Investigating the industrial impact of hydraulic oil contamination on tool wear during machining and the development of a novel quantification methodology

Water based metalworking fluids (MWFs) commonly used for cooling and lubrication during machining are utilised in combination with cutting tools, work materials, fixtures and machine tools. However, they are an often overlooked component of the overall machining process, despite the fact that in some reported cases MWF costs were twice that of tooling costs. During its life cycle in a machine tool, the MWF is exposed to changes due to a range of factors which impact its quality and longevity. The key process variables (KPVs) reviewed in this study are MWF concentration, hydraulic (tramp) oil, solid particulates, water quality, MWF pH and microbial contamination. The aim of the present work is to highlight these KPVs which impact machining quality and health and safety, and to present industrially applicable measurement, monitoring and control (MMC) methods and techniques. This review is supported by a machining case study which demonstrates the impact of a single KPV—hydraulic (tramp) oil on MWF quality and machining output, and the need for applying MMC methods. Continuous hydraulic (tramp) oil contamination into the cutting fluid can cause tool life and wear to vary by 70%. A novel quantification methodology with gas chromatography was developed in this study to quantitatively measure hydraulic (tramp) oil contamination present within MWF and verified through experiments. The study overall highlights the need to apply a strict maintenance programme to increase the MWF lifetime and maintain performance for improved production, experimental process control and operator health and safety.