BHF/SPD deep drawing method that varies both BHF and SPD simultaneously.

In this study, the material behavior in the T-shape microtube hydroforming (MTHF) of pure copper and stainless-steel SUS304 microtubes with an outer diameter of 500 µm and wall thickness of 100 µm was examined experimentally and numerically. This paper elucidates the basic deformation characteristics, the forming defects, and the forming limit as well as the effects of lubrication/friction and tube length. The hydroformability (bulge height) of the SUS304 microtube was shown to be higher than that of the copper microtube because of the high buckling resistance of SUS304. Good lubrication experimentally led to the high hydroformability of T-shape forming. The length of the microtube significantly affects its hydroformability. Friction resistance increases with increasing tube length and restricts the flow of the microtube material into the die cavity. By comparing the T-shape and cross-shape MHTF characteristics, we verified the hydroformability of the T-shape microtube to be superior to that of the cross-shape microtube theoretically and experimentally. In addition, the process window for T-shape MTHF had a narrower “success” area and wider buckling and folding regions than that for cross-shape MTHF. Furthermore, conventional finite element (FE) modeling without consideration of the grains was valid for MTHF processes owing to the many grains in the thickness direction.

This paper deals with the identification of an empirical equation for predicting free surface roughness evolution. The equation has been proposed elsewhere, and, in contrast to widely used equations, assumes that the evolution of free surface roughness is controlled by two kinematic variables, the equivalent strain, and the logarithmic strain normal to the free surface. Therefore, an experimental program is designed to account for the effect of the mode of deformation on free surface roughness evolution. Thin sheets of aluminum alloy A5052-O and pure copper C1220P-O alloys are used to conduct the experimental program. In addition, numerical simulation is performed to calculate the evolution of free surface roughness under the same conditions. Comparison of experimental and numerical results shows that the accuracy of the numerical results is good enough. Then, numerical simulation is extended to the domain in which no experimental results are available. Discrete functions so found are fitted to polynomials. As a result, continuous functions that represent the empirical equation for predicting free surface roughness evolution for A5052-O and C1220P-O alloys are determined. These equations can be used in conjunction with solutions to boundary value problems in plasticity for predicting the evolution of free surface roughness in metal forming processes.