Experimental Evaluation of Theoretically Ideal Drawing Dies

Abstract

On the basis of plasticity theory, Richmond et al. [l, 2, 3] have derived strip and wire drawing die profiles which require minimum work and result in minimum tensile stresses and strains during a given reduction. The fact that these ‘ideal’ dies do give a minimum tensile stress and strain suggests that they also may give least structural damage. To test this possibility, stainless steel strip and wire were drawn through dies of various contours and the structural damage was evaluated in terms of density decrements. Drawing work efficiencies and tensile properties of the drawn material also were evaluated. The drawings consisted of 50% single reductions of annealed 410 stainless steel 0.375 in. (0.952 cm) strip using nine dies, and 65% two pass reductions of annealed 305 and cold worked 416 stainless steel 0.250 in. (0.635 cm) diameter wires using five dies.

With few exceptions, the ideal dies produced less density decrement and had greater drawing work efficiencies than the other dies. These improvements were large where the die profiles differed most from the ideal profiles, but they were small for linear approximations of the ideal profiles. A convex circular arc profile (similar to rolling) gave the largest density decrement and least work efficiency for the 410 strip. For wire, the greatest decrement occurred at large angles whereas the least efficiency occurred at small angles, the optimum angle for least decrement being smaller than that for the least work. The drawn wire showed a weak correlation of increasing tensile elongation with decreasing density decrement. This small effect may indicate the existence of greater effects in fatigue properties (not tested). The zero entrance angle condition of ideal dies was found to be significant, and it is suggested that the exit should also be smooth and have a zero angle.