Limit strains for CNC incremental stretch-expanding of aluminum sheets

Abstract

A new incremental process in which a tool deforms an aluminum blank to its circular tool-envelope surface was employed in order to measure the incremental forming limit. The forming limits were determined by the occurrence of rupture in the direction of tool travel. The limit strains for incremental forming were strongly dependent on the value of incremental tool-path-pitch Δh; the limit strains increased with decreasing Δh. Similar effects of Δh on the limit strain were also obtained under other experimental conditions. Thus, the incremental tool-path-pitch Δh had a major influence on the forming limit. Furthermore, the forming limits were controlled by the history of incremental strain, i.e., strain wave-form, strain range and number of strain cycles.