Abstract: Thermally induced accuracy degradation in green dry hobbing is addressed by elucidating the evolutionary behavior of the transient temperature field within the dry hob spindle system with consideration of time-varying tool shifting. First, synergistic cross-scale coupling among dynamically reconfigured tool positions, bearing thermoelastic deformation, and time-evolving stiffness is revealed through an integrated thermomechanical-displacement coupling analysis, with consequent multidimensional degradation mechanisms elucidated. Subsequently, a hierarchical thermal-circuit network is formulated for the dry hob spindle system based on the electro-thermal duality theory, yielding governing nonlinear coupled equation systems under concurrent transient boundary constraints and discrete multiple-source thermal excitation scenarios. Finally, by leveraging thermo-mechanical closed-loop feedback mechanisms, a transient temperature field model and a multi-scale closed-loop iterative solver are established via synchronization of multi-node thermal-circuit networks with tool shifting displacement, enabling high-precision spatiotemporal mapping of tool shifting effects and dynamic thermal response. Excellent agreement between modeled and experimental results is demonstrated across metrics including temperature rise rate, steady-state temperature, and thermal equilibrium time. The influence of bearing preload, spindle speed, and bearing spatial position on transient temperature is revealed through model application, along with the generation mechanism of gear errors induced by spindle axis misalignment and the formation mechanism of surface texture variation under time-varying tool shifting. The results provide a theoretical foundation for precision consistency control in gear manufacturing.

Key words: green dry hobbing, spindle system, thermal resistance network, transient temperature