Coolant Channel and Flow Characteristics of MQL Drill Bits: Experimental and Numerical Analyses

In minimum quantity lubrication (MQL) machining, mist flow plays a critical role in both lubrication and cooling. This paper aims to characterize the mist flow structure of different coolant channel designs for through-tool MQL drilling. Two different channel geometries (circular and triangular cross-section) and two sizes of each channel were selected for both experimental and computational analyses. The flow structure was captured by a high-speed camera and explained using computational fluid dynamics (CFD). The results showed that, for all the channel geometries, higher oil concentration was found close to the drill center. Specifically, in the triangular channel, the flow tends to accumulate at three corners. This study also measured the airspeed, which increased with the hydraulic diameter of the channel. These results have demonstrated the effects of channel geometry and the feasibility of using CFD in mist flow analysis.