Hydraulic pressure enhancement of the deep-drawing process to yield deeper cups

In a novel process recently developed by the present authors, high hydraulic pressure proportional to the punch force generated in the tooling augments the drawing action of the punch, provides blank holding, and lubricates the blank-tool interfaces, yielding deeper cups. This hydraulic-pressure-assisted deep-drawing technique, which enables large draw ratios, is introduced in this paper. Hydraulic pressure proportional to the punch force provides the blank-holding force, which increases from zero at the beginning to a maximum and then drops to zero at the end of drawing-somewhat similar to the critical minimum required to suppress wrinkling. This helps to minimize the frictional resistance at the flange at the initial critical stage of drawing. The hydraulic pressure is also applied on the periphery of the flange of the cup, so that the drawing is performed in a push-pull manner, enabling higher draw ratios than those achieved in the conventional deep-drawing process. The process has inherent advantages such as the automatic coordination of the punch force, the hydraulic pressure and the blank-holding force, and low friction between the blank and the tooling, as a high-pressure liquid lubricates these interfaces. This process needs only a single-action press unaided by any cushion, thereby reducing the capital investment needed. The principle of the process is explained in this paper. Results of experiments conducted using annealed aluminum blanks of thickness 1 mm to draw cups of 36 mm diameter at draw ratios of up to 3.5 are reported here. A finite-element analysis of the process has also been carried out. Measured hydraulic pressures are compared with those calculated using a simple analytical method and those from the finite-element analysis. Strain and thickness measurements taken with cups drawn by this process are also presented. (C) 1998 Elsevier Science S.A. All nights reserved.