# Sustainability-Based Analysis of Conventional to High-Speed Machining of Al 6061-T6 Alloy
## 1 Introduction
[PERSON] and [PERSON] [5] proposed experimental models of specific energy at the process level on  
Figure 1: Energy consumed in a machining process. steel and aluminum alloys. They concluded that since the machine tool is a complex system, empirical models are expected to provide more accurate results. Mechanistic and empirical modellings were hybridized in the work of [PERSON] et al. [14] who developed an improved specific energy model for milling machines. [PERSON] et al. [10] employed specific energy to evaluate the efficiency of the machining process. Their results highlighted that lower undeformed chip thickness initiates plowing and results in higher specific energy consumption. [PERSON] et al. [15] investigated the effect of tool wear on specific energy at the machine level, spindle level, and cutting level in the hard milling process. The results showed that specific energy increased with the increase in tool wear. In order to achieve energy savings at the process level, the optimization of cutting parameters has often been used by past researchers. [PERSON] [16; 17] used Taguchi methods and response surface methodology (RSM) to analyze surface finish and power consumption along with SCE in the low-speed turning of Al 6061 T6 alloys. Their findings revealed cutting feed to be the most significant cutting parameter affecting surface finish and SCE. [PERSON] et al. [18] analyzed recoil force and SCE in the turning operation of AISI 1060 steel. Their results showed that the simultaneous minimization of SCE and recoil force results in the selection of conflicting machining parameters. [PERSON] et al. [19] employed a grey-relational analysis (GRA) technique along with an analytic hierarchy process (AHP) in the multi-objective optimization of Al 6061 alloys. Their results showed that the proposed machining strategy can result in the simultaneous improvement of SCE and the material removal rate (MRR). Inspired by this work, [PERSON] et al. [20] extended the proposed methodology in the turning of Ti-6 Al-4V. [PERSON] et al. [21] analyzed SCE consumption, tool wear, and surface roughness in the dry, wet, and cryogenic turning of Ti-6 Al-4V. Their results showed that surface roughness and tool wear substantially improved in wet and cryogenic cutting conditions as compared to dry cutting conditions. SCE consumption was observed to be less in the dry cutting condition as compared to the wet cutting condition because of the thermal softening gain at higher temperatures. However, cryogenic cooling reduces the work hardening of titanium alloys; therefore, SCE was reported to be the lowest in the cryogenic environment as compared to dry and wet cutting conditions. Similarly, [PERSON] et al. [22] and [PERSON] et al. [23] modelled and analyzed the specific cutting energy demand for the cryogenic and minimum quantity lubrication (MQL)-assisted machining of Ti-6 Al-4V alloys. Their results also demonstrated that cryogenic cutting conditions reduce SCE consumption. The importance of cutting fluids has been widely reported in the machining of difficult-to-cut alloys (such as Ti and Ni alloys) due to their positive effect on the machined surface quality, cooling, lubrication, chip removal, and tool life [24]. In spite of these benefits, the environmental hazards associated with the coolants make them undesirable for sustainable machining practices [25]. Furthermore, in the case of relatively soft materials such as aluminum alloys that have a high machinability rating, a cutting distance in the order of kilometers has been reported before measurable tool wear could be observed [26; 27]. Therefore, several past studies have employed dry cutting conditions for the evaluation of SCE in the machining of aluminum alloys [19; 28; 29]. The authors pioneered the concept of presenting SCE consumption as process maps [11; 30; 31]. The developed energy maps categorized SCE consumption in five distinct regions with respect to various machining parameters.