Effect of LN2 and CO2 coolants in milling of 55NiCrMoV7 steel

The sustainable, cleaner and eco-friendly cryogenic coolants, namely, carbon dioxide (CO2) and liquid nitrogen (LN2) were compared with conventional wet coolant in this investigation. The performance and the influence of these coolants about cutting zone temperature (Tc), feed (Fx), normal (Fy) and thrust (Fz) forces, tool wear, chip morphology, surface morphology and roughness (Ra) in the machining of die steel were examined. The use of CO2 and LN2 caused a reduction of 50.49% and 53.97% respectively in Tc in comparison with the wet coolant. Similarly, the application of cryogens during the end milling operations reduced the tool wear, chip width and produced lower cutting forces. The Ra value obtained was in the range of 0.17 μm to 0.22 μm by CO2 cooling. Likewise, it was about 0.22 μm to 0.39 μm in LN2 cooling. The substantial improvement in surface topography and morphology was seen through the use of the cryogenic CO2 environment. Also, the 55NiCrMoV7 steel surface finish was better in cryogenic environments.