Sustainable Machining: MQL Technique Combined with the Vortex Tube Cooling When Turning Martensitic Stainless Steel X20Cr13

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 (v(c) = 260, 290 and 320 m/min), feed rate (f = 0.3, 0.35 and 0.4 mm/rev) and depth of cut (a(p) = 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 degrees C can be achieved in regard to the inlet air temperature of 21 degrees C. Therefore, the minimum quantity lubrication technique with vortex tube cooling can be recommended for turning of martensitic stainless steel X20Cr13.

Automated summary

In order to contribute to sustainable machining, an investigation was conducted on the turning of martensitic stainless steel X20Cr13 using alternative cooling and lubrication techniques. The minimum quantity lubrication technique combined with vortex tube cooling was applied to determine the optimal cooling method. The aim was to identify the parameters that significantly affect surface roughness and tool life under the optimal cooling condition. Results indicated that only the feed rate significantly influenced surface roughness, while all three parameters (cutting speed, feed rate, and depth of cut) had a significant influence on tool life. Experimental results were compared with a mathematical model, and a new nozzle design allowed for simultaneous lubrication and cooling. The minimum quantity lubrication technique with vortex tube cooling is recommended for turning martensitic stainless steel X20Cr13.