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The ultrasonic-assisted drilling (UAD) process is a technology that applies ultrasonic vibrations in the feed direction of the drill to improve drilling conditions and productivity. In recent years, UAD has been the subject of extensive research due to its advantages over the conventional drilling (CD) process, these being reported as thrust force and torque reduction, burr height reduction, improvements in surface roughness, and hole accuracy. The results of the research also showed that these benefits do not necessarily equally occur for all drilling conditions but can vary with machining and ultrasonic conditions. In particular, it is found that the drill vibration amplitude is a key factor in determining UAD benefits. However, a critical difficulty is that the all-important matter of the drill vibration amplitude at the point of material engagement, the so-called "down-the-hole" amplitude, is not known due to inaccessibility. This difficulty, not faced, for example by the ultrasonic-assisted turning (UAT) process due to its visual access, has prevented measurement of load effects on UAD, as well as verification of analytical models of the process. In this study, a technique to measure the effect of load on drill vibration amplitude during UAD is presented. The technique is based on examining the surface of the drilled hole, where minute, oscillatory traces of the vibrating drill tip are found that correspond to drill tip vibrational amplitude. This data, when coupled with in-process laser vibration measurements at the drill chuck, as well as no load amplitude measurements, permit the effects of load on vibration amplitude to be determined. Results have shown that drilling loads cause measurable reductions in drill vibration amplitude and must be accounted for in UAD procedures. [ABSTRACT FROM AUTHOR]

The ultrasonic-assisted drilling (UAD) process is being developed due to its apparent advantages over the conventional drilling (CD) process in terms of thrust force and torque reduction and improvements in surface finish and hole accuracy. However, as with CD, heat generated during UAD might affect tool life, including damage to the cutting edges of the drill. The research reported here has two main objectives: (1) finding the best technique to measure temperatures in UAD, and (2) measure the effect of ultrasonic vibrations in heat generated in UAD. In this paper, two scenarios are used to examine five temperature measurement techniques, these being embedded thermocouples in the material, infrared (IR) sensor, IR camera, and embedding thermocouples in the drill cooling channels and surface thermocouples. It is found that embedding thermocouples in the drill cooling channels is the best and most reliable technique for measuring temperature in UAD. This method is then used to investigate the effects of ultrasonic vibrations on heat generated in UAD of aluminum 6061, alloy steel 4340, and stainless steel 316. The effect of ultrasonic vibrations on thrust force is also studied in this investigation. [ABSTRACT FROM AUTHOR]

The ultrasonic-assisted drilling (UAD) process is a technology which applies high frequency vibrations (>20 kHz) at amplitudes of 2-20 μm in the feed direction to the drill tip in order to improve machining conditions and productivity. Past work in this field is reviewed, noting the valuable foundation provided by laboratory-based research systems. This work is aimed at the development of a robust UAD module, fully compatible with computer numerical control (CNC) systems, and able to function in a production environment, describing results of drilling tests on 4340 steel. The UAD module, designed using FEA methods, with a 16- mm carbide drill, attached by shrink fit, is used to study the effects of ultrasonics on thrust force, torque, surface quality, hole size, and the microstructure of drilled 4340 steel. In order to provide a better understanding of the performance of this module, two different test scenarios were designed and the results for each were compared with the results obtained from baseline settings for conventional drilling. The results show that ultrasonic vibrations not only can reduce the average values of thrust force and torque but also can improve the surface quality of the hole. It is also found that a major increase in productivity could be achieved by using ultrasonic vibrations. Finally, the effects of ultrasonic vibrations on hardness and microstructure of the drilled hole is assessed and the results show that high frequency vibrations do not have significant effect on dimensional accuracy or on the microstructure of the drilled holes. [ABSTRACT FROM AUTHOR]