Open Die Innovation: Manufacturing Metallic Weldable Composite Profiles for the Future of Hybrid Lightweight Design

Using hybrid lightweight structures based on fiber-reinforced plastics (FRP) is a promising approach to meeting the growing performance demands placed on structural components. However, this field faces significant challenges, primarily regarding the cost-effective production of composite materials and the development of efficient joining technologies. This presentation introduces an innovative hybrid design concept combining pultruded FRP profiles and metallic components. A key feature of the Fraunhofer IWU solution is the integration of a protruding metal tongue designed to enable conventional welding techniques, such as arc welding. This approach allows hybrid components to be seamlessly incorporated into existing manufacturing processes using established joining methods. A modular die system was developed to enable the production of hybrid profiles and allows for the construction of two distinct die variants. One die variant equipped with integrated pressure sensors was used for preliminary investigations. These tests analyzed cavity pressure during pultrusion as it relates to key process parameters, such as fiber volume content and process speed. The second patented die concept features an open-die configuration in which the two die halves are fastened together on only one side, leaving a lateral opening on the other side. This opening is sealed during processing by a continuous metal tongue that is directly bonded to the FRP. A custom sealing solution was developed for high-pressure processing of low-viscosity resins, such as epoxy. This results in a self-sealing die system with adjustable clamping forces. This ensures the formation of a bare metal profile that protrudes from the FRP base structure. Thus, the need for time-consuming post-processing steps, such as exposing the metal surface prior to joining, is eliminated. The functionality of the open die system was validated across different material combinations and process parameters. Mechanical testing, including tensile tests, was performed to evaluate the bond strength of the hybrid components. Additionally, welding trials were performed to evaluate the weldability of the exposed metal tongues. Then, tensile testing was conducted on welded specimens to determine residual joint strength.