Experimental study of hole-flanging by single-stage incremental sheet forming

Recent studies show the capability of single-point incremental forming to successfully perform hole-flanging operations using multi-stage strategies. However, multi-stage strategies are time-consuming and, according to the geometrical and surface constraints of the part, the number of stages for obtaining a fully functional piece should be minimized. The aim of this work is to investigate the ability of the SPIF process to perform hole-flanges in a single stage, contributing to a better understanding of the formability of the sheet in this demanding situation. To this end, a series of experimental tests with 7075-O aluminium alloy sheets is performed. Three different tool radii are used to study the bending effect on failure. For the higher tool radius, an incipient postponed necking is observed in the wall of the flange, followed by ductile fracture; otherwise, necking is completely inhibited. The physical mechanisms controlling sheet failure during the process are analysed and discussed. Finally, the beneficial effects of the spindle speed on the thickness profile, surface roughness and forming force are also investigated.