Investigation of surface integrity in end milling of 55NiCrMoV7 die steel under the cryogenic environments

Cryogenic assisted machining is experiencing growing popularity and acceptance as a toxic-free, eco-friendly, hazardless process producing improved structural components. This article deals with the analysis of 3D and 2D roughness profiles, surface morphology, residual stress and microhardness of 55NiCrMoV7 die steel after end milling operation under dry, wet, cryogenic CO2 and LN2 cooling environments. Among different cooling methods, the cryogenic CO2 was seen enhancing the surface topography and morphology due to the presence of minimal wear track. The result indicates the production of an insignificant amount of residual stress in the machined surface by the cooling environments at a spindle speed of 1989 rpm and feed rate of 0.02 mm/rev. The surface microhardness values were higher under cryogenic conditions compared to dry and wet conditions. Cryogenic LN2 provided the highest microhardness value among the four cooling methods.