This research investigates heat generation and workpiece temperature during deep-hole drilling of cast iron under a high air pressure minimum quantity lubrication (MQL). The hole wall surface (HWS) heat flux, due to drill margin friction and high temperature chips, is of particular interest in deep-hole drilling since it potentially increases the work-piece thermal distortion. This study advances a prior drilling model to quantify the effect of higher air pressure on MQL drilling of cast iron, which is currently performed via flood cooling. Experiments and numerical analysis for drilling holes 200 mm in depth on nodular cast iron work material with a 10 mm diameter drill were conducted. Results showed that the low drill penetration rate can cause intermittent chip clogging, resulting in tremendous heat; however this phenomenon could be eliminated through high air pressure or high feed and speed. Conversely, if the drilling process is stable without chip clogging and accumulation, added high air pressure is found to have no effect on heat generation. The. heat flux though the HWS contributes over 66% of the total workpiece temperature rise when intermittent chip clogging occurs, and around 20% to 30% under stable drilling conditions regardless of the air pressure. This paper demonstrated the significance of HWS heat flux and the potential of high air pressure used in conjunction with MQL technology.
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