Critical conditions in the ironing process of thin wall metal cups. 1st report Ironing test apparatus and factors affecting ironing limit.

Abstract

A new apparatus for ironing test has been made to resolve the critical conditions in the ironing process of thin wall metal cups. Ironing punch load (P) and frictional force (FP) acting on the punch surface can be directly measured. Two main components of FP, i. e. (FPd) on the ironing region and (FPf) on the region after ironing, are separated from one another by using Fpf estimated from the measured stripping load of the ironed cup. Thus, the axial stress in the cup wall at die exit can be exactly calculated. The results are as follows. (1) As the friction on the punch becomes higher, the axial stress in the cup wall becomes smaller and the welding becomes easy to occur. (2) The axial fracture stress in an ironed cup wall is larger than the critical stress of the original cup calculated by using the maximum load condition under uniaxial and plane strain states.