Effect of electroosmosis on lubricant penetration at the tool–chip interface

Abstract

Conventional microcapillary lubrication theories explain lubricant penetration into capillaries at the tool–chip interface under the action of atmospheric pressure and capillary force without considering the electrokinetic effect caused by triboelectrification. In this study, the effect of electroosmosis on the penetration of water-based cutting fluid at the tool–chip interface of a turning process was investigated for the first time. An ionic adsorption model was proposed to adjust the zeta potential of different tool and workpiece materials in fluids, and a self-excited electric field at the tool–chip interface was obtained using an exoelectron emission test. The electroosmotic force related to the zeta potential and electric field intensity can regulate electrically driven fluid penetration. Cutting tests with a fixed self-excited electric field indicated that the cutting force obtained using a higher zeta potential fluid was lower than that obtained using deionized water and reversed zeta potential fluids (e.g. significant declines of 31.1 % and 44.3 % in AISI 304 turning). Moreover, scanning electron microscopy and energy dispersive X-ray spectroscopy analyses on the worn tool edges produced using the above fluids indicated a transfer from adhesive wear to micro breakage, which explains the positive correlation between penetration and zeta potential, owing to an elevated electroosmosis effect. The results presented in this paper are significant for understanding the influence of the electroosmosis effect on lubricant penetration to perfect the microcapillary lubrication theory and provide a reference for formulating metal working fluids.