Deep-Drawing of Anisotropic Work-Hardening Sheet Metals Into a High-Pressure Medium

Abstract

Abstract Theoretical studies for the pressure-assisted deep-drawing operation have been conducted to determine the largest cup that could be drawn for different materials. Theoretical results for materials characterized by material constant n values and normal anisotropy R values were obtained considering the coefficient of friction μ as 0.0, 0.05, 0.1, and 0.2 values. Tensile instability is shown to be the most appropriate condition in controlling the limiting drawing ratio for the pressure process. Smooth and rough, hemispherical and conical headed punches were used to obtain practical limiting drawing ratios using different materials and different lubricants. Sheet metals used in this work were annealed 70/30 brass, mild steel, and annealed aluminum. Sheet metals were characterized by the relation effective stress σ = Aεn where A is a material constant and ε is strain. The anisotropy of the sheet metal was measured by R value for the rolling direction, 45° to the rolling direction and perpendicular to the rolling direction. A test rig, with a specially designed relief valve that controlled pressure in a range from zero up to 100 MPa and a specially designed strain gauge load cell, were constructed to carry out the experimental work. The pressure-assisted deep-drawing has been experimentally proven to be successful in obtaining higher limiting drawing ratios when deep-drawing with hemispherical and conical headed punches. Comparison between theoretical results and experimental results and the experiments of previous research workers has demonstrated the importance of taking friction into account in the theoretical analysis.