An experimental study on the effect of thinning band on the sheet formability in negative incremental forming

In negative incremental forming, a characteristic thinning band occurs on the parts when wall angles approach the maximum obtainable [D. Young, J. Jeswiet, Wall thickness variations in single point incremental forming, Proceedings of the Institute of Mechanical Engineers, Part B, Journal of Engineering Manufacture 218 (2004) 1453–1459]. The effect of this ultra-thin band on the fracture occurrence of part was studied in the current investigation. It was found that the occurrence of a thinning band on the test specimen of a formability test does not mean an effect on the test result. A reduction in the formability due to the occurrence of the thinning band occurs only if the specimen fractures in the flange area. In order to evaluate the real forming limit of a sheet metal, a condition regarding the occurrence of part fracture is proposed.