In the following doctoral thesis, cryogenic milling using liquid carbon dioxide (LCO2) is presented. A novel single-channel supply of pre-mixed (a) LCO2 and (b) oil – delivered as a minimum quantity lubrication (MQL) – represents a significant advancement of cryogenic-machining technology. Cooling and lubrication capability of the mixture
LCO2 + oil (MQL), which directly affects the machining conditions, have not been individually analyzed so far. Therefore, in this thesis, cooling capability of the cryogenic media was determined utilizing a controlled heat source for simulating the machining process. Lubrication capability of the cryogenic media was determined by advanced cryogenic media streamflow analysis. Results are showing that cryogenic media offers lower cooling capability than conventional oil based emulsion. This is further reflected in a higher cutting temperature, when the cryogenic media is employed. Nevertheless, the longest tool life is achieved in cryogenic machining, which indicates the importance of sufficient cooling. In addition, lubrication plays an important role; the most suitable lubrication provides nonpolar oil in the mixture of LCO2 + oil (MQL). Furthermore, the use of mixture LCO2 + oil (MQL) was found not to adversely affect the chip shapes. Moreover, due to the significantly longer tool life, cryogenic machining is more cost-effective than conventional machining. It is also a safe machining technology, since the CO2 concentration in the air near the CNC machine, does not exceed the permitted values.
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