Proceedings Article | 2 December 2020
Proc. SPIE. 11717, 24th National Laser Conference & Fifteenth National Conference on Laser Technology and Optoelectronics
In traditional air laser processing of CFRP (cutting), defects such as excessive heat-affected zone(HAZ), fiber extraction, material delamination, and fiber end expansion could occur near the incision. We proposed nanosecond water-assisted laser processing technology and conducted CFRP process research.CFRP has the characteristics of high specific strength, high specific rigidity, light weight and anisotropy. These characteristics make the machining of high-quality CFRP cuts very demanding on parameters, but traditional machining methods always make CFRP defects. The test sample was a CFRP sheet with a thickness of 3mm, which required smooth and even incisions. The test method was to conduct comparative experiments of nanosecond laser grooving in the air and water respectively to test the manufacturing efficiency, the surface roughness of the incision, and the HAZ of inner wall, we also discussed the formation mechanism of notch defects. In comparative experiments, it was found that the quality of the incision was related to the heat accumulation/dissipation ratio. This was related to the single pulse energy, pulse width, and thermal conductivity of the material. In the cut area of CFRP processed in the air, there were phenomena such as thick HAZ, scattered fibers, and slagging. The convective heat transfer of water removes a lot of heat, which significantly reduced the accumulated heat. In general, the water-assisted laser processing could make better cuts. However, it is found that there were some pits near the surface of incisions, which may be caused by the cavitation of tiny bubbles. The shock wave generated by the bubble explosion would not only destroy the fiber structure and increase the residual stress, making the radiation energy distribution uneven, but also brought damages to surrounding materials. We conduct single factor variable experiment at different single pulse energy, overlap rate, and water flow velocity. It is found that under the same frequency, overlap rate and water flow speed, as the energy of a single pulse increased, the HAZ of the material became larger. At a fixed frequency, single pulse energy and water flow velocity, as the moving speed of plate increased, the ablation threshold of the material also increased. It is speculated that it was caused by the scattering effect of small bubbles. The bubbles in the previous pulse could affect the ablation of the next pulse. In the case of small single pulse energy, low overlap rate and high water flow velocity, the influence of bubbles was weakened, and the bubbles in the previous pulse hardly affected the next pulse. Under the conditions of large pulse energy and high overlap rate, there were many large-sized bubbles and the quality of the cut was poor. Under large single pulse energy, high moving speed and high water speed, the cutting quality was the highest and the processing efficiency was high.
