Study on Springback Behavior in Creep Age Forming of Aluminium Sheets

Multi-step finite element simulation procedures have been developed using the commercial FE solver MSC.MARC for the study of springback in creep age forming (CAF) of aluminium sheets. A set of mechanism-based unified constitutive equation set has been implemented into MSC.MARC via the user defined subroutine, CRPLAW, to describe the interaction between precipitation hardening and creep behaviour of the AA7055 during CAF. The effects of ageing time, curvature and work-piece thickness, amount of load, loading rate on springback are studied. Some important conclusions are drawn: the longer the ageing time, the less the springback, but the influence declines with the increasing of ageing time; single curvature tool causes higher springback than double curvature tool; the amount of load and loading rate in creep age forming do not change the amount of springback significantly; for the same tool shapes, the thicker sheet has lower springback. In the end, the effect of loading patterns, the uniform pressure loading and the end clamping loading, on the spatial variation of springback are studied. The results show that the end clamping loading has a little lower springback than the uniform pressure loading.