Tooling system for an ironing punch with adjustable diameter

High-volume sheet metal forming processes are cost-effective and efficient, but lack on-line adjustment options, so small variations in strip thickness, for example, can bring formed parts out of tolerance and cause scrap. For ironing, which is among the most tribologically severe sheet metal forming processes, on-line adjustability would greatly improve process efficiency by solving challenges related to part height variation and redundant tool wear during punch retraction from the ironed part. This paper focuses on the ironing process, presenting a novel tooling system along with an experimental campaign that demonstrates stroke-to-stroke adjustments of the ironing punch diameter up to 3.42‰ (120 μm) of the 35.09 mm initial punch diameter. Adjustability is achieved by elastically stretching the ironing punch nose before ironing and relaxing it before punch retraction from the ironed workpiece. The tool is tested by ironing deep-drawn austenitic stainless-steel cups with an initial thickness of 0.28 mm with reduction ratios between 20% and 34%, resulting in cups with up to 5 mm height difference and 40 μm wall thickness difference. When the initial punch diameter increase exceeds 2.56‰ (90 μm), punch-workpiece contact during punch retraction is avoided, eliminating redundant tool wear. Numerical simulations of the process are conducted in LS-DYNA and verified using experimental data. The simulations are used to analyse experimentally inaccessible process conditions. By adding a suitable control system, the tooling system could be used to compensate for process variations and thereby ensure consistent ironed part height while simultaneously lowering the tribological severity of the process.