Evaluation of Required Diameter Adjustment of a Novel Ironing Punch Concept for Reducing Wear During Retraction

Tools for high-volume sheet metal forming processes generally sacrifice flexibility for productivity. For a tribologically severe process like ironing, this lack of flexibility makes mitigating galling during internal ironing challenging. In a novel concept of an adjustable ironing punch, the diameter of the punch can be rapidly and accurately adjusted to control the part height and decrease contact pressure during punch retraction, thereby reducing tool wear and lubrication requirements, while also making the process more flexible. The present study shows numerical analysis of the process of ironing the interior of a deep drawn cup made from steel grade 1.4301 and puts forward a method for estimating the required punch contraction to substantially reduce wear during retraction. Different punch diameters, cup wall thicknesses and reduction ratios are considered in a simplified process setup, with the effect of simplifications being explained based on selected examples. Results show that the required absolute punch contraction is positively correlated, and the strain required to reach that punch contraction is negatively correlated to the punch diameter. Both response variables were found to be positively correlated to the thickness change performed in the ironing process. Consequently, the design requirements of an adjustable ironing punch are the loosest for large diameter cups and low thickness changes.