On the use of Back-drawing Incremental Forming (BIF) to improve geometrical accuracy in sheet metal parts

Industrial interest about Incremental Sheet Forming (ISF) process is growing in the last years. Up to a few years ago, two main investigation ways were proposed, the former aimed at analysing the process mechanics, the latter at reproducing some “case study” geometries. In industrial applications, if the long cycle-time can be neglected in small batches manufacturing, geometrical accuracy represents a relevant drawback, especially when the product has to be coupled to one another. For this reason, in the opinion of the authors, the low accuracy is the most relevant defect of ISF processes today. Among the techniques already set-up to reduce inaccuracy, the use of different material supports or the use of “arbitrarily modified” tool trajectories are probably the most known. In this paper a simple approach is proposed, based on the process self capability to correct inaccuracy when different steps of Incremental Sheet Forming are carried out on both the part surfaces. In particular, it is demonstrated that a relevant increasing in accuracy is obtainable at the second repeated step, while new ones do not reduce the inaccuracy sensitively. The above approach builds a new scenario since it allows to keep the basic equipment (without any support) and does not require any further knowledge concerning the material behaviour after the punch action. These aspects are deeply discussed in the next chapters.