In this paper, we propose a framework to characterize the energy consumption of machines and their subcomponents (e.g., spindle, coolant pump, controller, heater, hydraulic system in injection molding machine, motors in these components). This framework serves as a key component in describing the environmental impacts of decisions in manufacturing operations design and control, especially at the sub-cellular level. Furthermore, the proposed framework can be utilized to investigate the inter-relationship of operational decisions and environmental impacts within a manufacturing plant. The paper concludes with examples of the proposed framework for energy data collection on a CNC milling machine.