Dual Cooling Jacket around Spindle Bearings with Feed-Forward Temperature Control System to Decrease Thermal Deformation

The temperature of most spindle head units in precision machine tools is controlled by forced circulation of liquid lubricant or coolant in order to minimize its thermal deformation. However, overcooled or thermally unstable coolant may cause an unacceptable temperature distribution in the spindle head unit. Accordingly we propose the incorporation of two concentric heat-exchange jackets into the spindle head unit. The inner jacket allows heat exchange with the overcooled oil, after which, oil at a constant temperature is circulated through the outer jacket so that the temperature distribution of the head unit may become uniformly moderate. As a result of this study we developed a feed-forward temperature control method to adjust the oil temperature prior to heat generation at the spindle bearings. Using a bench-lathe model and our oil temperature regulator, it has been confirmed that the dual cooling jacket structure is practically effective in decreasing the thermal deformation of the spindle as well as the machine tool itself when used in the feed-forward temperature control system.