Research on mechanism of chip formation in ultrasonic-assisted drilling of DD6 superalloy

DD6 nickel-based single crystal superalloy has excellent high-temperature strength and oxidation resistance, and is widely used in high-temperature fields such as aviation engines and gas turbines. Ultrasonic-assisted drilling (UAD) can significantly improve the machinability of superalloys. The chips produced during the drilling process have a significant impact on cutting forces, temperatures, machining quality, and tool wear. In this paper, the chip formation and chip-breaking mechanisms during UAD of DD6 superalloy are studied. The geometric and mechanical chip-breaking mechanisms in UAD, as well as the effects of vibration frequency and amplitude on chip morphology, were studied through theoretical and experimental methods. The research results indicate that when the processing parameters do not meet the conditions for chip breaking in segmented UAD, the chips are long, strip-shaped chips. When the processing parameters meet the conditions for chip breaking in segmented UAD, the chips are flake chips, spiral chips or short, strip-shaped chips. The effects of vibration frequency and amplitude on chip formation were investigated through drilling simulation. The results show that the greater the vibration frequency or amplitude, the smaller the chip size. The average stress in UAD is higher than that in conventional drilling (CD), and the greater the vibration frequency or amplitude, the greater the average stress. The greater the vibration frequency or amplitude, the larger the instantaneous impact on the workpiece, making chip breaking easier.