CFRP bonding pre-treatment with laser radiation of 3 μm wavelength: A robust solution for industrial applications

Due to a reduced structural weight, composite parts offer the possibility to increase the eco-efficiency of any mobility devices during their lifetime. Due to the mold-based production of composite parts, their surfaces are contaminated with release agent residues (e.g. silicones). Thus, the adhesion of the part’s surface is lowered, which prevent structural adhesive bonding of untreated parts. To enable this joining technology and guarantee a sufficient adhesion during part’s lifetime, a surface pre-treatment prior to the bonding process has to be performed. A laser treatment shows a high potential for an integration in an industrial process chain, but unfortunately, common laser sources lower this potential due to high investment costs (excimer laser) or the risk of causing material damage (lasers emitting in the range of 1 μm wavelength). To solve this challenge, laser radiation at 3 μm wavelength, which has several advantages (high absorption within epoxy resin, less thermal interaction concluding less risk to cause delaminations and the possibility to be guided through a fiber) was generated by frequency conversion of an industrial ND:YAG laser (at 1064 nm) and applied to the composite. The results show a good and sensitive treatment of the surface, resulting in high bonding strengths and providing a robust pre-treatment method.