# The Analysis of Key Technologies for Sustainable Machine Tools Design
## 5 Conclusions and Future Research Directions  
In this literature review, strategies and techniques are classified into partial design tools involving one or two sustainability aspects, and those covering three dimensions (environment, economy and society). The former is more mature and standard compared to the latter in the early design stage, due to uncertain elements of early design. Meanwhile, it takes into account whether or not the machine tools are to be designed and used. If the machine tools need to be designed or upgraded through an innovative approach, then it is the best opportunity to integrate the sustainability aspects, or else it should consider mainly the processing optimization method such as cutting parameters, tool path, and machining time after the machine tool service period. Additionally, we have examined influences on the three sustainability dimensions respectively for machine tools from the life cycle point of view. Strategies and technologies are identified from one part to components, then to product and system. The main conclusions are summarized as:  
1. The partial design strategies such as light weight and modular design to integrated sustainable design method have three sustainability dimensions.
2. The sustainability assessment method for machine tools to support decision-making in the early design stage. The two categories, however, are faced with the issue of considering three sustainable design dimensions simultaneously in different life cycle stages.
3. Most research focuses on the environmental burden especially energy efficiency, while sustainable product design underscored the importance of three sustainability dimensions under the condition of functional attributes.
4. The key techniques are categorized into light weight, modular design, and cooling and lubricant system, which have benefits in sustainable machine tool design in different life cycle stages.
5. Furthermore, sustainability assessment used by machine tools are described as LCA (Life cycle assessment), LCC (Life cycle cost) and LCSA (Life cycle social assessment), which should be used conveniently and relate to design parameter in early design stage. Currently, the research focuses on one or two factors for achieving sustainable design and manufacturing for machine tools.  
In future, machine tools manufacturers should not only consider the integrated design method for sustainability, but also evaluate sustainability performance through the whole life cycle. The development direction for sustainable machine tools techniques are shown as follows:  
Figure 9: The integration of intelligent technology and machine tools.  
1. The simulation technique contributes to design efficiency before manufacturing process, use and end-of-life.
2. With the development of new types of sensor, wireless monitoring technology will be used to monitor the state of machine tool usage including energy consumption, failure diagnosis, coolant fluids and lubricant oil, and so on.
3. The uniform standardization for the energy efficiency of machine tools should be developed based on standard components in order to make accurate judgments.
4. The network environment will provide more opportunities for collecting existing MT data used to improve the next generation or new product designs.  
Conceptualization, C.F. and S.H.; Methodology, C.F.; Software, C.F.; Validation, C.F. and S.H.; Formal Analysis, C.F.; Investigation, S.H.; Resources, C.F.; Data Curation, C.F.; Writing--Original Draft Preparation, C.F.; Writing--Review and Editing, C.F.; Visualization, C.F.; Supervision, C.F.; Project Administration, C.F.; Funding Acquisition, C.F. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 51605294.  
The authors declare no conflict of interest.