The main goal of energy-efficient manufacturing is to generate products with maximum value-added at minimum energy consumption. To this end, in metal cutting processes, it is necessary to reduce the specific cutting energy while, at the same time, precision requirements have to be ensured. Precision is critical in metal cutting processes because they often constitute the final stages of metalworking chains. This paper presents a method for the planning of energy-efficient machining processes based on numerical simulations. It encompasses two levels of planning flexibility: process adjustment and process design. At the process adjustment level, within the constraints of existing machines and tools, numerical simulations of orthogonal cutting are used to determine cutting parameters for increased energy efficiency. In this case, the model encompasses specific cutting energy, tool wear, chip geometry, and burr shape. These factors determine the energy and resources required for the chip formation itself, tool replacements, cleaning and deburring and with that the overall energy efficiency and precision. In the context of process design, with the ability to select machines, machine configurations, tools, and cooling systems, numerical simulations of cutting processes that incorporate machine and tool conditions are applied in the planning of energy-efficient machining. The method is demonstrated for the case of drilling processes and supported by experimental investigations that identify the main influences on energy efficiency in drilling.