With the development of aerospace devices with a larger size, higher load bearing capacity, and longer life, lightweight structures with high stiffness have become basic requirements in the design and manufacture of aircraft, rockets, satellites, and other aerospace products. Carbon-fiber-reinforced composites combine the advantages of a carbon-fiber-reinforced phase and polymer-matrix phase, including a light weight, high specific strength, corrosion resistance, strong designability, and other outstanding advantages, which give them a wide range of application prospects in the aerospace field, showing great potential for development. However, in the processing and manufacture of aerospace equipment, a molding process is used to form carbon-fiber-reinforced polymer (CFRP) parts as a single piece, which makes it difficult to meet the part assembly needs. Thus, a large number of cutting, drilling, trimming, and other processes are required before the actual final assembly. At present, the most commonly used processing methods for carbon-fiber-reinforced composite materials include traditional machining, ultrasonic-vibration-assisted machining, water-jet machining, electric-discharge machining, and laser processing. However, the characteristics of CFRP, such as its heterogeneity, anisotropy, and lamination structure, make it prone to processing defects such as delamination, burrs, tearing, and heat-affected zones (HAZs) during processing, which greatly affect the load-bearing performances of CFRP parts and typically make CFRP a difficult material to process.
Laser processing is a flexible and controllable manufacturing method that eliminates the problems of tool wear and mechanical stress. It is expected to become an effective means of processing CFRP with little damage and high efficiency. However, CFRP components have different thermodynamic properties, and it is easy to produce a large HAZ during laser processing. It is necessary to comprehensively consider the change in the energy absorption of the material with temperature. Otherwise, the high-quality and high-precision processing of CFRP is difficult.
At present, research on the laser processing of CFRP at home and abroad focuses on the thermal damage problem represented by HAZs and the processing quality problem represented by the slit depth and width. The common processing methods can be divided into traditional laser processing, ultrafast laser processing, and water-guided laser processing. A traditional laser relies on the thermal effect to complete the ablation, melting, and removal of materials, which usually produces a 100-μm wide HAZ (Fig. 5). An ultrafast laser has the characteristics of an ultra-short pulse width, an ultra-high instantaneous power density, and nonlinear processing, which can effectively control the HAZ and improve the processing accuracy (Fig. 6). A water-guided laser uses a water jet to homogenize the laser light field and remove the debris, which can improve the processing quality and efficiency of CFRP processing. The increase in the processing requirements in the field of aerospace strategic planning has revealed the many advantages of laser processing, including its use in drilling/cutting, surface treatment, and welding. However, the interaction mechanism between the laser and CFRP material is complex. Researchers mainly analyze the relationship between the energy transfer and temperature rise response of different components of the material during the interaction between a continuous or traditional pulsed laser and the CFRP at the macro level, or qualitatively analyze the phase of the interaction between the laser and material based on experimental phenomena (Fig. 11). The application status of carbon-fiber-reinforced composites in the aerospace field is reviewed, with a focus on CFRP laser-processing technology.
This study reviews the research progress of various CFRP processing methods, compares and analyzes their advantages and disadvantages; introduces the current research status of CFRP laser processing from the perspectives of methods, processes, and mechanisms; summarizes the application of CFRP in the aerospace field; analyzes and discusses the remaining challenges facing CFRP laser processing; and provides the corresponding prospects. Compared with other processing methods, laser processing, especially ultrafine laser processing, can achieve non-contact "cold" processing, reduce heat accumulation, improve the processing accuracy, and is expected to become an effective means to improve the quality of CFRP processing. However, the mechanism of the thermal damage produced by CFRP laser processing is still unclear, and the nonlinear, unbalanced, and heterogeneous energy transmission process during CFRP laser processing is not well understood. In order to further improve the processing quality and efficiency of CFRP laser processing, more in-depth exploration and research are required for ultrafast laser processing technology and water-guided laser processing technology. In view of the higher micro-machining requirements of aerospace CFRP components, further research is needed on the micro-mechanism of the interaction between the laser and heterogeneous CFRP materials, and new methods and new processes need to be further developed. These efforts are expected to further improve the processing quality, accuracy, and efficiency of CFRP laser processing.
