Influence of Thermoelectrically Controlled Temperature of Spindle Front Bearings on the Warm-Up Time After a Spindle Stop

In various industrial sectors, including optics, automotive engineering, and information technology, there is an increasing demand for the production of components with high level of geometrical accuracy. In high-precision machining, a significant proportion of geometric inaccuracies can be attributed to thermally induced displacements of the tool center point (TCP). In particular, variations in the thermal load, such as changes in internally induced heat flux and the inherent thermal inertia of the machine tool, lead to prolonged periods required to reach thermal steady state. These delays adversely affect machining accuracy, particularly since the TCP is coupled to the condition of the motorized spindle’s front bearings, which are affected by internal heat sources and external heat sinks. To enhance the thermomechanical stability, a motorized milling spindle was equipped with a thermoelectric temperature control system, enabling precise control of the temperatures at the outer races of the front and rear bearings, as well as at the stator of the motor. This experimental setup was employed to investigate the effect of thermoelectric temperature control on the time required to reach steady state of axial tool displacement following a spindle stop. To simulate changes in the tool or workpiece, the spindle was brought to a stop from rotational speeds ranging from 10,000 to 40,000 1/min for a predetermined period. The influence of temperature control during this downtime on the subsequent time required to reach steady state was analyzed. The results show that thermoelectrical induction of heat during downtime can significantly reduce the time required to reach steady state conditions. The findings of this study demonstrate that, compared to a constant temperature, an adaptively controlled increase in temperature during downtime results in a reduction of the steady state time by a minimum of 62%.