Hydroforming of Laser Welded Sheet Stringers

The hydroforming of sheet metals belongs to deep drawing processes, where the forming capacitiy is performed by a pressure medium. This process is especially suitable for parts with a non-rotationally symmetric geometry. Light-weight structures require particularly weight optimized geometries with a possibility to attach joints or secondary shape elements. Weight and strength optimised structures often use stringer elements to fulfill this requirement. They are used in flat plates or in single curved bodies. The assembling of the sheet stringers is often costly in terms of time and money. Hence, the hydroforming process of those sheet stringers offers a new process chain for the manufacturing of complex, multi-curved hollow parts with pre-attached stiffeners. Thereby, tools and process control strategies are similar to the conventional hydroforming process of blank sheets. This paper describes the hydroforming process of laser welded sheet stringers. It gives a first outline of the potential and the limitations of the new process chain. Blank holder force and the fluid pressure are the main parameters during the hydroforming process.