Thermal distortion in surface pretreatment of metal-polymer hybrids using continuous wave laser radiation

Due to the increasing electrification in the automotive industry, materials with a high mass-specific strength are in great demand. In this context, direct thermal joining is an innovative approach to join metals with plastics in the sense of lightweight construction. In order to increase the joint strength, a laser-based surface pretreatment is expedient. The processing with laser radiation generates an inhomogeneous temperature field in the metal, which causes thermal distortion. The deformation can significantly influence the process stability of the subsequent joining process or even prevent its successful execution. Therefore, the thermal distortion in pretreatment was analyzed in order to understand the process behavior and to guarantee excellent joining conditions. For the pretreatment of metal surfaces, infrared continuous wave laser radiation was used. In order to understand the impact of thermal distortion, the metal surface was structured varying the process parameters such as the laser power, the velocity of the laser focal spot, or the applied area energy. Additionally, the structured area size was analyzed. The deformation was analyzed comparing the shape of the metal sheets before and after the processing. Based on the investigations, strategies to reduce distortion were derived and experimentally investigated. Upon the results, it was possible to extract design recommendations for surface structuring using remote ablation cutting. One approach is an oscillating beam guidance which shows significant potential especially in the combination with a high processing velocity.