Laser surface treatment of carbon fiber reinforced polymer using near-infrared laser wavelength with variated process parameters

In this study, the surface pretreatment of carbon fiber reinforced polymer with near-infrared laser radiation is investigated. Several primary and computable secondary laser parameters were varied to identify their influences and interactions. The generated surface structures were examined qualitatively and quantitatively using optical and electronic microscopes. To quantify the ablation behavior, depth measurements of the exposed and covered carbon fibers were performed on cross sections. A correlation analysis was applied to determine process parameters, which have an influence on the matrix and carbon fiber ablation. With regard to the detachment and removal of the matrix, it was shown that with a pulse overlap of 50% and a single pulse energy of 195–344 μJ or a laser energy density of 3–6 J/cm2, 70%–85% of the carbon fibers could be exposed with minimal damage or ablation of carbon fibers at the same time. With 90% pulse coverage, more matrix residues remain on the surface due to the melting of polyamide particles embedded in the matrix. These retain the detached matrix on the surface. To ablate these, more laser energy is necessary, which leads to a higher fiber damage and ablation. However, a completely damage-free processing could not be realized. It is also shown that the matrix layer thickness, the local carbon fiber density, and the resulting carbon fiber topography have an influence on the local matrix removal. Furthermore, the damage caused by processing, such as fiber breaks, cratering, and others, was recorded and described.