Sustainable manufacturing trends dictate the need for cleaner processes that are environmentally benign and with no adverse health effects. Cryogenic machining in recent times has emerged as such an effective and clean manufacturing process. In this field, a strong collaboration among partnering researches in the EU and US has been established. Prior research has proven that cooling effect in such sustainable machining operation is significant, while the lubrication effect is still either marginal or questionable. The nitrogen phase that is delivered to the cutting zone has a significant effect on this. The constant phase of the delivered fluid is first necessary condition to avoid the occurrence of thermal shocks. The first step in this direction for phase control is to be able to sense and accurately quantify the phase of the cryogenic fluid at the delivery. Therefore, this paper aims at presenting new experimental results on the use of a novel optical nitrogen phase sensor from the investigation of its robustness and response time. Additionally, a case study has been performed to show how the nitrogen phase affects the tribological properties of Inconel 718 alloy against a carbide tool. To examine this, experiments have been performed with a specially designed open tribometer to characterize the macroscopic friction coefficient and heat partition coefficient in the contact surface versus sliding velocity. Also, a simplified FEM model of cryogenic machining has been constructed to simulate the behavior of the machining process when delivering different phases of nitrogen. The delivered cryogenic fluid has been characterized in gas and liquid phases. It has been shown that liquid nitrogen can improve friction conditions more efficiently than gas phase nitrogen. Liquid phase has in general lower temperature and more dominant capability for heat evacuation and better lubrication properties than the gas phase, with the novel sensor being shown as capable of robustly characterizing the phase of the cryogenic fluid in the delivery itself.

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