# The Analysis of Key Technologies for Sustainable Machine Tools Design
## 3 Dimension of Sustainable Machine Tools
### Environmental Factors
#### 3.2.1 Energy Efficiency  
Energy efficiency is the most important environmental influence due to electricity consumption. The motivation for increasing the energy efficiency of MT includes energy costs growth, consumer awareness change, considerable potential for reducing energy consumption and costs, reduction of CO\({}_{2}\) emissions, examination of life cycle costs of machinery and equipment, changes in the legal framework, etc. In the life cycle, usage has the most significant environmental impact for the general machine tool. At present, the research and innovation practice of energy efficiency of the numerical control equipment are actively carried out. The energy consumption model and the energy efficiency evaluation of MT is very important for manufacturing energy-saving research [11]. The existing research pays more attention to the energy efficiency optimization in the use stage through optimizing process parameters and conditions, and at the same time includes monitoring and management of energy efficiency, structure configuration, lightweight, energy optimization in the moving parts, etc. Because machine tools have been widely applied in industrial sectors, smaller design improvement oriented to environment could have large influences on whole sustainability performance of MT [37]. Nonetheless, engineers of MT enterprises rarely try to improve holistic design strategies from the lifecycle viewpoint [38]. The dynamic energy modeling of an MT is established in reference [39] considering multi-source resource and dynamic characteristic in the machining process. As a result, [PERSON] [40] reviewed the energy efficiency techniques of a machining process in order to provide the improvement measure both in MT and in process. ISO14955 concentrates on the environmental impact of MT, specifically the possibilities to reduce the energy consumption as the most significant environment impact. ISO/TR 14062:2002 [41] gives the overview of holistic environmental aspects integrated into the design and development process,  
Figure 2: The main objectives of machine tool (MT) structure. which could be used as guidance for machine tool design [42]. The research is paying more attention to predicting energy demand from the design angle, and energy saving strategy of green machine tools can be divided into six levels as evaluation and modeling, optimization and control technology based on software, cutting improvement, based on the hardware optimization, and the environmental design. The energy efficiency optimization could be divided into component level (physical effect), system level (kinematics, system integration), and control level (energy management, requirements optimization). The components layer is mainly internal component characteristics such as energy efficiency of the converter, the improvement of the friction coefficient, while the control and system layer are mainly to minimize energy loss interaction between components [43]. The energy consumption of the use stage is influenced by material characteristics, machining process parameters and the characteristics of the machine itself, also related to the time of processing and standby, and average power, while cutting energy consumption relies on the precise measurement of the cutting force model and machine tool unit power characteristics. Currently, further research in underway into the processing parameter optimization method of the energy consumption of MT of use process, mainly through the experiment established mathematical relationship between the material removal rate and unit energy consumption [44]. The studies concentrate on the energy transfer in the machining process, energy consumption and energy efficiency analysis and information monitoring, etc., based on the power and efficiency calculation of the main drive system.