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Amongst different methods of cooling in machining, application of air is considered to be the cleanest and most environmentally friendly one. The aim of this paper was to explore the possibility of chilled air-cooling considering the corrosion resistance when turning martensitic stainless steel X20Cr13. Thus, a comparison between an alternative cooling technique where compressed air is refrigerated and jetted to the cutting zone by means of Ranque-Hilsch counter-flow vortex tube and the conventional flood cooling with oil-in-water emulsion was done. The corrosion resistance was determined by electrochemical testing and the surface condition was analysed with both Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). From the results presented herein, it can be concluded that the specimen cooled with chilled air has better resistance to corrosion activity after a certain longer time in relation to the specimen cooled with emulsion. In addition, the specimen cooled with chilled air has lower surface roughness, which has a positive effect on the corrosion resistance. Hence, in the scope of environmentally friendly machining the vortex tube based chilled air-cooling can be successfully applied when turning difficult-to-cut martensitic stainless steel. Procedia Engineering, Vol. 132, 413-418, doi: 10.1016/j.proeng.2015.12. 513. [5] Boswell, B. (2008. Use of air-cooling and its effectiveness in dry machining processes, PhD thesis, Curtin University, Australia. Vol. 47, No. 3-4, 635-645, doi: 10.1016/ j.ijmachtools.2006 Liu, N.-M., Chiang, K.-T., Hung, C.-M. (2013). Modeling and analyzing the effects of air-cooled turning on the machinability of Ti-6Al-4V titanium alloy using the cold air gun coolant system,

The development of ecological awareness followed by stringent laws on the protection of natural resources and workers direct the manufacturing industry at the development and implementation of alternative methods for cooling and/or lubrication in the machining of metals. The paper investigates the feasibility of using a vortex tube for cooling when turning martensitic stainless steel. Experimental research was conducted to understand the effects of vortex tube cooling on the corrosion resistance of the machined surface and on production costs. It has been determined that the vortex tube cooling has no significant influence on the corrosion resistance and that the tool costs have the most significant influence on the unit production cost. In conclusion, compared to the conventional emulsion cooling in metal cutting, the vortex tube cooling offers a cost-effective solution to the sustainable turning of martensitic stainless steel.

For the purpose of contributing to sustainable machining, the aim was to investigate the turning of martensitic stainless steel X20Cr13 under alternative cooling and lubrication techniques. The minimum quantity lubrication technique in combination with the vortex tube cooling, as the determined optimal cooling method using the Taguchi-based entropy weighted grey relational analysis (compared to emulsion and minimum quantity lubrication technique) in previous research when turning martensitic stainless steel X20Cr13, were applied in this research in accordance with the Box–Behnken design. The aim is to investigate, when applying the optimal cooling condition (minimum quantity lubrication + vortex) with the Box–Behnken design, which parameters have a significant influence on reducing the surface roughness parameters Ra and Rz and also on the tool life (T). The cutting speed (vc = 260, 290 and 320 m/min), feed rate (f = 0.3, 0.35 and 0.4 mm/rev) and depth of cut (ap = 1, 1.5 and 2 mm) were selected as cutting parameters. An exponential model for Ra, Rz and T was obtained. According to the ANOVA results, it can be seen that only the feed rate had a significant influence on Ra and Rz. For tool life, according to the ANOVA results, it can be seen that all three parameters (cutting speed, feed rate and depth of cut) have significant influence on the tool life (T). Experimental results were compared with the results of the exponential mathematical model and presented in diagrams. A new nozzle was designed for this research to allow micro-droplets from the MQL unit and chilled compressed air from the vortex tube to be connected in one stream (single-channel system) before entering the cutting zone, thus allowing for simultaneous lubrication and cooling. For the used vortex tube system with an air flow of 708 L/min and the inlet air pressure of 0.69 MPa, a temperature drop of −29 °C can be achieved in regard to the inlet air temperature of 21 °C. Therefore, the minimum quantity lubrication technique with vortex tube cooling can be recommended for turning of martensitic stainless steel X20Cr13.

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