Potential of a novel integration technology for high-strength welding of metal-FRP hybrid structures with the help of welding inserts (WI)

The market for composites has continued to grow recently and according to the forecast will continue to do so in the future. Thermoplastic materials in the automotive industry compose the fastest-growing market segment. In order to use cost-effective thermoplastics for structural elements in the future, the development of efficient integration / joining technologies is necessary. Currently, there is no technology for joining of components taking into account properties and requirements of both materials (metal and FRP). Fraunhofer IWU has patented a technology with which the full-strength potential of the plastic-metal composite with FRP and welding inserts can be exploited. Welding inserts are metallic elements that interact with the plastic material and the reinforcing fibres. They are integrated into the plastic components during the FRP manufacturing process. Now, this technology will be transformed into a production-ready technology. The new technology approach is characterized by the following properties: BL By adapted structuring, a direct coupling between WI and reinforcing fibre as well as plastic matrix is produced.BL The welding inserts are located at defined positions in the plastic components. BL The welding inserts are integrated in the component or semi-finished product during plastic production (e.g. plastic injection moulding).BL It enables the use resistance spot welding, the standard joining technology in the automobile production, for the manufacturing of metal-FRP joints BL The welding inserts can be connected with the metallic joining partner by means of a conventional thermal joining process for metal (e.g. with conventional equipment for resistance spot welding). BL The joining is carried out by means of a low-energy thermal process and thus only leads to minimal damage of the plastic material. The main difference to conventional processes is that the welding inserts are already integrated into the FRP component during production. Thus, the connection properties between WIs, reinforcement fibres and plastic matrix material can be controlled during the production process by adapting production parameters (e.g. temperature, pressure in the injection moulding process). Integrating the WIs is separate from the second joining (welding) process. An adapted geometrical shape plus surface structuring of the welding inserts enhance compatibility of reinforcement fibres and plastic matrix leading to a much stronger bond. Due to a shorter welding process, the plastic material's thermal load is reduced to a minimum, thus avoiding damage in the joint area. The metal welding insert head absorbs the thermal energy better and rapidly lowers the temperature in the joint area.