Liquid and supercritical CO2 as cryogenic coolant for machining with internally cooled drills

Cooling and lubricating fluids are important in manufacturing for friction reduction, heat dissipation, wear protection, and chip evacuation. Conventional strategies, such as flood cooling and Minimum Quantity Lubrication (MQL), have limitations: flood cooling is expensive and ineffective in deep-hole drilling, whereas MQL offers good lubrication, but insufficient cooling. Replacing the compressed air in MQL with carbon dioxide combines efficient cooling and lubrication in cryogenic Minimum Quantity Lubrication (cMQL). While cMQL with CO 2 has been widely studied in milling and lathing, systematic drilling studies remain limited. This work evaluates the influence of the CO 2 mass flow rate and injection temperature, and the presence of lubricating oil, on drilling performance in 1.4571 stainless steel. For an 8 mm drill, a CO 2 mass flow rate between 0.3 g/s and 1.7 g/s with added lubricant yields moderate drilling forces, small segmented chips, and a minimum surface roughness of S a = 0.22 µm. • Drilling with CO 2 -based cryogenic Minimum Quantity Lubrication was studied. • Drilling experiments with liquid and supercritical CO 2 as coolant were conducted. • Carbon dioxide can provide efficient cooling in drilling applications. • Drilling with CO 2 as cryogenic coolant requires throttling it near the drill. • Suggestions are made for the design of drilling processes using CO 2 as a coolant.