On the quantification of strain distribution in drawn sheet metal products

When a flat sheet is drawn into a product, ideally, a uniform strain distribution is desired. However, non-uniformity in strain distribution is generated by the product geometry, tool-sheet contact conditions and material properties. It is difficult to predict as to when and where the non-uniformity will develop. Non-uniformity in thickness reduces the usable ductility and leads to an early failure. Since the individual effects of the above mentioned factors and their combinations are not easily quantifiable and often not deterministic, the combined consequence of these on the strain distribution is quantified by newly defined variables, “constraint factor”, and the “strain non-uniformity index”. In this paper, the effect of geometric, material and process parameters on the variation of the constraint factor and the strain non-uniformity index over the punch stroke will be demonstrated. It is found that the effects of the processing variables on material formability as assessed using the ANOVA are confirmed by the behavior of the constraint factor and strain non-uniformity index as well.