During manufacturing processes, firstly the raw materials are mined or recovered from ore. Then the raw materials are machined to obtain the qualified component. In this paper, energy consumption of manufacturing processes is calculated. During the manufacturing processes, usually several stages are needed, which are rough machining, semi-finish machining and finish machining. After each stage is finished, the components are inspected and classified into three groups: (1) those below the specification, (2) those within the specification, (3) those above the specification. For each category, the corresponding energy consumption is calculated. At last, the energy consumption of whole manufacturing processes is obtained.