Cooling of spindle shaft for machining center using heat exchangers

The cooling method for machining center spindles commonly involves utilizing a fixed-side jacket cooling system with lubricating oil or coolant as the refrigerant. The jacket cooling on the fixed side can be optimally designed so that the coolant flows where it is desired to be cooled. It should have a closed loop cooling circuit and a temperature control unit. On the other hand, since the spindle shaft rotates, it is necessary to cool the shaft by flowing a refrigerant from the fixed part to the rotating part. Cooling of the spindle shaft is expensive because it requires a complex mechanism such as a well-balanced high-precision component and a rotating joint for cooling. In addition, this cooling technology causes a loss of torque due to fluid resistance because the coolant flows through a shaft that rotates at high speed. Such a complicated and high-loss cooling method enables high precision and high speed. However, it is necessary to consider improvement. In recent years, based on such a demand, a cooling method using a heat exchanger (HE), which does not use refrigerant for the rotating spindle shaft, has been studied. In this study, the effects of the HE and jacket cooling were confirmed with spindles for machining centers. Specifically, by mounting a heat pipe (HP) in the spindle shaft that transfers heat to the HE at high speed, it was possible to reduce the temperature inside the bearing by 5 K and suppress thermal displacement by 47 %. On the other hand, the heat removal amount calculated from the temperature difference of the coolant for jacket cooling did not change with or without HEs. In other words, it was found that the HE can reduce the heat quantity by the bearing and the temperature of the shaft without increasing the jacket cooling capacity.