Formulation of Sustainable Water-Based Cutting Fluids with Polyol Esters for Machining Titanium Alloys

Elisabet Benedicto,Laurent Aubouy,María Ana Sáenz-Nuño,Eva María Rubio

doi:10.3390/met11050773

Abstract

The machinability of titanium alloys still represents a demanding challenge and the development of new clean technologies to lubricate and cool is greatly needed. As a sustainable alternative to mineral oil, esters have shown excellent performance during machining. Herein, the aim of this work is to investigate the influence of esters’ molecular structure in oil-in-water emulsions and their interaction with the surface to form a lubricating film, thus improving the efficiency of the cutting fluid. The lubricity performance and tool wear protection are studied through film formation analysis and the tapping process on Ti6Al4V. The results show that the lubricity performance is improved by increasing the formation of the organic film on the metal surface, which depends on the ester’s molecular structure and its ability to adsorb on the surface against other surface-active compounds. Among the cutting fluids, noteworthy results are obtained using trimethylolpropane trioleate, which increases the lubricating film formation (containing 62% ester), thus improving the lubricity by up to 12% and reducing the torque increase due to tool wear by 26.8%. This work could be very useful for fields where often use difficult-to-machine materials—such as Ti6Al4V or γ-TiAl—which require large amounts of cutting fluids, since the formulation developed will allow the processes to be more efficient and sustainable.

Highlights

Published: 8 May 2021Titanium alloys, Ti6Al4V, are used extensively in the aeronautic, aerospace, automotive, chemical, and biomedical industries due to their unique mechanical properties (Table 1), such as high specific strength, hardness, corrosion resistance at high temperatures, and biocompatibility [1]
The formation of the lubrication layer was calculated according to the equations of the regression line abstracted from the calibration curve of each polyol ester cutting fluid under study (Table 5)
This study provides an evaluation of the influence of polyol esters in oil-in-water (O/W) emulsions on titanium alloys to overcome the challenges in formulating sustainable water-based cutting fluids

Summary

Introduction

Ti6Al4V, are used extensively in the aeronautic, aerospace, automotive, chemical, and biomedical industries due to their unique mechanical properties (Table 1), such as high specific strength, hardness, corrosion resistance at high temperatures, and biocompatibility [1]. Despite these exceptional properties, Ti6Al4V is classified as a difficult-to-cut material because of its high chemical affinity, low thermal conductivity, and work hardening. Due to the low conductivity of Ti6Al4V, the heat generated during machining cannot be dissipated throughout the workpiece and chips effectively. The creation of the lubricating film depends on the media composition, the absorption and chemisorption of polar or metal-active additives on the surface of the workpiece, while the coolant and cleaning capacity depends on the physical

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