Comparing energy and water use of aqueous and gas‐based metalworking fluids

Gas‐based metalworking fluids (MWFs) have been proposed as alternative coolants and lubricants in machining operations to mitigate concerns surrounding water use and pollution, industrial hygiene, occupational health, and performance limitations associated with water‐based (aqueous) MWFs that are ubiquitously used in the metals manufacturing industry. This study compares the primary energy and water use associated with the consumptive use, delivery, and disposal of aqueous MWFs with three gas‐based MWFs in the literature—minimum quantity lubricant‐in‐compressed air (MQL), liquid/gaseous N2, and liquid/supercritical CO2. The comparison accounts for reported differences in machining performance in peer‐reviewed experimental studies across several machining processes and materials. The analysis shows that despite the reported improvement in tool life with N2 and CO2‐based MWFs, the electricity‐ and water‐intensive separation and purification processes for N2 and CO2 lead to their higher primary energy and water use per volume of material machined relative to water‐based MWFs. Although MQL is found to have lower primary energy use, significant consumptive water use associated with the vegetable oil commonly used with this MWF leads to higher overall water use than aqueous MWF, which is operated in a recirculative system. Gas‐based MWFs thus shift the water use upstream of the manufacturing plant. Primary energy and water use of gas‐based MWFs could be reduced by focusing on achieving higher material removal rates and throughput compared to aqueous MWF instead of solely targeting improvements in tool life. Additionally, the consumptive use of CO2 and N2 MWFs could be minimized by optimizing their flow rates and delivery to precisely meet the cooling and lubrication needs of specific machining processes instead of flooding the tool and workpiece with these gases. This article met the requirements for a gold–gold JIE data openness badge described at http://jie.click/badges.