Effect of minimum quantity lubrication on surface integrity in high-speed grinding of sintered alumina using single layer diamond grinding wheel

Abstract

Exceptional properties of advanced ceramics attract various heavy engineering industries. But surface and sub-surface defects generated during final stage abrasive machining processes make them vulnerable and limit their widespread use. This study aims to provide an understanding of the effectiveness of Minimum Quantity Lubrication (MQL) in reducing surface and sub-surface damages in high-speed grinding of brittle materials. In the present work, high-speed grinding of alumina was performed under MQL-neat oil, MQL-soluble oil (5% concentration in water) and conventional wet grinding environment with the single layer electroplated diamond grinding wheel. In-depth analysis of surface topology, surface morphology, residual stress and sub-surface damage was carried out using 3D surface profilometer, scanning electron microscope, X-ray diffractometer, and X-ray micro-CT, respectively. Grinding under MQL-neat oil provided leptokurtic (peaky) surface profile due to increased plastic deformation, whereas conventional wet grinding generated platykurtic (plateaued) surface profile because of brittle fracture. A simple model has been proposed to understand the underlying mechanism of generation of peaky and plateaued type of surface in grinding due to ductile deformation and brittle fracture, respectively. Morphological observation of the sample ground under MQL-neat oil showed distinct microcutting and ploughing marks. MQL-neat oil condition also provided more compressive residual stress and less sub-surface damage than other grinding environments. This is attributed to increased plastic deformation due to efficient lubrication under the MQL-neat oil grinding regime. The mechanism of increased plastic deformation and reduced sub-surface damage due to improved lubrication under MQL in high-speed grinding of brittle materials has been discussed.