Development of a mist-sensor for MQL machining and effects of pattern of jetted oil mist on drill wear

This paper deals with the effects of consistency of jetted oil?air mixture for minimum quantity lubrication (MQL) drilling. The quantity of supplied oil mist mainly affects tool wear and accuracy of the drilled hole. However, there is no method to detect such a mixture jetted from the drill tip. In this study, a "mist-sensor" as a detector for the mixture was developed by the optical dispersion principle. Practical performance of the mist-sensor was examined, and various patterns of jetted mixtures were examined in actual MQL drilling. The results obtained were as follows. (a) Oil-air mixture was visible above 15 ml/h. (b) The output signal was related to the supplied oil quantity. (c) Rotation of the main spindle stabilized the pattern of the jetted mixture. (d) Drill wear was influenced by the pattern of the mixture, and the least tool wear was achieved with a pattern of 4.2 mm3/stroke and 1 Hz.