An Experimental and Numerical Study of the Thermal Issues of a High-speed Built-in Motor Spindle

The heat generated from a built-in motor and bearings in a high-speed spindle results in a rise in temperature which causes a severe deformation of the spindle. This leads to changes in the relative position of the components of the spindle head which in turn causes machining errors and possible damage to the spindle. In this study, experiments and simulations of a spindle with a built-in motor were carried out. The results showed that the primary deformation of the cutter endpoint of the spindle was in the Z-axis direction. Experimental measurements showed that after the spindle had been running at 18,000rpm for 10min, the bushing temperature reached 33.6 degrees C and the endpoint of the spindle had been extended by 11.18m. Numerical results also revealed that the thermal deformation of the spindle in the radial direction is mainly thermal expansion without appreciable bending deformation. The simulation model was further used to analyze the effects of the cooling channel design. It showed that the single or double helical cooling channels were less effective than the original reciprocating cooling channels. This is because the reciprocating cooling channel design allowed staged partial heat dissipation of the coolant in the cooling loop.