Improving adjustable ironing punch performance using cemented carbide components

An ironing punch with adjustable diameter can control part dimensions on a stroke-to-stroke basis, increasing yield, production rate and tool life. This study investigates the effect of increased ironing die and mandrel stiffness in ironing with an adjustable punch. Cups deep drawn from 0.28 mm thick EN 1.4404 austenitic stainless steel were ironed using four tool configurations, reducing the wall thickness to 0.21 mm. In these configurations, the ironing die and the mandrel were made from either hardened tool steel or cemented carbide. When configured with only tool steel components, the punch diameter was increased by 60 µm (1.71‰) before ironing. After switching either the ironing die or the mandrel to a cemented carbide alternative, a similar cup was produced at 51 µm (1.45‰) initial diameter increase. Selecting a cemented carbide die and mandrel further reduced the diameter change to 40 µm (1.14‰). Simulations revealed that the lower required diameter change reduced the first principal stress in the punch after expansion. Enhanced mandrel stiffness resulted in lower punch diameter drop at the onset of ironing. The results suggest that using stiffer materials for the ironing die and the mandrel can prolong the life of the adjustable punch.