Predictive cutting force model for a cryogenic machining process incorporating the phase transformation of Ti-6Al-4V

Titanium alloys have been attracting interest in aerospace industries because of their high strength-to-weight ratio. However, they are classified as difficult-to-machine materials due to poor tool life in machining processes. Cryogenic machining is a process that uses liquid nitrogen (LN2) as a coolant, and proposed as a method to enhance tool life in the present study. This paper presents a theoretical study to develop a predictive cutting force model for cryogenic machining of Ti-6Al-4V. A modified (in terms of cutting temperature) Johnson-Cook model that considers phase transformation, and a friction coefficient were used as input parameters for inclusion of the cryogenic cooling effect. The predictive cutting force model was validated based on an orthogonal cutting test. The predicted forces showed good agreement with the experimental data, with minimum and maximum error magnitudes of 1.9 and 17.7% for cutting force, and 0.3 and 32.8% for thrust force, respectively. Investigation of the effects of cryogenic cooling on the cutting force, micro-structure, surface integrity and burr height were conducted. The cutting force during cryogenic machining was increased compared to dry machining by a martensitic phase transformation of the work material. There was no effect of cooling condition on the surface roughness. The burr height under cryogenic conditions was decreased by 56.2 and 28.2% compared to the dry and wet conditions, respectively.

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