Environmental temperature changes are a major factor in machining accuracy degradation in machine tools. As maintaining a constant environmental temperature is costly, reducing thermal deformation through machine design is important. For this purpose, it is essential to clarify the mechanisms of thermal deformation caused by environmental temperature variations. In recent years, machine tools have increasingly been required to incorporate covers for chip and coolant management as well as compliance with safety regulations. However, covers influence the heat transfer between the machine and the environment and complicate the mechanism of thermal deformation. In this study, the influence of covers on the heat transfer and thermal displacement of a turning center was investigated. The relationship between thermal displacement and temperature variations in the ambient air and machine structure was examined for different cover configurations under environmental temperature variations. Experimental results demonstrated that, while the influence of environmental temperature changes was suppressed by the machine outer cover, the temperature difference of the air within the machine outer cover increased due to the mechanical configuration, resulting in thermal deformation. Additional covers suppressed the temperature rise of the air around the structure and the structure itself, but the temperature distribution of the air and the structure was not improved, and thermal deformation was not reduced. Simulation results showed that the heat transfer rate from the air to the structure was reduced by 20% with additional covers. These results indicate that thermally robust machine tools under environmental temperature changes can be developed by appropriately designing the arrangement of covers.

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