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This study investigates the critical maximum undeformed equivalent chip thickness for ductile-brittle transition ( DBh max -e ) of zirconia ceramics under different lubrication conditions. A DBh max -e model is developed through geometry and kinematics analyses of ductile-mode grinding. Result shows that DBh max -e decreases with increasing friction coefficient ( μ ). An experimental investigation is then conducted to validate the model and determine the effect of dry lubrication, minimum quantity lubrication (MQL), and nanoparticle jet minimum quantity lubrication (NJMQL) conditions on DBh max -e . According to different formation mechanisms of debris, the grinding behavior of zirconia ceramics is categorized into elastic sliding friction, plastic removal, powder removal, and brittle removal. Grinding forces per unit undeformed chip thickness ( F n/h and F t/h ) are obtained. The lubrication condition affects the normal force and ultimately influences the resultant force on workpiece. In comparison with dry grinding ( DBh max -e = 0.8 μm), MQL and NJMQL grinding processes increase DBh max -e by 0.99 and 1.79 μm respectively; this finding is similar to model result. The theoretical model is then assessed by different volume fractions of nanofluids under NJMQL condition with an average percentage error of less than 8.6%. [ABSTRACT FROM AUTHOR]

In accordance with the lubricating performance of nanofluid minimum quantity lubrication (N-MQL) grinding with different vegetable oils as the base oil in previous research, cooling performance was explored with a new method. Friction coefficient, specific friction energy, total heat flow density, and grinding peak temperature were used as evaluation parameters. The influence of the physical properties (viscosity, surface tension) of vegetable oils on the cooling effect was analyzed comprehensively. For the new method, a new ploughing force model and a friction force model were established, and cutting force and ploughing force were calculated theoretically. Afterward, friction force was obtained according to the theoretical model and experimental results and was used to calculate the evaluation parameters. The vegetable oil nanofluids showed better cooling performance than mineral oil because of their lubrication-favorable fatty acid molecules. Furthermore, the mechanism of the effect of nanofluid viscosity and surface tension on cooling performance was explored. Vegetable oil with a low viscosity and surface tension showed good cooling performance and that with a high viscosity and surface tension showed good lubrication performance. As a result, palm oil nanofluid with a high viscosity and surface tension achieved the lowest friction coefficient (0.258), specific friction energy (27.09 J/mm 3 ), and grinding peak temperature (123.8 °C) and exhibited better grinding performance than the others. [ABSTRACT FROM AUTHOR]

Given the increasing attention to environmental and health problems caused by machining, the development of an environment-friendly grinding fluid has become an urgent task. As an environment-friendly grinding fluid, vegetable oil has gained considerable attention. In this study, seven typical vegetable oils (i.e., soybean, peanut, maize, rapeseed, palm, castor, and sunflower oil) were used as the minimum quantity lubrication (MQL) base oil to conduct an experimental evaluation of the friction properties of the grinding wheel/workpiece interface. With nickel-based alloy GH4169 as workpiece material, the flood grinding working condition and MQL grinding working condition (i.e., using the seven vegetable oils and paraffin oil) were selected. The evaluation of the lubrication property mainly referred to grinding force, friction coefficient, specific grinding energy, and grinding ratio (G-ratio), as well as surface morphology and surface roughness. Experimental results indicated that MQL grinding using vegetable oil achieved a lower friction coefficient, specific grinding energy, and grinding wheel wear than flood grinding. Among the grinding fluids, castor oil achieved the best lubrication property and the best surface quality of workpiece. Castor oil had a friction coefficient and specific grinding energy of 0.30 and 73.47 J/mm 3 , which decreased by 50.1% and 49.4%, respectively, compared with flood grinding. Moreover, various grinding fluids changed cutting forces through changes in their lubrication property and further changed G-ratio. However, lubrication property was one of factors that influenced the G-ratio. Maize oil had the highest G-ratio of 29.15. Peanut, sunflower, and soybean oil with more saturated fatty acids, castor oil with more castor acids, and palm oil with numerous palmitic acids were suitable as lubricating fluids. [ABSTRACT FROM AUTHOR]