A novel hydraulic-pressure augmented deep-drawing process for high draw ratios

Recently, a new hydraulic-pressure assisted deep-drawing process was invented by the author, this new method having evolved from a hydraulic device for deep-drawing with the blank-holder force approximately proportional to the punch force, developed successfully earlier. The present method also generates a hydraulic pressure proportional to the punch force, although the present hydraulic pressure, is greater. The blank-holding force in the present case is also dependent on the hydraulic pressure, but it does not vary in a simple manner. In addition, the present process uses the hydraulic pressure to push the periphery of the flange of the cup being drawn radially inwards in this way the hydraulic pressure augmenting the punch force and making it possible to achieve greater draw ratios than those possible in the simple deep-drawing process. Since the hydraulic pressure depends on the punch force, both the punch force and the pressure are automatically coordinated, thereby eliminating the need for any control system to coordinate them. The present process also provides the blank-holding force automatically, requiring only a single-action press. Tooling was designed and constructed for drawing 36 mm diameter cups at draw ratios of about 3.0 with the present method. Tests conducted with annealed aluminium blanks of thickness 1 mm were successful at a draw ratio of 3.11, the latter draw ratio being limited by the present tooling. With the full potential of the process utilized and new tooling constructed to accommodate larger diameter blanks, greater draw ratios may be achieved. This paper presents the underlying principle of the process, the design and development of the tooling and the experimental results obtained in the use of the tooling.