Experiment analysis on defects in ultrasonic-assisted drilling of carbon fiber reinforced plastic with different diameter drills

Carbon fiber reinforced polymers (CFRP) are increasingly used in aerospace, military, and automotive applications due to their high specific strength and corrosion resistance. CFRP components usually require small-hole machining before assembly. CFRP parts are susceptible to defects such as tears and uncut fibers during hole machining. Ultrasonic-assisted drilling (UAD) contributes to the suppression of their defects. However, preliminary experiments revealed that the effect at different diameters is not the same. Therefore, this paper innovatively compares the effect of ultrasonic-assisted machining on the suppression of defects under different hole diameters and investigates the mechanism. The effects of machining parameters such as ultrasonic power, feed rate, and rotational speed on burr and tear defects of holes under different hole diameters are experimentally studied and theoretically analyzed. It was shown that the lowest defective machined holes were obtained at 50% (4 μm) ultrasonic power for all hole diameters, while higher ultrasonic power would result in an increase in machining defects. Compared with small hole diameters, there are relatively fewer uncut fibers at large hole diameters, but the tearing defects are more severe. The defect suppression effect of ultrasound is more pronounced at larger holes. The change in cutting force due to ultrasound is an important reason for the difference in machining defects. At a diameter of 6 mm, the longitudinal cutting force decreased by 58.7%, while uncut fibers and tearing defects decreased by 45.1% and 12.6%, respectively. This study can provide a theoretical basis for the selection of ultrasonic power and other parameters when machining holes of different diameters.