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Titanium alloy Ti6Al4V is of great importance to the aeronautical and medical sectors due to its mechanical properties such as a high strength-to-weight ratio and corrosion resistance. On the downside, machining Ti6Al4V can lead to accelerated tool wear and poor surface finish of the machined part due to its low heat dissipation capacity. Traditionally, oil and water based metalworking fluids (MWFs) have been used to overcome such issues. However, new regulations and eco-friendly manufacturing trends suggest that conventional MWFs should be minimised, as they are hazardous to the environment and workers' health. Additionally, titanium prostheses contaminated with oil can cause severe integration problems on the patient. This article researches the feasibility of replacing conventional emulsions with sustainable liquid carbon dioxide (LCO 2) cooling. For this purpose, an optimisation of the tool geometry (helix angle, clearance angle and cutting edge geometry) for LCO 2 assisted milling of Ti6Al4V was carried out, taking into account parameters such as cutting forces, surface roughness and the microstructure of the machined surface. This research contributes to the development of environmentally friendly and work safe manufacturing processes that meet the challenges of machining Ti6Al4V for aerospace and medical applications. [ABSTRACT FROM AUTHOR]

Carbon fibre reinforced polymer/titanium stacks (CFRP/Ti6Al4V) are employed in aeronautics due to their excellent weight-to-strength ratio and corrosion properties. However, these same material properties present challenges for hole making which cannot be solved using conventional water-based metalworking fluids (MWFs), as they cause degradation of the composite. Moreover, environmental and health concerns require exploration of alternative cooling/lubrication solutions. In this study, a controlled mixture of liquid carbon dioxide (LCO 2) and minimum quantity lubrication (MQL) was supplied through the drilling tool. The effect of varying LCO 2 and MQL flow rates was evaluated on cutting forces, temperatures, and several hole quality outputs. The optimal flow rates were then determined through multi-objective optimisation. The results show that the cooling/lubrication flow rate greatly affects the measured outputs, and that supplying LCO 2 + MQL with optimised flow rates helps achieve superior quality holes in CFRP, Ti6Al4V and CFRP/Ti6Al4V stacks. [ABSTRACT FROM AUTHOR]