Classical and Roll-hemming Processes of Pre-strained Metallic Sheets

The goal of this investigation is to gather experimental data on the hemming of concave or convex edge-curved surface samples, to study the influence of geometry and pre-strain on roll-in and load, as well as to assess the validity of the numerical simulation of the process. A specific experimental set-up was designed to study classical and roll-hemming processes. The samples were pre-strained through biaxial tests to obtain a geometry and strain history similar to that of industrial parts. Flanging, pre-hemming, and hemming loads were recorded and geometrical measurements were taken after each step for the 6000 series aluminum alloy samples. It is shown that sample geometry influences both the roll-in and the load, though no clear relationship could be established. Results also show that the roll-in from roll-hemming is lower than from classical hemming and that its evolution greatly differs between the two processes. Tests on the different cases studied also indicate that classical hemming is more likely to cause damage.