7. Ultrasonic-assisted deep-hole drilling

Abstract

Drilling is one of the most common subtractive processes to make holes. In deep drilling, when the hole depth is larger than two times the diameter, the drilling torque increases exponentially. The most accepted explanation is that, as the depth increases, the increased amount of chips filled up the flutes, leading to chip clogging and thus causing the total torque increase. Several undesirable effects could be occurred due to excessive torque, such as chipping of the drill lips, thermal softening of the tool, or torsional failure of the drill. It is difficult and inefficient to take out the broken part of the tool from the workpiece. Such issues are critical problems for the smart machining processes and become a blockage in production lines. Specialized tools and techniques to improve chip evacuation in deep drilling have been developed, such as single-lip gun, tube drills, grooved tool bits, or peck drilling. Ultrasonic-assisted drilling (UAD) is a new technique providing an alternate and promising solution. This chapter presents how effective this technique can provide for deep hole drilling. Experimental data revealed that ultrasonic vibration can significantly reduce not only the cutting torque, but also the chip evacuation torque. A new and useful tool to analyze and evaluate the effectiveness of UAD is provided via a new model of the drilling torque, which consists of three components. Steps of design and realization of an UAD are also summarized with the hope of helping readers to apply in practical applications