A novel laser-induced fluorescence concept for thermometry measurements in machining lubricoolants

Abstract

This study investigates a two-colour laser-induced fluorescence (LIF) technique for thermometry in cooling lubricants (CL) for machining. The diagnostic technique should enable a simultaneous determination of cooling film thickness and film temperature, which is relevant for typical machining processes like turning and milling processes. The temperature determination is based on a temperature-sensitive fluorescence intensity ratio of a special dye determined in suitable spectral regions representing common band pass filters. For this purpose, two CL emulsions CL6 (6 vol.% CL, 94 vol.% water; normal machining) and CL10 (10 vol.% CL, 90 vol.% water; heavy machining) and its individual components were doped with the fluorescence dye Eosin-Y. Temperature dependent spectral LIF intensities were recorded in the range of 273–313 K, which are relevant for milling and cutting operations. Furthermore, absorption spectra were analysed as well. The temperature-dependent fluorescence measurements revealed a temperature limit for the emulsion stability. The emission peaks of Eosin-Y are shifted with increasing temperature towards longer wavelengths. The sensitivities of CL10 (1.88%/K) and CL6 (1.58%/K) are comparable to or even higher than the sensitivities of other LIF dyes provided in the literature. The literature-based dyes were however not determined in those CL. The measurements showed, that the investigated tracer-CL/water emulsions mixed with the dye enable a reliable temperature determination.