# Sustainability-Based Analysis of Conventional to High-Speed Machining of Al 6061-T6 Alloy
## 1 Introduction  
Sustainability in manufacturing is the creation of products through processes that have minimum environmental impact, are economically viable, and pose no threats to workers [1]. From the viewpoint of machining processes, sustainability largely depends upon machining parameters, workpiece materials, and lubrication techniques [2]. The selection of machining parameters plays a significant role in the efficient utilization of cutting tools and machine tools during a machining operation. The significance of cutting parameters becomes more pivotal when machining is performed on CNC machines, which usually involve high initial and operating costs. An important component of the operational cost of CNC machines is energy cost, which has a substantial share (around 17%) in the total cost of a production machine tool [3]. This cost of energy consumption is expected to grow further in coming years due to an increase in fuel prices. In addition to the financialburden, the environmental aspect of machining processes is also of great concern [4]. Studies suggest that electrical energy consumption during a machining process is the single largest source of environmental burden [5]. Therefore, reduction in electrical energy consumption is highly relevant from the viewpoint of enhancing the sustainability of machining operations. The electrical energy supplied to a machine tool is partly consumed in operating its main components (spindle, hydraulic system, etc.) and partly consumed in the actual machining process [6], as shown in Figure 1. Therefore, the optimal use of electrical energy consumption in a machining process can be achieved by developing energy efficient machine tool components and/or by optimizing the actual machining process [7]. The design of energy efficient machine tools is also supported by international regulations (ECODESIGN Directive 2009/125/EC, Energy Labelling Regulation (Regulation (EU) 2017/1369), CECIMO Self-Regulatory Initiative) and standards (ISO 14955-1:2017, ISO/TR 14062:2002) [8]. Despite these regulations and standards, the development of new energy-efficient machine tool technology and the replacement of existing technology represent a gradual and cost intensive process. Therefore, the alternative approach of improving the energy consumption in the actual machining process is also of paramount importance. The efforts to improve energy consumption in machining processes greatly depend upon the methods used to define and collect primary energy consumption data from machine tools [9]. Different studies present in the literature have used different responses such as total/cutting power (P), total/cutting energy (E), power factor (PF), specific cutting energy (SCE), etc. Of the various responses used, SCE is considered as the most robust response to depict efficiency of a machining process because it incorporates both the cutting power and volume of material removed [10]. Furthermore, previous studies have also shown that SCE only takes into account energy consumed in the actual cutting process and disregards the effects of the make, type, size, and efficiency of machine tools [11]. An extensive amount of literature exists that analyzes the energy consumption in machining processes. [PERSON] and [PERSON] [12] have provided an excellent up-to-date review of such efforts, and interested readers are directed to consult their work. For the purposes of brevity, only key studies relevant to SCE have been discussed in this paper. The approaches used by past researchers to analyze SCE can be broadly classified into three categories, namely SCE modelling, optimization of machining process parameters, and SCE process maps. [PERSON] et al. [13] did pioneering work in the modelling of SCE and expressed it as the ratio of cutting power and the removed amount of material. Their results showed that specific energy reduces as the cutting speed, feed, and depth of the cut are increased.