Experimental and FEM analysis of dry and cryogenic turning of hardened steel 100Cr6 using CBN Wiper tools

Employing cutting fluids in machining processes, especially for difficult-to-cut materials, improves machinability through prolonged tool life, improves surface integrity and chip evacuation. However, like oil and water-based cutting fluids are hazardous to the environment and workers’ health, alternative solutions are required. Liquid Nitrogen (LN2) is a cryogenic fluid that can be an option due to its low boiling point (-197oC) and the fact it exists in the atmosphere at room conditions. Nevertheless, the feasibility of cryogenic cooling techniques in machining is not fully understood; this is why the Finite Element Method (FEM) could give an insight into the phenomena happening on the tool-chip/workpiece interface. This research aims to compare fundamental and industrial outputs when turning hardened steel 100Cr6 using Cubic Boron Nitride (CBN) inserts with wiper geometry in dry conditions and with cryogenic cooling. For this purpose, turning experimental tests were performed in both cooling conditions varying the cutting speed (150-550 m/min). Machining forces were measured during the tests, and then tool wear, microstructural damage, and residual stresses of the workpiece were characterised. A nose turning (3D) FEM model was also developed to understand the influence of cooling strategy on the outputs measured experimentally.