Pre-cooling Intensity Effects on Cooling Efficiency in Cryogenic Turning

The requirement for utilization of safe lubricants is rising in all parts of the industry due to human and environmental concerns. Therefore, complete omission or replacement of the mineral-based cutting fluids by safer ones is deemed to be very important in today’s machining operations. In the present study, the effect of pre-cooling in cryogenic machining using liquid nitrogen was compared with dry machining. Tool temperature, workpiece surface quality and tool wear were studied as the output response parameters. The results showed that the tool temperature had no sensitivity to the cutting parameters when liquid nitrogen was employed. However, in dry machining as the cutting parameters (i.e., cutting speed and feed rate) increased, the cutting temperature rose. Pre-cooling by liquid nitrogen led to reduction of the tool temperature by 73–86% compared with the dry method. Also, surface quality in terms of defective zones such as adhered materials, removed regions, and scratch marks was evaluated. It was observed that many defects were formed on the workpiece surface in dry machining, whereas it was completely defect free in cryogenic machining. Concerning the tool wear, the SEM images of tool rake face showed that the tool wear under the mechanisms of adhesion and breakage was observed in a vast area of the tool surface in dry machining, enhancing the creation of defects on the workpiece surface.