Experimental observation of oil mist penetration ability in minimum quantity lubrication (MQL) spray

Minimum quantity lubrication (MQL) is an eco-friendly cooling and lubricating method that has its importance in machining sustainability. However, the behavior of the MQL droplets remains questionable. The present study is conducted to investigate the penetration performance of MQL with different combination of spray parameters and capillary sizes. An observation platform has been designed, which makes the overall penetration process controllable. The results have shown that the shortest penetration time was obtained with larger capillary size, higher air flow rate and the corresponding smaller droplet size. However, the increase of air flow rate has the optimal value when the objective is to penetrate to 1 mm deep from the entrance, whereas it has not shown the similar regulation when the droplet flowed deeper to the center due to the long transport distance has amplified the effects of multiple influence factors. The observation results were verified through simulation and cutting experiment.