Providing environmentally friendly conditions and optimizing energy consumption are two essential requirements in order to achieve sustainable machining processes. One of the major sustainable machining concerns is the implementation of cutting fluids due to its significant impact on the machining quality characteristics. In addition, several economic, environmental, and health problems take place due to the inappropriate application of cutting fluids, therefore, previous research has introduced advanced cutting fluids technologies in order to optimize the cutting fluids usage during machining. However, there are still issues related to machining difficult-to-cut materials that have not been addressed and need to be improved. These materials have superior characteristics such as high strength to weight ratio, corrosion resistance, temperature resistance, and chemical stability, allowing them to be materials of choice in the aerospace, automotive, oil and gas, and bio-medical industries. Despite their desired characteristics, the wide spread applications of these materials has been compromised by several difficulties that arise during machining.

Flood cooling is a typical cooling strategy used in industry to dissipate the high heat generated during machining difficult-to-cut materials;​ however, the use of flood coolant has raised environmental and health concerns which call for different alternatives. Minimum Quantity Lubricant (MQL) has been successfully utilized as an acceptable coolant strategy;​ however, its potential to dissipate heat is much lower than the one achieved by flood coolant. One of the best techniques to enhance MQL heat capacity is the application of nano-cutting fluids as they offer significant enhancement in the tribological and heat transfer characteristics.

The main objective of the proposed research is to fully investigate and understand the influence and role of dispersed multi-walled carbon nano-tubes (MWCNTs) into vegetable oil by implementing the minimum quantity lubrication (MQL) technique during turning Ti-6Al-4V titanium alloy and Inconel 718. The Investigations include study of the energy consumption, tool wear behavior, chip morphology, and surface quality when using nanocutting fluids based MQL. The study revealed that nano-fluid based MQL improves the tool performance and proves clear advantage over the traditional/classical MQL.

In order to provide a solid physical understanding of the studied cutting processes using MQL-nano-fluids, the tribological aspects of the process and heat transfer mechanisms have been analyzed and investigated. The study presented a comparative performance analysis between MWCNTs and aluminum oxide (Al2O3) nano-cutting fluids. Additionally, an integrated finite element (FE) model has been developed in order to simulate the thermal and frictional effects of the MQL-nano-fluid to study various unique cutting aspects such as generated cutting temperature and residual stresses.

Furthermore, a general and detailed assessment model is developed and used to assess the sustainability of machining processes. Energy consumption, machining costs, waste management, environmental impact, and personal health and safety have been used to express the overall sustainability assessment index. It should be stated that the model predictions agree with the experimental findings. As such, the developed model offers a valuable tool to optimize the sustainability aspects of machining process.