Abstract
In this study, varied cooling oil volume (VOV) control was developed for the oil coolant of a machine tool. This allows adjustment of the oil circulation flow rate in terms of the machining loads and rotational speeds of the spindle to remove the generated heat effectively from the spindle. A mathematical model of the cooling oil flow rate in terms of the rotating speed and torque of the spindle for VOV method is developed. From the thermal deformation experiments with the VOV method, the thermal deformations in both the Y-axis and Z-axis can be greatly reduced, by 70.1 % and 73.5 %, respectively, in variable rotational speed operation with a short operational period (10 minutes). Moreover, the VOV method was applied to shorten the required warm-up time of the spindle. The required warm-up time of the spindle can be shortened by 50 %, while the three axes of the spindle attain stable thermal conditions. In practical machining experiments, the machining accuracy with the VOV method can be greatly enhanced by 34 % to 62 % in comparison with the current case of constant cooling oil volume (COV). The VOV control system in the machine tool spindle can effectively reduce the thermal deformation and shorten the required warm-up time. In addition, the machining accuracy can be greatly enhanced.
Highlights
The development of the machine tool has only gradually evolved from multi-axis machines to intelligent machines, but the demand for ultra-precision in machine tools is invariable
For the spindle of the machine tool with the varied coolant volume (VOV) method, the flow rate of the cooling oil can be controlled by adjusting the frequency of the driving power of the oil pump in terms of the rotational speed and torque of the spindle
The VOV design is adopted and the flow rate of the coolant can be modulated in terms of the machining loads and rotational speeds of spindle
Summary
The development of the machine tool has only gradually evolved from multi-axis machines to intelligent machines, but the demand for ultra-precision in machine tools is invariable. In the 1990s, several studies indicated that the dynamic thermal error varies under different machining conditions and ranges from several tens of micrometers to several hundred micrometers, which is treated as major error source of the ultra-precision machine tool. The effect of the operational environmental temperature on the thermal deformation of the machine tool cannot be ignored. Tan et al [3] investigated the effect of environmental temperature on the thermal deformation of large machine tools. This study performed thermal hysteresis analysis of large machine tools and obtained that the fluctuations in lag time varied with different seasonal climates and environmental temperatures. The ultra-precision machine tool is sensitive to the environmental temperature and is usually installed in an environmental control chamber to avoid the effect of environmental temperature variations on the geometric accuracy of the machine tool. The initial and operational costs of an environmentally controlled factory are high
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