Forming of Stringer Sheets


The forming operation during the hydroforming process of sheet metals is performed by a pressure medium. Weight and strength optimized structures often use stringer elements to fulfill this requirement. A subsequent attachment of stringer elements to multi-curved surface structures are complex in many respects. Stringer sheets have to be manufactured precisely according to the face sheet. The positioning of the stringer to the face sheet and the control of the laser beam position along a 3D-curvature during the welding process are very sophisticated.


The main focus of this project is to adapt the process chain of linear bend splitting to sheet stringer hydroforming. The influence of the heat-affected zone to the material flow as well as the effect of the tolerances of the welded stringer to the failure modes has to be investigated. The result of this scientific work will be a method for dimensioning of the stringer parameters as well as the process control strategy.


The process will be studied with the help of finite element analysis .The material flow, the thinning, the distribution of the surface pressure in the flange area, as well as the stresses and the true strains will be considered for the dimensioning of the tool systems as well as for the process design. The methodical approach will be tested on sample geometries with stinger in the inner surface as well as in the outer face.


The process chain for the hydroforming process laser welded sheet stringers already gives sufficient results. Hence, the parameters which influence the hydroforming process, like the process parameters, the stringer height, thickness and distance as well as the influence of existing deformations due to the linear bend splitting need to be investigated.


The research project is funded by the German Research Foundation (DFG).