Welding of FRP and metal - Welding of fibre-reinforced plastics onto metal using metallic inserts
Keywords: Faserverstärkter Kunststoff, FVK-Metall-Verbindung, Widerstandsschweißen, Metallische Inserts, Fiber-reinforced plastics, FRP-metal connection, Resistance Projection Welding, Metallic inserts
FRP in particular, are frequently used in this context, due to their high stiffness and strength. However, they are less suitable to transfer complex forces or when used in areas where high hardness or abrasive wear resistance is required. Hence, structures made of FRP are usually connected to metallic functional areas. The invention proposes a reliable method to weld FRP components onto other FRP components or onto metallic structures. This becomes possible by inserting metallic inserts into the composite, that serve as bridging points to enable a resistance projection welding process. They consist of a carrier plate and small scale form fitting elements mounted onto it. While the matrix resin is used to create an adhesive bond, the carrier plate creates an undercut between the insert and the composite. Hence, two bonding principles are used.
Thanks to the invention, it will be possible to weld FRP onto steel or FRP onto FRP and thus create a joint that effectively transfers forces and moments without any fiber damage. The technique does not exclude duroplastic matrices. This technologie enables a one-step process, that does not require prior drilling or surface pretreatment processes. The small scale form-fitting elements lead to a ductile and multi-step failure behavior that heralds a catastrophic total failure event. The matrix resing acts as a diffusion barrier and eliminates the risc of galvanic corrosion (in case carbon fibers are used). Bearing stress and stress concentrations are avoided, since holes and wide joining elements are not necessary.
Different designs for the metallic inserts have been investigated and tested. Among them the best performances so far have been achieved through the electrical resistance welding on metallic pins or metallic grids. The invention will be further developed in the framework of an AiF project with the support of industrial partners. A patent application has been filed in Germany. On behalf of the RWTH University, PROvendis is seeking a partner for further development in view of funding and licensing the technology.
An invention of RWTH Aachen.