Evaluation of adequacy of lubricants in MQL micro-drilling by a developed analytical model and experiments

Abstract

Minimum Quantity Lubrication (MQL) plays a very important role in providing effective lubrication in micromachining. The present study developed an analytical model to determine whether the given value of MQL flow rate was sufficient or deficient for different cutting conditions in a micro-drilling process. Similar study in micro-drilling is lacking in literature. The model was formulated considering the tool geometry, experimental value of chip thickness and workpiece material properties. The size effect phenomenon was also considered during the development of the model demonstrating the variation of rake angle in ploughing, transition and shearing regions of the micro-drilling process. It was observed that the required area of lubrication increased with feed from 1 to 8 μm/rev in the ploughing region and decreased in transition and shearing regimes. The size of the MQL droplets was experimentally determined to calculate the effective number of droplets impinging on the target area. Thereafter, the total effective wetting area was found out using the effective number of droplets and wetting area. Finally, the required area of lubrication and total effective wetting area were compared to determine the condition of sufficiency or deficiency. On transition from ploughing to shearing region, there was variation in the sufficiency and deficiency conditions of the given MQL flow rate at different cutting conditions of feed and spindle speed. The study clearly indicated that the condition of sufficiency of MQL flow rate could be consistently accomplished during micro-drilling under the higher cutting condition of feed and spindle speed.