Transient Thermal Behavior of the Worktable Spindle System in Dry Hobbing Machine Tool based on Thermal Network Method under Time-Varying Loads

To address the issue of thermally induced accuracy degradation in dry hobbing machine tool during processing, this study investigates the transient thermal behavior (temperature rise and thermal deformation) of the worktable spindle system under the interaction between thermal and force loads using the thermal network method. First, the fluctuation pattern of bearing force loads on the worktable spindle system under the axial feed motion of the hob is systematically analyzed. The influence mechanism of force load fluctuations on the variation of thermal loads in the spindle system is explored, and the temperature rise characteristics of the worktable spindle system are subsequently revealed. Then, based on the spatial geometric structure of the system, a hierarchical heat transfer block diagram model and its corresponding computational model are established using the thermal network method. Finally, an analytical model for the transient temperature of the worktable spindle system is developed based on the principle of energy conservation. A closed-loop iterative solution method is proposed for this analytical model, incorporating the viscosity–temperature characteristics of bearing grease and contact mechanics. The interaction mechanism between thermal and force loads on the worktable spindle system is analyzed by alternately updating the heat source terms and bearing force loads. Experimental verification shows that the deviation between the average temperature rise calculated by the analytical model and the measured value is less than 5%, and the deviation in thermal equilibrium temperature is less than 2%. The deviation between the calculated radial thermal deformation and the measured value is less than 7.5 μm. These results confirm the validity and reliability of the proposed analytical model. Further quantitative analysis reveals the influence of grease viscosity degradation, spindle speed fluctuation, and bearing preload mismatch on the transient thermal behavior of the worktable spindle system under thermal–force load interaction. This study provides support for thermally induced precision control of dry hobbing machine tool.