Performance Evaluation of Solid Lubricants Under Machining-Like Conditions

Abstract

Modern trends in machining include sustainable manufacturing with the focus on reducing the consumption of conventional cutting fluids. These alternative cooling-lubrication principles include Minimum Quantity Lubrication (MQL), cryogenic machining and dry machining. In the absence of abundant quantities of cutting fluid, adequate lubrication is needed, especially when difficult-to-machine materials are considered. High friction during machining leads to heat generation, which adversely affects the tool life, workpiece surface quality and energy consumption. Consequently, lower cutting speeds are employed. Solid lubricants such as molybdenum disulphide or graphite provide excellent lubrication in severe conditions, where contact pressures and temperatures exceed the operational limits for conventional oils. These solid lubricants can be added to cutting fluids, e.g. in oil for MQL, to enhance their thermal and tribological properties. Their unique structure can provide lower friction coefficient, thus reducing the generated heat and prolonging the tool life. Presented in the paper is a performance evaluation of solid lubricant (MoS2, average particle size 2 μm) from the tribological viewpoint. An open tribometer has been developed to estimate the friction coefficient between uncoated carbide tool and AISI 1045 workpiece at machining-like conditions which include high contact pressures and sliding speeds. To show the potential of solid lubricant, a comparison has been made with dry, flooding, MQL, cryogenic and combination of MQL and cryogenic conditions. Molybdenum disulphide showed excellent lubrication performance under all considered sliding speeds, outperforming the conventional lubricants, opening the possibility of further research in the area of solid lubricant assisted machining.