There are several heat sources that would influence the performance of machine tool. Three main thermal displacement sources are spindle, structure, and the motors of axial drives. Among these sources, displacement in spindle system is the most critical issue to be concerned. In this article, we will share three spindle compensation methods which enable stable machine processing.

Spindle Thermal Displacement Compensation-Thermal Sensor Compensation

PT100 temperature sensors are installed to detect the variation of temperature at the spindle nose and the actual spindle growth. With these input data,  the offset which caused by thermal displacement can be compensated through a thermal compensation model.

TAKUMI had developed a function of thermal compensation on spindle and applied to our verticle machining centers, high speed bridge type machining centers and 5-axis machining centers. The test was performed on a high speed bridge type machining center H12E. The result shows a tramendous difference without compensation and with thermal sensor compensation.

+ Machine: TAKUMI H12E
+ Control: FANUC 
+ Spindle: Built-in spindle at 20000RPM (PT100 thermal sensors are installed)

The maximum spindle thermal displacement is 80μm without machine warm- up and without any compensation. 

On the other hand, we established thermal error models to predict thermal errors by reading the PT100 temperatures of the critical points in real time. The PLC was able to compensate the thermal deviation by the detection of the sensors. Even if the external environmental temperature flactuate, after running 2 hours without machine warm-up, the results show a maximum spindle thermal deviation of only 25um. The displacement has greatly improved 68%.

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