The effects of CryoMQL conditions on tool wear and surface integrity in hard turning of AISI 52100 bearing steel

This study investigates the performance of a new CryoMQL technique in the hard turning of AISI 52100 bearing steel with the conventional and wiper CBN inserts. It includes simultaneous application of indirect cryogenic cooling (CO2 and LN2) and direct minimum quantity lubrication (MQL) during machining. The CryoMQL conditions (MQL + CO2 and MQL + LN2) were compared to dry, conventional cutting fluid (CCF), and minimum quantity lubrication (MQL) conditions. The tests were performed at a cutting speed (200 m/min), feed (0.1 mm/rev) and depth of cut (0.1 mm). Tool wear, surface roughness and residual stresses (axial and hoop) were considered as the performance criteria. Experimental results showed that MQL + CO2 significantly reduced tool wear of both conventional and wiper inserts generally. Lower roughness values (Ra< 0.12 mu m) were obtained with the wiper inserts whereas the conventional inserts produced rougher work surfaces (Ra> 0.26 mu m) under all cutting conditions. Finally, it was found that the residual stresses were significantly affected by cooling/lubrication conditions and tool geometry.