A current trend towards sustainable machining can be found in the gradual substitution of lubricants by cryogenic media in the form of liquid carbon dioxide. This strategy has been proven to reduce the tool wear and increase productivity and energy efficiency in milling processes of titanium alloys. While various adjustments to the CO2 supply system such as pre-cooling or pressurization are viable, it remains challenging to adjust the cryogenic cooling capacity to the specific requirements of each process. To do so, an approach to quantify this cooling effect by temperature measurements with functional coatings of the cutting insert during turning processes of polypropylene is proposed in this research. The results show that the influence of the nozzle distance to the cutting tool and the nozzle diameter are reduced by a variation of the CO2 density. The lowest cutting temperatures are achieved with an increase in pressure levels and hence a drastic increase in CO2 flow rates. Furthermore, the liquid CO2 based cutting temperatures are compared to those obtained by cooling with a vortex tube. The utilization of vortex tubes as a cooling strategy shows potential as an alternative for easy-to-cut materials like polypropylene, since the effort for the machine integration as well as operator safety precautions are minimized.
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