The increasing demand for work pieces made out of difficult-to-machine materials and for high performance machining parameters, as well as stricter environmental requirements, are driving the machining industry's needs for alternative cooling lubrication strategies. Cryogenic cooling is therefore an innovative approach to improve process performance and sustainability. For example, liquid carbon dioxide (LCO2) can be used as a cryogenic medium for process cooling with the option of cryogenic minimum quantity lubrication (cMQL). As part of this research, the effects of the internal supply of CO2 through the spindle on the cooling capacity and on the spindle itself are investigated in a test setup. Before the LCO2 enters the spindle, it can be stabilized in its density by adapting the CO2 pre-cooling temperature to ensure the highest possible constant cooling capacity and adaptive control of the cooling capacity through the spindle. The main tests focus on the filling and evacuation of the spindle with the cryogenic medium at the start and end of the machining process or during tool changes. In addition to the time required for filling and evacuation, the main research criteria are the monitoring of the spindle temperature at the spindle inlet and outlet. Low spindle temperature due to expansion of the LCO2 in the spindle can be avoided by flushing with gaseous CO2. The investigations of spindle temperatures and filling and evacuation times compare both a one-channel and a two-channel spindle concept, as well as the orientations of the machine tool's main spindle in a horizontal or vertical design.
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