An experiment investigation of temperature control performance for machine tool oil coolers with hot-gas bypass temperature control scheme and inverter temperature control scheme

Following the machine tool with demands of high-speed, high-precision machining and multi-axis, the heat generation of machine tool will lead to thermo growth of spindle, thermal error, etc. Therefore, the machine tool oil cooler has been frequently adopted for thermal management of heat generation for machine tool. However, it will be quite challenging to develop high-precision machining without suitable temperature control scheme. And, the machine tool oil cooler with on-off control is difficult to control the oil temperature accurately. Therefore, in this paper, the machine tool oil cooler with hot-gas bypass temperature control scheme and inverter temperature control scheme based on the PID control logic have been proposed to solve the oil temperature control problem for machine tool oil cooler. Furthermore, the temperature control performance (i.e. thermo growth of spindle, oil temperature control accuracy, and EER) of hot-gas bypass temperature control scheme and inverter temperature control scheme has been compared by means of experiment. The experimental results shows that the inlet oil temperature control accuracy can be maintained ±0.2 °C during spindle operation by using the hot-gas bypass temperature control scheme (HGB cooler) and inverter temperature control scheme (INV cooler). Furthermore, the thermo growth of spindle of HGB cooler is about 14 % smaller than the INV cooler because of hot-gas bypass temperature control scheme with thermal compensation function. However, the total power consumption of HGB cooler is about 0.18 kW higher than the INV cooler. Hence, the energy efficiency ratio (EER) of INV cooler reveals about 10.9 % higher than the HGB cooler at steady state. Furthermore, when oil flow rate declined to about half, the temperature difference between initial and final steady state temperature of the spindle is increased around 94.3 %, and the thermo growth of spindle is increased 58.7 %.