Integrated source reduction and treatment of metalworking fluid wastewater through induction-assisted dry hard turning of hardened SKD61 Steel

Metalworking-fluid wastewater from hard turning contains oil, suspended solids, metallic fines, and persistent organic pollutants, creating an environmental challenge for machining workshops. This study proposes an integrated water-management framework combining source reduction during machining, electrocoagulation treatment, and fit-for-purpose reuse. Hardened SKD61 steel was processed by induction-assisted dry hard turning using localized induction heating and HSS tooling. Raising the induction temperature from 350 to 600 °C reduced the average cutting force from 425.0 to 367.8 N and improved surface roughness from 1.40 to 1.02 µm, confirming stable dry or near-dry machining. Conventional wet turning, low-coolant turning, and induction-assisted dry turning were compared in terms of wastewater volume, pollutant load, treatment response, and suitability for reuse. Induction-assisted dry turning reduced wastewater generation from 2.40 to 0.18 L/workpiece and lowered COD load from 11.64 to 0.11 g/workpiece. Electrocoagulation of the residual stream achieved 86.8% COD removal, 93.5% oil and grease removal, 90.4% TSS removal, and 94.1% turbidity removal, reducing the residual COD load to 0.015 g/workpiece. The study identifies pilot validation, reliability, sludge management, and advanced polishing needs for higher-grade reuse. The proposed route offers a decentralized strategy for coolant minimization, wastewater treatment, and partial circular water use in machining workshops.