Research progress and prospects of CFRP laser surface cleaning

Researchers from Materials Science at Harbin Institute of Technology, Zhengzhou Research Institute at Harbin Institute of Technology, and Key Laboratory of Microsystems and Microstructure Manufacturing at Harbin Institute of Technology, Ministry of Education, reviewed and reported on the research progress of laser surface cleaning of carbon fiber reinforced polymer composites (CFRP). The relevant paper titled 'Research progress and prospects of laser cleaning for CFRP: A review' was published in Composites Part A: Applied Science and Manufacturing.

Carbon fiber reinforced polymer composites (CFRP), as a lightweight composite material, have been widely used in the aerospace industry. At the same time, surface cleaning of CFRP has also received attention. Laser cleaning technology, as an emerging surface cleaning method, has shown broad application prospects in cleaning resins, release agents, paints, and other aspects of CFRP surfaces. This article first provides a brief overview of traditional CFRP cleaning methods, and then focuses on the research progress of laser cleaning principles and influencing parameters. Subsequently, the influence of laser cleaning on the properties of the substrate was explored. Especially, the damage characteristics and mechanisms of laser cleaning on composite material matrices have received sufficient attention. Finally, the research challenges and development trends of laser cleaning of composite materials were discussed. In summary, this review provides a reference for the research on laser cleaning of composite materials and promotes the promotion and application of laser cleaning technology in the aerospace field.

Keywords: Polymer Composite Materials (PMC); Thermal performance; Surface treatment; Heat treatment; laser cleaning

Figure 1. History of Carbon Fiber Reinforced Polymer Composites (CFRP) Applied to Airbus Aircraft

Figure 2. Schematic diagram of carbon fiber reinforced polymer composite (CFRP) and its surface pollutants

Figure 3. Laser paint removal robot LCR: (a) CO2 laser moving through the LCR robotic arm; (b) Paint burning and evaporation

Figure 4. Laser cleaning mechanism: (a1) schematic diagram of thermally induced gasification mechanism; (a2) Infrared spectrum of the decomposed gas generated; (b1) Thermal stress removal mechanism; (b2) Dynamic behavior of paint peeling based on thermal stress effect; (c1) Schematic diagram of plasma shock effect; (c2) Time evolution of laser-induced plasma; (d1) Different ablation morphologies of 1064nm and 355nm lasers; (d2) Principle of photochemical ablation of resin molecules

Figure 5. Influencing parameters of laser cleaning

Figure 6. Cleaning effect of lasers with different wavelengths on carbon fiber reinforced polymer composites (CFRP): (a) Laser cleaning of paint and polymer coatings at wavelengths λ=1064nm and 343nm; (b) Surface morphology of CFRP after laser cleaning with wavelengths of λ=10600nm and λ=532nm; The morphology of CFRP etched by laser with wavelengths of λ=355nm and λ=1064nm; (d) Laser ablation of the heat affected zone of CFRP with wavelengths of λ=1064nm and λ=532nm

Figure 7. Schematic diagram of laser material interaction under different pulse widths

Figure 8. Application of ultrafast laser in surface treatment of carbon fiber reinforced polymer composites (CFRP): (a) After picosecond laser cleaning, the silicon/carbon ratio on the CFRP surface decreases; (b) Laser induced periodic surface structure (LIPSS) induced by femtosecond laser on carbon fiber surface; (c) The LIPSS structure endows CFRP with superhydrophobic properties. Among them, LSFL and HSFL represent laser-induced periodic surface structures with low spatial frequency and high spatial frequency, respectively, distinguished by different period lengths

Figure 9. The influence of process parameters on laser cleaning of carbon fiber reinforced polymer composites (CFRP): (a) the effect of initial energy E0 on the surface morphology of CFRP; (b) The influence of velocity V on the morphology of CFRP after laser cleaning; (c) The influence of different scanning intervals on substrate temperature

Figure 10. (a) Microstructure inside carbon fiber reinforced polymer composite (CFRP) after laser cleaning; (b) Microstructure of CFRP bonding interface

Figure 11. (a) Schematic diagram of material damage based on laser thermal effect; (b) Schematic diagram of material damage based on mechanical effects

Figure 12. (a) Time evolution of temperature distribution and material removal; (b) The ablation morphology of carbon fiber reinforced polymer composites (CFRP) under different laser modes; (c) The cutting width of CFRP under different laser scanning directions; (d) Surface temperature distribution of CFRP under different laser scanning angles; (e) The size of the heat affected zone (HAZ) at different times

Figure 13. (a) Material injection caused by the recoil force induced by gasification; (b) Short cut fibers ejected under laser mechanical response; (c) Dynamic observation images of CFRP laminates processed by pulsed laser in different atmospheres

Figure 14. Schematic diagram of the application of monitoring technology in laser cleaning process

Figure 15. Application of Finite Element Method (FEM) in Laser Cleaning: (a) Modeling of Heterogeneous Materials; (b) Multi layer shell modeling; (c) Temperature and stress field calculated based on multi-layer shell model; (d) Homogeneous material modeling; (e) Local uniform material model, where the same color represents the same type of homogeneous material; (f) Laser ablation based on birth death unit technology; (g) Laser ablation based on deformable geometry technology

This article first introduces the surface pollutants of carbon fiber reinforced polymer composites (CFRP) and traditional cleaning methods. Then, the latest research progress of laser cleaning technology in the field of CFRP was summarized from the aspects of laser cleaning principle, process and performance, and laser damage mechanism. Finally, the bottlenecks and shortcomings of laser cleaning of CFRP were summarized, and the future research focus and direction of CFRP laser cleaning technology were discussed. The main content of this article is as follows:

1. Due to labor costs and environmental pressures, traditional industrial cleaning methods require new alternative processes. Laser cleaning is a clean, automated, and controllable cleaning technology that has shown great potential in the cleaning of CFRP.
The mechanism of laser cleaning CFRP includes thermal ablation, thermal stress, plasma shock, photochemistry, etc., which depends on the 
2. laser wavelength, pulse width, material properties, and also on the process parameters. At present, the coupling relationship between various mechanisms is not fully understood.

3. Laser cleaning is a process involving multiple parameters. However, the relationship between cleaning quality and process parameters still requires more detailed research and summary.

4. Laser cleaning of CFRP faces challenges of substrate overheating and surface damage. The damage to the substrate is caused by thermal and mechanical effects during the cleaning process.

5. There is an urgent need to obtain sufficient data to evaluate the impact of laser cleaning on various properties of CFRP, such as wetting, adhesion, and especially mechanical properties. In addition, the laser cleaning characteristics of new resin based composite materials have also attracted much attention.

6. With the rapid development of laser technology, it can be foreseen that the prices of high repetition rate, high-power lasers, and expensive short wavelength lasers will continue to decline. Expected to achieve efficient cleaning of large CFRP components and low-temperature cleaning of precision structures. In summary, the current research on CFRP laser cleaning has shown great industrial application prospects and provided application demonstrations for other emerging resin composite materials.

Source: Yangtze River Delta Laser Alliance