Stamping of stringer sheets

Abstract

Light-weight performance of load carrying structures can be increased through the use of bifurcations. Stringer sheets make use of this design principle. They consist of a base sheet with stiffening ribs or stringers. In this work the stringers are attached to the flat base sheet via laser welding and afterwards the part receives its targeted 3D shape in a subsequent forming process. While a larger height of the stringers is advantageous in terms of light-weight performance, it can lead to higher compressive stresses in concave areas of the part, causing buckling of the stringers. Previous studies made use of hydroforming for the manufacture of the 3D shaped stringer sheets. During hydroforming a side support to the stringers is given by the pressurized medium. Due to relatively long cycle times, it is not suitable for highly efficient mass production. Hydroforming also has shortcomings in the attainable geometries. This paper presents a new industrial-suited stringer sheet stamping process which is up to 20 times faster than current stringer sheet forming processes based on hydroforming. Furthermore, a numerical model allowing the prediction of stringer buckling is provided. Both, process and numerical model, are experimentally validated.