24th International Colloquium Tribology - January 2024 139 Enhancing Machining Efficiency and Sustainability of Ti-6Al-4V through MQL with Polymeric Ester Based Metalworking Fluids: A Comparative Study with Conventional Cutting Fluids Ramazan Hakkı Namlu 1* , Kübra Kavut 2 , Hanife Gülen Tom 2 1 Atılım University, Manufacturing Engineering Department, Ankara, Turkey 2 Belgin Oil, R&D Department, Kocaeli, Turkey * Corresponding author: namluramazan@gmail.com 1. Introduction Ti-6Al-4V material is a widely used alloy across various fields, particularly in the aerospace and biomedical sectors, owing to its exceptional corrosion resistance, favorable strength-to-weight ratio, and biocompatibility properties. Machining operations serve as crucial production methods in transforming Ti-6Al-4V into the final product. However, various challenges such as high cutting forces, inadequate surface finish and shortened tool life arising from Ti-6Al-4V‘s very limited machinability due to its low thermal conductivity and high chemical reactivity make its machining challenging [1, 2]. For this reason, it is often referred to as a „difficult to cut“ material. To address these challenges, cutting fluids play a vital role by positively influencing operational efficiency, primarily aiming to reduce friction and dissipate heat. Nonetheless, Conventional Cutting Fluids (CCF) have several disadvantages, such as the requirement for excessive consumption, limited productivity increase, and adverse effects on the environment and operator health [3]. Thus, alternative methods emerged such as Minimum Quantity Lubrication (MQL). The MQL method aims to improve machining performance with advanced penetration into the cutting area through the aerosol delivery of a compressed air and oil mixture, while minimizing the impact on the environment and operator health with significantly reduced fluid consumption [4]. To optimize the benefits of MQL, careful selection of the appropriate fluid for the material used is crucial. This study investigates various polyol and polymeric ester based MQL fluids with distinct properties in the slot milling of Ti-6Al-4V, focusing on differences in cutting forces, surface roughness and surface topography compared to CCF. 2. Methodology The experimental setup can be seen in Figure 1. Four different slot milling operations were conducted with a constant cutting speed of 95 m/ min, a feed rate of 0.07 mm/ tooth, and a depth of cut of 1 mm. Each experiment was repeated three times in order to obtain repeatability. MQL fluids are formulated with three different esters: Trimethylolpropane Ester (TMPE) and Polymeric Ester (PE) with a viscosity index (VI) of 180 and PE with a VI of 221, which have a similar additive structure, contain water at a constant rate to increase the cooling effect in the tough machining of the Ti-6Al-4V alloy. All MQL fluids were applied to the cutting zone through two external nozzles with a flow rate of 50 ml/ h. In order to compare the MQL fluids, vegetable based CCF was utilized as a reference experiment for standard conventional operations with a flow rate of 50 l/ h and oil-water mixture ratio of 8%. The cutting forces are measured by Kistler 9265B dynamometer by using DynoWare software and the surface measurements were taken by Alicona InfiniteFocus optical surface roughness measurement device. Figure 1: The experimental setup 3. Results and discussion The cutting force results can be seen in Figure 2 while surface roughness and topography images are shown in Figures 3 and 4, respectively. The results indicate that all MQL experiments exhibited reduced cutting forces and surface roughness values compared to CCF. The surfaces obtained after MQL application displayed greater homogeneity, uniformity, and lower peak-to-valley values compared to CCF. The aerosolized delivery of MQL facilitated improved penetration between the cutting tool and the workpiece, effectively reducing wear and mitigating heat generation within the cutting zone. Ti-6Al-4V’s poor thermal conductivity challenges cutting due to heat concentration. MQL enhances cutting efficiency by minimizing this challenge [5]. 140 24th International Colloquium Tribology - January 2024 Enhancing Machining Efficiency and Sustainability of Ti-6Al-4V through MQL with Polymeric Ester Based Metalworking Fluids Figure 2: Cutting force results Figure 3: Surface roughness results When comparing different MQL fluids, it was determined that the PE formulation with higher viscosity index exhibited the lowest cutting force and achieved the best surface quality in terms of surface roughness and topography. Based on the results, it has been seen that the implementation of MQL, which demonstrates environmental friendliness and superior machining efficiency, outperforms CCF in the milling of Ti-6Al-4V material, yielding more effective machining outcomes. Furthermore, it has been ascertained that MQL fluids formulated with PE with outstanding thermal and oxidative stability, high viscosity index and excellent lubricity have been found to provide a maximum increase in efficiency. In light of these findings, it is evident that PE MQL fluids exhibiting offer a preferable alternative to CCF usage in terms of promoting sustainability and machining performance. Figure 4: Surface topography of cutting fluids 4. Conclusions In this study, the cutting forces and surface quality of Ti-6Al-4V material in slot milling operation were investigated using MQL with three different types of fluids. The obtained results can be summarized as follows: • MQL application, regardless of the type of oil used, resulted in lower cutting forces and surface roughness compared to CCF, while also providing a more homogeneous and uniform surface topography. • Among the different MQL oils tested, polymeric esters performed better than trimethylolpropane esters. • When examining polymeric esters among themselves, it was observed that polymeric esters with a high viscosity index yielded the best results. 5. Acknowledgement The MQL fluids used in this study were developed within the scope of the project labeled ARISEN, coded S0411, and financially supported by SMART Eureka. The authors express their gratitude to Atılım University Metal Forming Center of Excellence for their assistance in conducting the surface measurements. This research is partially funded by The Scientific and Technological Research Council of Turkey (TÜBİTAK), under grant number 222M381. References [1] E. O. 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