Thermal behavior simulation and stabilization for a mechanical spindle with external cooler across grease-coated interface

Spindles in precision boring machine often work in low speed and heavy load without internal cooling, and the thermal error is non-negligible. An external cooling system was proposed, and the effectiveness of the proposed scheme needs to be preliminarily verified by simulation before building the cooling system. Thermal simulations of the spindle with an external cooler require calculating the thermal resistance of the thermal grease-coated interface between the cooler and spindle. Models describing the contact thermal resistance and total thermal resistance for metal contact filled with silicone grease based on solid–liquid interface force equivalence were described in this paper, and experiments were also conducted to verify the accuracy of these models. The contact thermal resistances between the cast iron/copper and silicone grease on flat or cambered surfaces were calculated, and the bulk thermal resistance of the silicone grease layer was calculated. The total heat transferred between the cooler and the silicone grease-coated interface of the spindle was calculated. Heat transfer and heat generation in the spindle were calculated, and a finite element model was established to verify the effectiveness of the designed external cooling scheme. Finally, the proposed cooling scheme is developed, and quantitative analysis for experiments show that the constant temperature cooling (20 °C, 18 °C, and 16 °C) significantly improved the thermal error stability, hence decreases the time of reaching thermal equilibrium by 42.95%, 39.57%, and 39.84% under a rotation speed of 1500 rpm, and 23.94%, 51.21%, and 42.07% under a rotation speed 3000 rpm.