Ironing with Heavy Reduction

Summary

In the conventional ironing process the maximum reduction per die is limited to 30–40 per cent due to risk of fracture in the wall at the bottom. This means that often 5 or 6 reduction steps are necessary when cups of considerable heights are produced. A theoretical analysis shows that the application of very small die angles, α= 1–4 degs. , compared to conventional ironing, α = 8–15 degs. , and ensuring a larger friction along punch than die wall results in relief of the axial tension stress in the cup wall, thereby making very large reductions possible. Increasing strain hardening and decreasing prestrain results in increasing maximum reduction. Experiments were performed ironing Al cups at various reductions, die angles and different lubrication methods. With α = 3 degs. a maximum reduction of 87 per cent was obtained. Measurements of the punch and bottom loads at various reductions and die angles showed good agreement with the theory.