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This paper presents a new method of combining Minimum Quantity Lubricant (MQL) with ultrasonic assistance in deep hole drilling processes for difficult-to-cut materials, using internal coolant tools. A small amount of lubricant as 90 mL/h was provided directly into the cutting zone during deep drilling under ultrasonic vibrations exerted on the tool. A comparative experimental study was implemented for two types of drilling processes: conventional drilling (CD) and ultrasonic-assisted drilling (UAD). For each set, three different methods of lubricant feeding methods were applied, including flooding, MQL, and MQL with graphene nanoparticles. A continuous drilling process using a through-hole drill bit (D = 5 mm, L = 8D) for AISI SUS 304 stainless steel was implemented to validate the effectiveness of the proposed approach. The results show that the approach proposed can overcome the bottleneck in deep drilling using MQL, providing a higher production rate, longer tool life, and better machining performance in terms of cutting forces and processing ability. Using the newly proposed method, continuous drilling can be done in critical machining conditions, which are typically recommended by the tool manufacturers. The results are promising to expand to deep hole drilling of other hard-to-cut materials. [ABSTRACT FROM AUTHOR]

This article presents a new practical approach to gain a better insight into the machinability enhancements of ultrasonic-assisted drilling (UAD) of aluminum alloys where the depth ratio is larger than 10. UAD can provide a depth as up to two times compared to that of conventional drilling (CD). The material removal rate of UAD appeared higher than that of CD by 1.5 times. The total drilling torque was considered to consist of three components: the cutting torque, the rubbing torque and the stick-slip torque. Both rubbing torque and stick-slip torque magnitude in CD were higher several times compared to the cutting torque. In contrast, such components in UAD took a small proportion of the cutting torque. Growing rate of the rubbing torque at deeper holes in UAD was slower than that in CD about 33 times. The effect of ultrasonic assistance on the reduction of chip resistance was found to be more effective at high depth ratio. The new approach gives better insight to understand the effects of ultrasonic assistance in deep drilling and would further develop to apply in similar studies. [ABSTRACT FROM AUTHOR]

Featured Application: Deep-hole drilling processes. This paper presents a new approach to developing the torque model in deep hole drilling, both for conventional and ultrasonic assisted drilling processes. The model was proposed as a sum of three components: the cutting, the chip evacuation and the stick-slip torques. Parameters of the new model were carried out by applying the regression analysis technique, with the correlation values higher than 0.999. The data were collected from 36 experimental dry drilling tests, both in conventional and ultrasonic assisted cutting conditions, with the depth-to-diameter of the drilled holes of 7.5. The major advantage of the new model compared to previous models is that the new model of chip-evacuation torque has only one coefficient, thus making it easier to evaluate and compare different deep-drilling processes. The effectiveness of ultrasonic assistance in deep hole drilling was also highlighted using the proposed model. The new model is promising to predict critical depth and torque in deep hole drilling. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the positive effects of vibration-assisted deep drilling of aluminum alloy Al-6061. The four most important evaluation criteria in drilling—machinability, workpiece temperature, torque, and material removal rate—were chosen to be investigated. Holes with a depth-to-diameter ratio of 13 were drilled by high speed steel (HSS) twist drill bits of 3 mm diameter, using both methods of conventional drilling (CD) and ultrasonic-assisted drilling (UAD). Three levels of axial force of 6 kgf, 9 kgf, and 12 kgf were kept constant for each pair of comparison experiments. It was found that workpiece temperature and torque not only changed from one drill to the other, but were also dependent on the hole depth being drilled. Comparisons were made in-pair between CD and UAD under the same axial force and at the same order of hole numbers. The result shows that the material removal rate with UAD was up to 3.5 times higher than that with CD and the average workpiece temperature and torque in UAD were reduced by 3.5 and 6 times, respectively. Moreover, tool life in UAD was observed to increase from 2.5 to 5 times, in terms of number of holes drilled, compared to that in CD. [ABSTRACT FROM AUTHOR]