Modulation assisted machining (MAM) superimposes a low-frequency oscillation onto the cutting process. The otherwise continuous cutting is transformed into a series of discrete, intermittent cutting events. A primary benefit of this process is to form discrete chips of small sizes and hence to improve chip evacuation. For applications in drilling the ability to control the chip size offers a direct route to improving process efficiency and stability. In this paper, the MAM process is evaluated for drilling applications via systematic experiments in drilling copper and Ti6Al4V with a two-flute twist drill and a single-flute gun drill. Based on the measurement of thrust force and examination of chip morphology, the continuous cutting and intermittent cutting regimes of MAM are determined experimentally in the normalized frequency and amplitude parameter space. The results are compared with those predicted by the kinematic model of MAM. Furthermore, the results clearly demonstrate the effect of chip morphology control on chip evacuation and process stability in drilling. The modulation conditions leading to the best performance in chip evacuation are discussed. The study shows that MAM is a promising process for enhancing the efficiency and stability in drilling difficult-to-cut materials and/or holes with high length-to-diameter ratio.

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