Hole-flanging of AA7075-O sheets: Conventional process versus SPIF

Abstract

Recently, the research interest in hole-flanging for small and medium-sized batches has turned from conventional press-working to SPIF due to the advantages of incremental forming, such as flexibility and cost of tools. Both technologies have been studied separately using different approaches and, therefore, most studies cannot be easily compared. The aim of this work is to provide a better understanding of the deformation process and the material formability in hole-flanging by critically comparing both forming processes. To this end, a series of experimental tests by press-working and a SPIF process in a single stage, using forming tools with same profile radii, are analysed. The material is AA7075-O sheet of 1.6-mm thickness. The deformation process is analysed by measuring circumferential and meridional strains along the flange using Digital Image Correlation techniques. The process limits are evaluated by using the traditional Limiting Forming Ratio (LFR), which defines the maximum reachable diameter of the flange related to the initial pre-cut hole performed, as well as two additional parameters based on either the flange height or the average thickness reduction. Results conclude that the LFR is not an appropriate measurement of flangeability in processes other than conventional press-working and that SPIF is the preferred process to perform hole flanges with more flexibility in shape