# The Analysis of Key Technologies for Sustainable Machine Tools Design
## 4 Strategies and Technologies for Sustainable Design of Machine Tools
### Cooling and Lubrication Technique  
The cooling and lubrication system is an important factor for obtaining necessary levels of precision and stability as well as reducing friction in contact zones and maintaining thermal stability. Generally, machine tools with cooling and lubrication subsystems could protect the contact area and maximize tools and machine life, which benefits the economy aspect and increases the environmental burden through electrical or compressed air form. There are two main sources of heat generated by the electrical losses of motor and the friction of bearings, as well as the cutting process. In order to solve the problem, there are several methods such as minimum quantity lubrication (MQL) systems, dry-machining processes, as well as cooling of control cabinet, water cooler, cooling pumps, cooling/heating of guideways. The cooling and lubrication technique is shown in Figure 8.  
The research [101] compares the power usage of traditional cooling, MQL and high-pressure lubrication, which shows that traditional cooling consumes the greatest energy. The challenge of dry machining mainly is oriented tool life, work-piece geometrical accuracies and surface integrity, machinability of materials, and machining processes. The different cooling system designs of motor spindles have different sustainable results, due to the main spindle needed to control thermo-elastic deformations for guaranteeing accuracy and production quality of the manufactured product. [PERSON] et al., review the minimum quantity lubrication techniques for enhancing sustainable machining, involving surface roughness, tool life, and cutting temperature [102]. The study [81] carried out one technique of a cooling system with a hot gas bypass to increase energy efficiency, which  
\begin{table}
\begin{tabular}{l} Operator safety \\ and health \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 4: Sustainability benefits for modular machine tool in each life cycle phase [99; 100].  
Figure 8: The cooling and lubrication technique. (**a**) The cooling and lubrication technique; (**b**) proportion of power consumption.  
shows that it is an effective measure for optimizing cooling equipment according to cooling capacity. Additionally, dry and cryogenic machining are compared according to the capability of reducing cost and environmental burden for sustainable manufacturing [103]. The conventional cutting fluids not only are harmful for operating personnel, but also harmful to the environment and increase the manufacturing cost. However, cryogenic cooling could improve manufactured workpieces as well as machines' quality in the long use life, which benefit on corresponding environmental and economic performance. Dry machining could eliminate hazardous cutting fluids during machining operations, which benefit the environmental factor and manufacturing cost [104]. Dry machining, however, poses many challenges to the tool life, work-piece geometrical accuracies, work-piece surface integrity, machinability of materials and machining processes. Furthermore, selection strategies of lubrication are also reviewed in the reference [105] to improve the environmental and health benefit. With the development of nanotechnology, nanofluid MQL [106] is used to assist the turning process considering the criteria of surface roughness and power consumption. It also established the sustainability evaluation model under the condition of nanofluid MQL for improving the machining performance. Other fluids also have been developed to improve surface quality using little cutting fluids such as neat-oil metal working fluids [107].  
In a word, a cooling lubricant system involves a filter, container, pumps, MQL, exhaust, and cooling system contributing to energy saving, waste reduction, and pollution emission. The design optimizes a focus on basic chiller design of hot gas bypass, digital-scroll compressor, speed and inverter controlled compressor, and cold water admixing, as well as basic hydraulic system design and exhaust system design.