Effects of process parameters and drill point geometry in deep drilling of SAE 4144M under MQL

Deep drilling is a difficult machining operation, it often presents problems related to chip evacuation and efficiently cooling and lubrication of the cutting zone. Minimum quantity of lubrication (MQL) is an ecological alternative to wet machining. It provides better lubrication, however, it has low cooling effect and the chips are not removed away from the cutting zone by coolant. In this paper a combination of cutting speed, feed-rate and tool geometry is determined to produce smaller chips and lower workpiece temperature for deep drilling of SAE 4144 M steel under MQL lubrication condition. Full factorial design of experiment was used to plan the set of the experiments. Tool wear behavior and cross sections of the drilled holes were compared to a pressurized oil condition. Split point geometry, lower cutting speed and higher feed-rate resulted in the best chip shape and relatively low workpiece temperature in deep drilling of SAE 4144 M with MQL. The worn drill presented microchipping, adhered workpiece material on the rake face and exposed substrate resulted from abrasion of TiNAl coating. MQL resulted in longer tool life and more surface defects compared with the pressurized oil condition.