Improving the Thermal Behavior of High-Speed Spindles Through the Use of an Active Controlled Heat Pipe System

The thermo-elastic behavior of high-speed spindles has a significant influence on the machine accuracy. The Tool Center Point (TCP) changes continuously, not only due to the different temperature levels and energy inputs during warm-up, full-load and part-load operation, but also during interruptions for workpiece or tool changes. In this paper a heat pipe based tempering system is presented to control the spindle temperature and thus to keep the TCP displacement at a constant level, regardless of speed and load. As effective passive heat transfer components, heat pipes can be used not only to cool the system but also to insert heat into it. This capability of reversing the heat flow enables a high controllability of the temperature field in a bidirectional way and allows innovative capabilities of using advanced control algorithms. This paper describes the overall heat pipe concept and focuses on its potential as a key element for dynamic temperature control systems. Experimental results prove the feasibility of the concept with a simple on-off controller, achieving the reduction of the TCP displacement variation of a 2.2 kW spindle by 62% of its original value. The potential of the tempering concept forms the base for the deployment of various advanced control systems, such as Model-based Predictive Control (MPC), Fuzzy or Reinforcement Learning.