# The Analysis of Key Technologies for Sustainable Machine Tools Design
## 1 Introduction
### Challenges and Opportunities of Sustainable Machine Tool Design  
With the development of manufacturing systems of high complexity and high performance, there are higher requirements for the performance of machine tools, such as speed, precision [16], intelligence level, compositionality, reliability, and green degree. Meanwhile, global energy and resource consumption are gradually increasing, reflected in decreasing total non-renewable resources, the deterioration of ecological environment, and growing of carbon dioxide emissions [17]. More importantly, manufacturing consumes 37% of global energy demand [5; 18]. Machine tools as one of the indispensable tools for manufacturing products are typical high-energy, high-carbonmanufacturing systems due to the larger mass, longer life cycle with huge resources and energy consumption, and hence, environmental problems are particularly acute [19]. Therefore, the machine tool manufacturing industry must reduce non-renewable resources and energy consumption [20], and decrease environmental pollution [21], in order to alleviate the serious problem of resource constraints. In general, the key challenges of sustainable machine tools design are summarized as follows:  
* High performance;
* High energy consumption;
* High carbon manufacturing systems;
* Environmental burden;
* Waste volumes;
* Economy efficiency;
* Public health;
* Social benefits. Specifically, the design stage is one key step in the process of industrial production, which also determines product performance of most stages of the whole life cycle. In the design stage, the product performance such as positioning accuracy, stiffness [22], thermal characteristics, pulse equivalent, spindle speed, cost, environmental impact and health effects, have been determined for more than 70% of the manufacture, use, recycling and waste disposal phases [23]. Hence, sustainable machines arise at an historic moment, with the main performance including parts that are renewable, reducing more than 50% of the total weight, reducing more than 30% of the total power consumption, reducing more than 50% of waste emissions, and 100% material recycling [24]. Green machine tools have little environmental effect with high energy efficiency, low gas carbon emission and waste. Generally, electrical consumption accounts for most of the environmental burden of MT. However, sustainable machine tools not only satisfy environmental protection requirements, but also have the economic and social efficiency in order to achieve the sustainable development requirements. To achieve the sustainable change of industry, designers must present innovative strategies for new MT design for sustainability while improve productivity of existing machine tools. In short, the problems associated with the sustainability performance in the life cycle of machine tools can be summarized as follows:  
* What is sustainable design of machine tools? * How to design sustainable machine tools? * What degree of sustainability performance is there for machine tools? Designers of MT are attempting to handle the above issues by employing various design strategies, such as eco-design tools [25], energy minimum design [26], resource efficiency design [27], and carbon emission design [28]. Although some technologies have already been commercialized, especially for energy saving during the use stage of machine tools, they still need to be arranged in the design process, and also be applicable to design engineers. Figure 1 presents the key technologies of sustainable MT design. The dimension of sustainable MT involves technology, environment, economic and society, which will be achieved by some key techniques such as lightweight methods (bionic and topological approaches) [29; 30] and modular design using microsystems techniques, as well as sustainability assessment methods. Hence in this review, key technologies of sustainable design of machine tools in the early design stage are reviewed.