# The Analysis of Key Technologies for Sustainable Machine Tools Design
## 4 Strategies and Technologies for Sustainable Design of Machine Tools
### Structure Principle  
Machine tool performance decides the quality of manufactured products and other machinery, which not only involve the properties of accuracy and surface quality, but also environmental effect and cost efficiency. Energy efficiency of machine tools on the system level is related to production systems [44]. The structure or layout of machine tools have also an important effect on sustainability through interaction between components as energy converters. Besides the selection of efficient components, what will be most relevant for the effectiveness of sustainability performance has to be considered. The tool path strategies and machine tool axes configurations are considered in machining process [94] for enhancing use efficiency of MT, which could reduce energy and material waste. Except the analysis of machining process and MT individually, the interaction between MT and manufacturing process [95] should be analyzed through simulation. The functional description of machine tools is general and independent from the design of MT, and also independent from the machining process implemented. The mapping from functions to machine components is machine tool-specific for a metal-cutting machine tool as shown in Figure 7.  
Figure 6: The solution of the lightweight design method for machine tools. Although different machine tools have different function and use circumstances, generally they have similar elements such as machine tool frames to provide fundamental structures. The production of machine tool frames need expensive engineering, testing and high-precision manufacturing, which are limited and cannot be altered after manufacturing for conventionally casted or welded structures. Currently, reconfigurable MT has been accepted due to update product with fastest speed and lowest costs. Machine tools have the characteristics of complexity, type diversity, and functional variability, while modular design could shorten the development period with the advantage of disassembly and reuse in the reconfigurable manufacturing system. Meanwhile, it benefits economic efficiency, functional and physical feasibility, upgrading outdated machine, material recycle and maintenance performance [96]. Therefore, a modular design method plays an important role in the development of sustainable products when at the end-of-life or ungraded. A modular machine tool has the benefit on updating and reusing at use-phases and the corresponding life-cycles to provide the basis for different manufacturing sector. Machine tool frames are the key structures to increase the sustainability performance of MT, in particular, and must gain more attention in the design process. Generally machine tools are static, while flexible manufacturing system could handle several production situation. Thus, there is the possibility of the over engineering issue with more hours, material and auxiliary resources, which generates a more environmental burden and cost for manufactured products. Once made, this cannot be changed. For solving the sustainability problem radically, the improvement of machine tool structure and energy efficiency must be considered in design phase by manufacturers and engineers. The modular design of MT could achieve the reconfigurable aim according to different use scenarios as well as benefit on reuse or remanufacture in the end-of life. Sometimes mechanical/electrical machine components fulfil several functions, e.g., a coolant system is used for machine cooling and for process conditioning. Then the energy consumption of this component can be assigned to different basic functions or sub functions. For example, a spindle unit of MT as one of the key components has the potentials of improving energy efficiency through an adapted electric drive train [45]. Similarly, cooling systems of MT with energy conservation are also a key technology for sustainable machine tool design [81], and also hydraulic units should consider energy-efficient strategies [80].