In-process determination of fiber orientation for layer accurate laser ablation of CFRP

Complex repair geometries including stepped laser ablation of damaged areas in CFRP parts significantly increase the bonding strength of the reconstruction patch. In the optimum case the steps in the repair geometry exactly fit the fiber layers. Unfortunately, the layer thickness is subject to manufacturing related fluctuations. Therefore, the step heights have to be adapted for each layer. To meet these requirements a controlled laser ablation process using optical coherence tomography (OCT) for optical distance measurement was developed, allowing to control the ablation depth with an accuracy of <10 µm. Furthermore, the 2D-Fourier transform of the reconstructed surface topography shows that certain wavelengths only appear perpendicular to the fiber direction, which enables the determination of the fiber orientation. OCT-controlled ablation together with the determination of the fiber direction was used to demonstrate layer accurate repair geometries.