High-Quality Deep Micro-Holes with Near-Zero Taper Efficiently Processed in CFRP Using a Picosecond Fiber Laser

Carbon fiber reinforced polymer (CFRP) is extensively utilized in aerospace, transportation, and particularly in the rapidly evolving low-altitude economy sector represented by unmanned aerial vehicles and electric vertical take-off and landing aircraft. However, laser drilling of CFRP presents significant challenges, especially in processing deep micro-holes, due to pronounced thermal effects and hole taper. In this study, a picosecond fiber laser beam was directed into a spiral scanning machining head to establish a precision micro-hole machining system. A two-step machining strategy assisted by high-pressure compressed air was proposed: the first step employs full spiral scanning for efficient through-hole drilling, while the second step utilizes half spiral scanning to form near-zero taper circular holes. The through-hole generated in the first step facilitates the passage of high-pressure assist gas, effectively removing ablation debris and providing cooling to the inner wall. Circular holes with a diameter of 400 μm and an aspect ratio of 5:1 were successfully fabricated on CFRP with high efficiency. Both the hole entrance/exit and the inner wall exhibited excellent quality: the heat-affected zone width at the entrance was 8.1 μm, with a taper as low as 0.0045. The inner wall was extremely smooth, featuring an average roughness of 0.379 μm. The fibers and resin remained tightly bonded, and the material structure at the fiber ends was well preserved. The system demonstrated high processing efficiency and excellent consistency in fabricating deep micro-hole arrays, indicating strong potential for industrial applications.