Twisting analysis of ultra-thin metallic sheets

• Mechanical design of a twisting experiment.
• Investigation of twisting of metallic sheets after drawing.
• Twisting magnitude investigated for two configurations blank/tools.
• Uncertainty of the measures of twisting magnitude.
• Sensitivity of twisting magnitude to springback of the sections.

Twisting is one of the deformation mode occurring after springback and characterized by a torsion of a part around the axis aligned with its highest dimension. This phenomenon is experimentally difficult to highlight, because its occurrence has been evidenced in the case of elongated parts, when one of the part dimensions is much higher than the others, usually of the order of the meter. This leads to complex set-ups and often to scattered experimental results. The aim of this work is to investigate the influence of the blank alignment relative to the tools on twisting magnitude, in order to build a reliable database useful for finite element validation. Firstly, a dedicated device was designed to draw U-shaped rails of length 100 mm, made of ultra-thin metallic sheets, in order to deal with small-size parts. Experiments were carried out for two configurations, one with the sample aligned with the tools and another one with the sample intentionally slightly misaligned with regard to the tools. Accuracy of the measurements is analyzed and reproducibility of the intensity of twisting for both configurations is presented, as well as the relationships between springback of the sections, like opening of the U-shaped rail, and twisting. Parameters influencing the occurrence of twisting are discussed.