Automatically controlled laser-based welding process for repair of CFRP parts

Due to a high strength-to-weight ratio, carbon fiber-reinforced plastics (CFRPs) have become a standard in the lightweight industry, which results in the development of new machining and repairing methods. Specifically, CFRP with a thermoplastic matrix material is more attractive for many applications as a thermosetting matrix material. Thermoplastic matrix materials enable new joining processes due to their thermoformability and weldability. Currently, the repair process is mainly executed manually. In order to reduce repair costs, an automated, reliable, and fast process is needed. For the new laser-based repair process, first a scarf joint is prepared in a CFRP laminate consisting of a thermoplastic polyphenylene sulfide matrix material. To refill the scarf, a patch with the same matrix material and fiber setup as the original laminate is cut into shape and welded into the scarf area. In order to obtain a reliable and stable welding process resulting in high weld seam qualities, an automated controlled welding process is being used, which controls the laser power via the surface temperature, which is detected by a pyrometer. For the development of the welding process, the influence of the welding time and the surface temperature on the resulting weld seam quality were evaluated. For the analysis of the joining quality, overlap samples were welded and tested in order to determine the weld seam strength. In addition, cross sections were prepared and analyzed with a microscope. Finally, the measured results were correlated in order to determine a parameter set generating a high-quality weld seam.