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

摘要

In a novel process recently developed by the present authors, high hydraulic pressure proportional tothe punch force generated in the tooling augments the drawing action of the punch, provides blankholding, 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 increasesfrom zero at the beginning to a maximum and then drops to zero at the end of drawing-somewhatsimilar to the critical minimum required to suppress wrinkling. This helps to minimize the frictionalresistance at the flange at the initial critical stage of drawing. The hydraulic pressure is also applied onthe 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. Theprocess has inherent advantages such as the automatic coordination of the punch force, the hydraulicpressure 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 byany cushion, thereby reducing the capital investment needed. The principle of the process is explainedin this paper. Results of experiments conducted using annealed aluminum blanks of thickness 1 mm todraw cups of 36 mm diameter at draw ratios of up to 3.5 are reported here. A finite-element analysisof the process has also been carried out. Measured hydraulic pressures are compared with thosecalculated using a simple analytical method and those from the finite-element analysis. Strain andthickness measurements taken with cups drawn by this process are also presented.