Mechanism and experimental verification of non-uniform pressure in viscous pressure bulge forming

The plastic deformation of the complex thin-walled components is not uniform. Applying a non-uniform load can decrease the thickness reduction and improve the thickness uniformity. In recent years, the application of non-uniform pressure to deform the sheet (such as magnetorheological pressure forming and viscous pressure forming) has attracted researchers’ attention. However, the characteristics of the non-uniform pressure have not been researched. Control of the non-uniform pressure in the forming process lacks theoretical support. In this study, the mechanism of the non-uniform pressure in the viscous pressure bulge test is investigated. The pressure-carrying medium, called viscous medium, is semi-solid and flowable. The inhomogeneous flow behavior of the medium produces non-uniform pressure when the maximum is at the bulged pole. The inhomogeneous deformation behavior of the medium produces non-uniform pressure when the minimum is at the bulged pole. The effects of flow and deformation are opposite. The non-uniform pressure function is derived, and the evolution of the pressure is presented. During forming, the viscosity of the medium increases with the pressure, so the effect of the flow behavior increases, and the pressure weight at the pole increases. Viscous pressure bulge tests are carried out to verify the theory. The gradient and evolution of the pressure can be controlled by the loading velocity and the property of the medium. The results provide theoretical guidance for the control of the pressure in viscous pressure forming, and the methodology is expected to analyze the non-uniform pressure in other flexible die forming processes.