Energy index for evaluating machine tool energy performance: Classification, model and application

The wordwide mismatch problem between energy supply and demand is predicted to be worsen. Although developing cleaner energy sources is crucial, reducing energy consumption remains the primary approach to address the imbalance issue. As one of the major energy consumers in the industrial sector, machine tools often exhibit low energy efficiency. A comprehensive evaluation of energy efficiency of machine tools and the stimulation of energy-saving potential are crucial for the sustainable machining. In recent years, there has been an increasing focus on establishing energy-related indexes from governments, industries, and scholars. However, the problem how to classify, choose, and ultilize them in the production practices has not been addressed. Therefore, it is necessary to introduce and discuss the current energy indexes (EIs) and develop new EIs in a review. Firstly, the definition, classification, influencing factors, and development evolution of EIs are described. Secondly, an EI system of machine tools is proposed, including component partitioning, state recognition, energy monitoring, energy consumption modeling, EI selection, EI calculation, and EI application. Thirdly, a detailed description of top-down and bottom-up energy modeling methods is given. Then, key stages in full life cycle of machine tools are analyzed to guide the selection and optimization of EI. Finally, the limitations and challenges of EIs are identified from the aspects of energy models, dynamic energy performance, and novel EIs. The proposed EI system will serve as an important foundation for energy-saving productions in machine tool manufactures, distributors, and machining workshops, such as crankshaft, bearings, and ceramic parts.