Thermal Modeling Challenges of High-Speed Motorized Spindles

Abstract

This paper investigates the thermal modeling challenges of high-speed motorized spindles up to 40,000 rpm. The thermal expansion and deflection of motorized spindles are critical determinants for the resulting tool center point displacement and the achievable machining accuracy of machine tools. In order to compensate, finite element and reduced physical models (digital twins) therefore require an accurate understanding of the thermal boundary conditions. In motorized spindles, heat sources are of great significance to the resulting temperature field. However, it is very difficult to accurately quantify the heat sources in motorized spindles. This is a particular challenge for high-speed applications exceeding 20,000 rpm, where commonly used boundary conditions are not validated. While the power loss of the electric motor could be quantified with reasonable accuracy, the calculation approaches for air and bearing friction proved to be inadequate. This paper introduces approaches to quantify the air and bearing friction of motorized spindles with improved accuracy for applications up to 40,000 rpm. The method was verified based on a coupled thermal/fluid-mechanical spindle simulation model. The mean absolute temperature difference between the model and the test bench was 1.5 K.