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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]