Study on the mechanism of ultrasonic vibration drilling of unidirectional CoCrFeNiAl fiber-reinforced aluminum matrix composites

This study explores the drilling mechanisms of 7050 aluminum matrix composites reinforced with FeCoNiCrAl high-entropy alloy fibers under ultrasonic vibration drilling (UVAD). We analyze the influence of various vibration and drilling parameters on drilling force, Mises stress, fiber damage, delamination defects, and hole wall roughness. The findings indicate a positive correlation between drilling forces and parameters, with conventional drilling (CD) showing greater increases in drilling force compared to UVAD. UVAD reduces drilling force with higher vibration frequencies, showing a minimum reduction of 3.4 N, while increased amplitude leads to greater drilling forces, peaking at 19.7 N. Stress distribution at the hole exit is more uniform under UVAD than CD, with stress concentration decreasing as spindle speed increases and fluctuating with feed rate variations. The most significant stress concentration occurs at a vibration frequency of 5 kHz, and the most uniform stress distribution at an amplitude of 40 mu m. Fiber damage is significantly lower under UVAD than CD, with minimal damage at a vibration frequency of 25 kHz and an amplitude of 40 mu m. The tear factor in CD stabilizes after an initial rapid rise with increasing feed rate, while in UVAD, it correlates positively with vibration parameters, with vibration frequency having a greater impact than amplitude. Roughness is consistently lower after UVAD, with the largest roughness interval at the 45 degrees position and the smallest at 0 degrees. At 25 kHz, roughness is minimized in all directions except 45 degrees under a 60 mu m amplitude, and maximized at a 30 mu m amplitude.