Applicability of a laser pre-treatment for a robust subsequent bending of thin sheet metal

In conventional bending, locally varying residual stress states are one of the main causes for dispersion of bending angle. In this paper, a novel approach is investigated to reduce the dispersion of bending angle by modifying the residual stress state of thin sheets prior to the forming process. For this purpose, steel sheets were pre-treated with a nanosecond-pulsed fiber laser in confined ablation. The deflections were compared to sheets processed with thermal laser bending. It is revealed that the thermal mechanism dominates with respect to the deflection of the sheet because the deflection is in the same direction as that of laser-bent sheets. However, the induced deflection is smaller compared to the laser-bent ones. Moreover, it can be demonstrated that the robustness of subsequent bending operations is increased by the laser pre-treatment. The increase in robustness allows to achieve narrower tolerance windows for thin sheet metal without using cost-intensive tools and high punch forces.